Dissertations / Theses on the topic 'Refractive surgery'

Thesis (M.A.)--Boston University
Procedures to reshape the cornea to correct refractive errors have been a longstanding and fast-evolving area of interest for centuries. As recent advances in excimer laser technology allow keratorefractive treatments to deliver precise treatments with fewer associated risks and complications, the popularity of modern refractive procedures continues to grow at unprecedented rates. For this reason, it is imperative to continue correlating patient characteristics to outcomes so that refractive surgeons can more accurately foresee the results of the selected procedure. This study examined the outcomes of refractive surgeries at a full-scope ophthalmology clinic from January 2011 to November 2011. The main objectives of th is study were to determine the differences between the outcomes of LASIK vs. LASEK, Custom vs. Traditional treatment plans, myopic vs. hyperopic patients and MMC exposure vs. no MMC exposure (LASEK only). More importantly, the data was scrutinized to determine whether or not any of these treatments and/or patient characteristics correlated with poor visual outcomes or the need for an enhancement. Of the 590 myopic eyes treated with Custom LASIK, 90.85% (n=536 eyes) had UDVA of 20/20 or better, 96.10% (n=567 eyes) had UDVA of 20/25 or better and 99.32% (n=586 eyes) had UDVA of 20/40 or better. Of the 170 myopic eyes treated with Custom LASEK, 70.59% (n=120 eyes) had a UDVA of 20/20 or better, 82.94% (n=141 eyes) had a UDVA of 20/25 or better and 96.47% (n=164 eyes) had a UDVA of 20/40 or better. Of the 45 hyperopic eyes that were treated with Traditional LASIK, 44.44% (n=20 eyes) had postoperative UDVA of 20/20 or better, 62.22% (n=28 eyes) had postoperative UDVA of 20/25 or better and 82.22% (n=37 eyes) had postoperative UDVA of 20/40 or better. Of the 536 eyes receiving LASIK, 91.42% (n=490 eyes) had an UDVA of 20/20 or better, 96.46% (n=517 eyes) had an UDVA of 20/25 or better and 99.44% (n=533 eyes) had an UDVA of 20/40 or better. Of the 146 low or moderately myopic eyes receiving Custom LASEK, 74.65% (n=106 eyes) had an UDVA of 20/20 or better, 86.62% (n=123 eyes) had an UDVA of 20/25 or better and 96.48% (n=137 eyes) had an UDVA of 20/40 or better. Of the 54 highly myopic eyes treated with Custom LASIK, 85.19% (n=46 eyes) had an UDVA of 20/20 or better, 92.59% (n=50 eyes) had an UDVA of 20/25 or better, and 98.15% (n=53 eyes) had an UDVA of 20/40 or better. Of the 28 highly myopic eyes treated with Custom LASEK, 53.57% (n=15 eyes) had an UDVA of 20/20 or better, 64.29% (n=18 eyes) had an UDVA of 20/25 or better, and 96.43% (n=27 eyes) had an UDVA of 20/40 or better. An analysis of these data yields significantly greater percentages of myopic (low, moderate and high) eyes achieving 20/20 or better after treatment by Custom LASIK versus Custom LASEK. The data suggested no correlations between poor visual outcomes and/or the need for an enhancement treatment and intraoperative complications, magnitude of ametropia, pupil size, age, treatment type, and treatment plan. All of the LASEK patients who underwent an enhancement treatment were exposed to MMC during their original procedure. Hyperopic patients displayed significantly reduced visual outcomes than comparable myopic treatments. Future studies should investigate similar preoperative characteristics and attempt to correlate them to results to improve predictability and, thus, visual outcomes.

Introduction: This PhO study investigates finite objective and subjective clinical outcomes of refractive surgery. Methods: A series of studies was conducted to investigate laser retreatment procedures, a comparison between the OPO-Scan and WaveScan aberrometers, a comparison of aberrometry changes following laser in situ keratomileusis (LASIK) and laser-assisted subepithelial keratectomy (LASEK), internal aberration changes following LASIK, the development of a quality of vision (OoV) questionnaire and the refractive outcomes of the SCHWINO Amaris excimer laser. Results: Good visual and refractive outcomes were found with LASEK retreatment and a high incidence (23%) of epithelial ingrowth occurred following flap-lift LASIK retreatments. In the comparison between the OPO-Scan and WaveScan, medium consistency was found for aberrations z;' and z~ with poor consistency for all other aberrations. In the comparison between LASIK and LASEK, both procedures caused increases to spherical aberration with LASIK additionally causing increases to two fourth-order aberrations and LASEK causing increases to two fifth-order aberrations. Investigations into internal aberrations found LASIK increased internal spherical aberration which attenuated the increase in anterior corneal spherical aberration. A OoV questionnaire was successfully developed utilising Rasch analysis demonstrating good precision, reliability, and internal consistency with good construct validity and test-retest reliability. The SCHWINO Amaris was found to be effective for the treatment of a range of refractive errors. Conclusion: Significant clinical finding were found for laser retreatments and primary treatments with two different laser systems. Aberrations were found to be poorly correlated with the OPO-Scan and the WaveScan. An effective OoV questionnaire was developed which may be used in prospective clinical and research studies. •.

The principal work in this thesis describes the investigation of the impact that alterations to ocular aberrations following refractive surgery have on the accommodative mechanism. A series of prospective studies were conducted with healthy adults (n=36) that had chosen to undergo refractive surgery at Manchester Royal Eye Hospital. A variety of monocular accommodative functions were assessed prior to surgery and then at one and three months following surgery on the same cohort of patients. Accommodative functions included amplitude of accommodation, accommodative facility (at 6m and 0.4m) including positive and negative response times, and accommodative stimulus-response functions. Dynamic accommodation responses were examined in a subgroup (n=10) at three months following refractive surgery and compared to an age-matched emmetropic control group (n=10) to evaluate differences in latency, amplitude, time constant and peak velocity of accommodation and disaccommodation. During the studies, ocular aberrations were concurrently measured to determine whether alterations to aberrations could help explain any observed changes in accommodative functions. Evaluation of visual, refractive and questionnaire outcome measures indicated that the patient cohort underwent successful surgery. Following surgery, significant alterations to a number of accommodative functions were discovered. Mean subjective ocular amplitude of accommodation increased by approximately 0.50D (p<0.05), mean stimulus-response function gradient decreased by approximately 10% (p<0.05) and distance facility rate increased by approximately 2-3 cycles/minute (p<0.05). Significant correlation was found between the change in accommodative stimulus-response function gradient, and the change in spherical aberration following surgery (p<0.05). Significant differences were also found in the parameters of accommodative dynamics, although some of these factors may be explained by refractive error differences between the refractive surgery patients (pre-operative myopes) and the emmetropic control group. The results suggest that alterations to aberrations following refractive surgery may be capable of influencing elements of the accommodation response. Additional studies were conducted to investigate the changes in aberrations during accommodation (n=31 subjects), and explore the contribution of the tear film (n=19 subjects) to higher order aberrations in eyes that have undergone refractive surgery. The results suggested that the rate of change in aberrations during accommodation is not affected by refractive surgery, but that the pattern of aberrations induced by post-blink tear film changes may differ in patients that have undergone refractive surgery. A further study is presented which investigated the form of the accommodative stimulus-response function to grating target of different spatial frequencies in groups of myopic (n=10) and emmetropic (n=10) participants recruited from among the staff and students at The University of Manchester. Both refractive groups appeared to show similar accommodative behavior, however the dominant feature of the data in both groups was between subject variation.

Femtosecond lasers were introduced in ophthalmology initially for flap creation for LASIK. This thesis describes a body of work undertaken by the author exploring the possibility of using these lasers in corneal and refractive surgery. The use of the femtosecond laser in corneal and refractive surgery offered the prospect of better precision with respect to their accuracy in depth cut, and the smoothest of lamellar interface. The development of multiple laser platforms allowed us to perform comparative studies in both ex vivo/animal and clinical studies and to explore the prospect of a new refractive procedure, lenticule extraction and also lenticule re-implantation. The laser proved to be accurate in its vertical depth cutting and following optimization was able to cut a smoothe lamellar interface. The clinical study showed the laser to be safe and effective. The comparative studies showed the superiority of the lower energy femtosecond laser on IOP rise, without compromising on clinical outcomes, which were the same for both lasers. Femtosecond laser lenticule creation was optimised in animal models and then shown to be safe and efficacious in a clinical study. The wound healing benefits of an 'all in one' femtosecond laser procedure were evident, in both animal as well clinical studies. Lenticule reimplantation was shown to be effective in both the rabbit and monkey models. The use of the femtosecond laser is set to increase in ophthalmology. The work in this thesis has provided fundmental ex vivo, animal and clinical benefits on the the use of femtosecond lasers in corneal and refractive surgery. It has also envisioned a concept of lenticule re-implantation for future clinical use.

Thesis (Ph. D.)--Ohio State University, 2004.
Document formatted into pages; contains 137 p. Includes bibliographical references. Abstract available online via OhioLINK's ETD Center; full text release delayed at author's request until 2005 June 1.

Purpose: To improve the predictability, accuracy and stability of laser in-situ keratomileusis (LASIK), by evaluating the clinical, procedural and tissue response factors that affect refractive outcomes. Methods: Myopic LASIK surgeries (n=5,978) were carried out using the Technolas planoscan and Nidek EC-5000 excimer lasers. Clinical variables associated with a refractive outcome of within ??0.50 D of the target were identified using regression analysis. Possible procedural variations such as the timing of the procedure and accuracy of both the chosen keratome and excimer laser were evaluated. The predictability and accuracy of the ablation was assessed by measuring changes in corneal thickness during and after the procedure. Factors influencing the stability of refractive outcome were assessed. Results: Clinical factors associated with a refractive outcome of within ??0.50 D of the target included; corrections less than 5.00 DS (OR 0.21x, 95% CI 0.11-0.40x compared with corrections over -5.00 DS[referent]), patients younger than 40 years (patients over 50 OR 8.27x, 95% CI 3.41-20.03x, patients 40 to 50 years OR 1.93x, 95% CI 0.96-3.90x, compared with patients under 40[referent]) and average pre-operative curvatures between 43.50 and 45.50D (OR 0.39x, 95% CI 0.18-0.83 compared with curvatures of less than 43.50D [referent]). Refractive stability was improved using optic zone sizes between 5.5-6.0 mm, reduced myopic corrections, flatter pre-operative corneal curvatures and thicker corneal flaps (R??=25%, p<0.001). Procedural factors associated with poorer outcomes included: thinner measured flap thickness, deeper ablations and the use of the automated corneal shaper (ACS) microkeratome with a novice surgical team (R??=34%, p < 0.001). Delaying the ablation from 20 to 90 seconds (s) after flap lift was associated with a more stable refractive outcome at three months (p=0.017). In the 90 s following flap lift, the cornea thinned by 5??3%. The ablation rate per scan varied between procedures, however, the effect on refractive outcome was small (r=0.15, p=0.267). Changes in central corneal thickness indicated refractive stability (p=0.039). Conclusions: Applying the optimal clinical and procedural factors as described afforded a refractive outcome in a further 8% of cases, resulting in 94% to 96% of cases within ??0.50 DS of target. Refractive predictability was limited due to the inability of the keratome to produce a consistent corneal flap thickness and unexpected changes in corneal thickness. The accuracy of refractive outcome will decrease with larger ablations. The degree of refractive inaccuracy with high refractive corrections (> -10.00 D) can be over 1.00 D.

In this thesis the laser ray tracing (LRT) technique for measurement of ocular aberrations has been implemented, validated and applied, in conjunction with complementary techniques, to the study of ocular aberrations in human eyes. In particular, we studied optical aberrations in myopic and hyperopic eyes and the optical changes induced by refractive surgery for myopia and hyperopia. We have studied the impact of the optimisation of some experimental parameters on the estimation of the wave aberration. We demonstrated that although the polarisation state and wavelength of the illumination light affected the intensity patterns of the images obtained using reflectometric aberrometry (LRT and Hartmann Shack sensor), these changes did not affect the estimation of aberrations. We also showed that the difference in the defocus term (focus shift) due to the use of different wavelengths is in agreement with the Longitudinal Chromatic Aberration of the Indiana Chromatic Eye Model for average normal eyes, although intersubject variability is not negligible. In addition, we studied experimentally the influence of the geometrical distribution and density of the pupil sampling on the estimation of aberrations using artificial and normal human eyes, and performed numerical simulations to extend our results to "abnormal"eyes. We found that the spatial distribution of the samples can be more important than the number of samples, for both our measured as well as our simulated "abnormal" eyes. Experimentally, we did not find large differences across patterns except, as expected, for undersampled patterns. We found that hyperopic eyes tended to have more positive asphericity and greater total and corneal spherical aberrati on than myopic eyes, as well as greater 3rd and higher order aberrations. Although we found no significant differences between groups in terms of internal aberrations, internal spherical aberration showed a significant age-related shift toward less negative values in the hyperopic group. We also assessed the impact of the LASIK corneal surgery, a popular surgical technique for correction of refractive errors, on the optical quality for both myopic and hyperopic standard techniques. Third and higher order ocular and an terior corneal aberrations increased with the surgery. Ocular and corneal spherical aberration changed towards more positive values with myopic LASIK, and towards more negative values with hyperopic LASIK. Changes in internal spherical aberration were of opposite sign than those induced in corneal spherical aberration. Changes induced by hyperopic LASIK were larger than those induced by myopic LASIK for a similar attempted correction.

This thesis proposes and tests an individually customizable model of the human crystalline lens. This model will be crucial in developing both research on the human eye and driving diagnostic tools to help plan and treat optical issues, such as those requiring refractive surgery. This thesis attempts to meet two goals: first, it will determine whether this new lens model can reproduce the major aberrations of real human eyes using a computational framework. Second, it will use clinical information to measure how well this model is able to predict post-operation results in refractive surgery, attempting to meet clinical standards of error. The model of the crystalline lens proposed within this thesis is shown to be valid, as it is able to both reproduce individual patient's optical information, and correctly predicts the optical results of a refractive surgery of an individual human eye within clinical standards of error.

The purpose of this thesis is to describe the development of an anatomically based, young adult eye model, which includes a crystalline lens with a gradient refractive index (GRIN). This model will then be used to investigate the effect of laser refractive surgery. The first step in this process involved developing a symmetrical eye model that was found to be a better predictor of empirical longitudinal spherical aberration than any previous model. Myopia was simulated by either a purely axial or refractive technique. While these models were found to be good predictors of the spherical aberration measured in young adults, they did not predict the total amount of high-order aberrations. The techniques used to simulate a single type of myopia caused the myopic models to become anatomically inaccurate. To improve the eye models a biconic surface was used to quantify the anterior corneal shape as a function of myopia. A method to describe the refractive error and biconic shape parameters in Jackson Cross Cylinder terms was implemented to determine correlations. Results indicate that a biconic accurately models the average shape of the anterior corneal surface as a function of myopia. Adopting the biconic model for the anterior corneal surface and adding average misalignments of the ocular components transformed the models from symmetrical to asymmetrical. Refractive error was now simulated by the anatomically accurate changes in both the anterior corneal shape and axial length. The asymmetrical aberrations resulted from the misalignment of the ocular components and provided a good prediction of average empirical aberrations but underestimated the aberrations of individual subjects. Photorefractive keratectomy, a form of laser refractive surgery, was simulated by theoretically calculated and by empirically measured changes in the shape of the anterior corneal surface. Applying the change in anterior corneal shape to the asymmetrical models was used to develop postoperative models. Changes in corneal shape and model aberrations attributed to theoretical calculations do not match empirical observations. The prediction of increased high-order aberrations in postoperative models based on empirically measured changes in the anterior corneal topography was similar to clinical results. Average anatomically based, GRIN eye models have been developed that accurately predict the average aberrations of emmetropic and myopic young adults. These models underestimate the asymmetrical and total high-order aberrations that have been measured in individual subjects but are still useful for investigating the average effects of procedures like refractive surgery.

Overview: Optical concepts as they relate to the ophthalmologic correction of vision in corneal laser vision correction and intraocular lens design was examined. Purpose: The interaction between the excimer laser and residual corneal tissue in laser vision correction produces unwanted side effects. Understanding the origin of these artifacts can lead to better procedures. Furthermore, accommodating intraocular lenses offer a potential for eliminating presbyopia. Understanding the properties of a new accommodating intraocular lens incorporating a deformable interface may lead to advances in cataract surgery. Introduction: Corneal surface irregularities following laser refractive procedures are commonly seen. They regularly result in a patient’s decreased best corrected visual acuity and decreased contrast sensitivity. These changes are only seen in biologic tissue and the etiology has been elusive. A thermal response has been theorized and was investigated in this research. In addition, intraocular lenses using a mechanically deforming interface to change their power in order to duplicate natural accommodation have been developed. The deforming interface(s) induce optical aberrations due to irregular deformations. Design efforts have centered on minimizing these deformations. Both of the ophthalmic applications have been analyzed using finite element analysis (FEA) to understand their inherent optical properties. Methods: FEA modeling of thermal theory has been applied to verify that excimer laser induced collagen contraction creates corneal surface irregularities and central islands. A mathematical model which indicates the viability of the theory was developed. The modeling results were compared to post ablation changes in eyes utilizing an excimer (ArF 193 nm), as well as non-ablative thermal heating in eyes with a CO₂ laser. Addition modeling was performed on an Intraocular lens prototype measuring of actuation force, lens power, interface contour, optical transfer function, and visual Strehl ratio. Prototype verified mathematical models were utilized to optimize optical and mechanical design parameters to maximize the image quality and minimize the required force. Results: The predictive model shows significant irregular central buckling formation and irregular folding. The amount of collagen contraction necessary to cause significant surface changes is very small (0.3%). Uniform scanning excimer laser ablation to corneal stroma produces a significant central steepening and peripheral flattening in the central 3mm diameter. Isolated thermal load from uniform CO₂ laser irradiation without ablation also produces central corneal steepening and paracentral flattening in the central 3mm diameter. The iterative mathematical modeling based upon the intraocular lens prototype yielded maximized optical and mechanical performance through varied input mechanical and optical parameters to produce a maximized visual Strehl ratio and a minimized force requirement. Conclusions: The thermal load created by laser irradiation creates a characteristic spectrum of morphologic changes on the porcine corneal stromal surface which correlates to the temperature rise and is not seen inorganic, isotropic material. The highly similar surface changes seen with both lasers are likely indicative of temperature induced transverse collagen fibril contraction and stress re-distribution. Refractive procedures which produce significant thermal load should be cognizant of these morphological changes. The optimized intraocular lens operates within the physiologic constraints of the human eye including the force available for full accommodative amplitude using the eye’s natural focusing feedback, while maintaining image quality in the space available. Optimized optical and mechanical performance parameters were delineated as those which minimize both asphericity and actuation pressure. The methodology combines a multidisciplinary basic science approach from biomechanics, optical science, and ophthalmology to optimize an intraocular lens design suitable for preliminary trials.

Purpose: To determine whether symptoms of dizziness and fall rates change due to routine cataract surgery and to determine the influence of visual and refractive factors on these common problems in older adults. Methods: Self-reported dizziness and falls were determined in 287 subjects (mean age of 76.5±6.3 years, 55% females) before and after routine cataract surgery for the first (81, 28%), second (109, 38%) and both eyes (97, 34%). Six-month falls rates were determined using self-reported retrospective data. Dizziness was determined using the short-form of the Dizziness Handicap Inventory. Results: The number of patients with dizziness reduced significantly after cataract surgery (52% vs. 38%; χ2 = 19.14 , p < 0.001), but the reduction in number of patients who fell in the 6-months post surgery was not significant (23% vs. 20%; χ2= 0.87, p=0.35). Multivariate logistic regression analyses found significant links between post-operative falls and change in spectacle type (increased risk if switched into multifocal spectacles). Post-operative dizziness was associated with changes in best eye visual acuity and changes in oblique astigmatic correction. Conclusions: Dizziness is significantly reduced by cataract surgery and this is linked with improvements in best eye visual acuity, although changes in oblique astigmatic correction increased dizziness. The lack of improvement in falls rate may be associated with switching into multifocal spectacle wear after surgery.

Aberrations affect image quality of the eye away from the line of sight as well as along it. High amounts of lower order aberrations are found in the peripheral visual field and higher order aberrations change away from the centre of the visual field. Peripheral resolution is poorer than that in central vision, but peripheral vision is important for movement and detection tasks (for example driving) which are adversely affected by poor peripheral image quality. Any physiological process or intervention that affects axial image quality will affect peripheral image quality as well. The aim of this study was to investigate the effects of accommodation, myopia, age, and refractive interventions of orthokeratology, laser in situ keratomileusis and intraocular lens implantation on the peripheral aberrations of the eye. This is the first systematic investigation of peripheral aberrations in a variety of subject groups. Peripheral aberrations can be measured either by rotating a measuring instrument relative to the eye or rotating the eye relative to the instrument. I used the latter as it is much easier to do. To rule out effects of eye rotation on peripheral aberrations, I investigated the effects of eye rotation on axial and peripheral cycloplegic refraction using an open field autorefractor. For axial refraction, the subjects fixated at a target straight ahead, while their heads were rotated by ±30º with a compensatory eye rotation to view the target. For peripheral refraction, the subjects rotated their eyes to fixate on targets out to ±34° along the horizontal visual field, followed by measurements in which they rotated their heads such that the eyes stayed in the primary position relative to the head while fixating at the peripheral targets. Oblique viewing did not affect axial or peripheral refraction. Therefore it is not critical, within the range of viewing angles studied, if axial and peripheral refractions are measured with rotation of the eye relative to the instrument or rotation of the instrument relative to the eye. Peripheral aberrations were measured using a commercial Hartmann-Shack aberrometer. A number of hardware and software changes were made. The 1.4 mm range limiting aperture was replaced by a larger aperture (2.5 mm) to ensure all the light from peripheral parts of the pupil reached the instrument detector even when aberrations were high such as those occur in peripheral vision. The power of the super luminescent diode source was increased to improve detection of spots passing through the peripheral pupil. A beam splitter was placed between the subjects and the aberrometer, through which they viewed an array of targets on a wall or projected on a screen in a 6 row x 7 column matrix of points covering a visual field of 42 x 32. In peripheral vision, the pupil of the eye appears elliptical rather than circular; data were analysed off-line using custom software to determine peripheral aberrations. All analyses in the study were conducted for 5.0 mm pupils. Influence of accommodation on peripheral aberrations was investigated in young emmetropic subjects by presenting fixation targets at 25 cm and 3 m (4.0 D and 0.3 D accommodative demands, respectively). Increase in accommodation did not affect the patterns of any aberrations across the field, but there was overall negative shift in spherical aberration across the visual field of 0.10 ± 0.01m. Subsequent studies were conducted with the targets at a 1.2 m distance. Young emmetropes, young myopes and older emmetropes exhibited similar patterns of astigmatism and coma across the visual field. However, the rate of change of coma across the field was higher in young myopes than young emmetropes and was highest in older emmetropes amongst the three groups. Spherical aberration showed an overall decrease in myopes and increase in older emmetropes across the field, as compared to young emmetropes. Orthokeratology, spherical IOL implantation and LASIK altered peripheral higher order aberrations considerably, especially spherical aberration. Spherical IOL implantation resulted in an overall increase in spherical aberration across the field. Orthokeratology and LASIK reversed the direction of change in coma across the field. Orthokeratology corrected peripheral relative hypermetropia through correcting myopia in the central visual field. Theoretical ray tracing demonstrated that changes in aberrations due to orthokeratology and LASIK can be explained by the induced changes in radius of curvature and asphericity of the cornea. This investigation has shown that peripheral aberrations can be measured with reasonable accuracy with eye rotation relative to the instrument. Peripheral aberrations are affected by accommodation, myopia, age, orthokeratology, spherical intraocular lens implantation and laser in situ keratomileusis. These factors affect the magnitudes and patterns of most aberrations considerably (especially coma and spherical aberration) across the studied visual field. The changes in aberrations across the field may influence peripheral detection and motion perception. However, further research is required to investigate how the changes in aberrations influence peripheral detection and motion perception and consequently peripheral vision task performance.

This diploma thesis focuses on the definition of cyborgization and to delimit it. The cyborgizatoon of body is one of the ways of human improvement next to gene manipulation and neuromanipulation. It is difficult to express the specific definition because the experts have a different point of view, what for thesis shows various point of view -- both technooptimistic and technopesimistic -- and it tries to find the most suitable definition. People do not want to admit the cyborgization is not only vision of distant future but all of us are the cyborgs practically. What for the thesis deals with various cyborgization methods using in practice or developing to apply them in practice in a short time. The major focus is put to eyesight, the thesis gives a detailed description of refractive surgery, it develops very fast nowadays. The thesis also deals with controversial topic -- digital chips beneath skin -- and then it tries to find an answer to cyborgization is able to separate the society.

The purpose of this study was to assess the effects of refractive vision correction through laser surgery (LASIK & PRK) of adults of working age (22-55). This study examined and compared the symptoms of depression, stress perception, and self-esteem prior to surgery and one month after surgery, when sufficient healing has occurred. Research has shown that vision impairment has been reported to be one of the 10 most significant causes of disability in the United States, and, even though clinicians are encouraged to assess emotional response to vision loss, the psychological factors that that play a role in adjustment to vision loss have not been sufficiently studied.

This is a study on the prevalence of refractive errors and patients requiring refractive services at 15 eye clinics in the Amathole, Chris Hani, Joe Gqabi and OR Tambo District Municipalities of the Eastern Cape. This is an area characterised by extreme poverty where the cost of an eye examination and prescription spectacles remains financially unobtainable for most. Optometry services are provided mainly by private optometrists who service the small proportion of the population that can afford them. Adults and children remain house bound or are labelled as dull and unproductive simply because they don’t have access to an eye examination and a pair of spectacles. Purpose The purpose of the study is to identify patients with refractive errors and those requiring refractive services at the 15 eye clinics in the Eastern Cape. Another purpose is to describe the refractive services that are available to patients attending health facilities, where the eye clinics are conducted. Lastly, the purpose is to explore the possibility of nurses providing refractive services independently or under the supervision of optometrists to supplement the lack to refracting and dispensing services. Study Method A quantitative and qualitative non-experimental descriptive design was used. Research involved the analysis of Vision Care’s eye clinic records collected from 15 eye clinics from January 2010-June 2010. Semi-structured interviews were conducted with 30 nurses working at the 15 health facilities where the eye clinics were conducted using purposive sampling. The quantitative data was analysed using excel spreadsheets and graphs and qualitative data was analysed using coding and categorizing methods. Conclusion According to Vision Care’s data of the patients assessed, 19.2 percent had a refractive error and 54 percent of the patients required refractive services. It is estimated that 71.41 percent of the patients had a refractive error according to the optometrist. Although there were some organisations active in the eradication of cataracts, there was little healthcare available in the form of refraction services. xiv Patients needed to travel an average of 63.8kms to access refraction services against the backdrop of poor roads, poverty and unemployment. 28 out of 30 nurses either ‘strongly agreed’ or ‘agreed’ that nurses could be trained to perform refractions and dispense spectacles. 29 out of 30 nurses thought that this would have a positive impact on eye care. Further research is necessary to assess the feasibility of implementing a nurse operated refractive program and whether it should be within their scope of practice to refract and dispense spectacles.

Dans un contexte d’augmentation du nombre d’amétropes dans la population mondiale, et en conséquence, de l’accroissement du recours aux techniques de corrections chirurgicales, la compréhension et l’amélioration de celles-ci sont un enjeu crucial. Nous avons cherché à améliorer la prédictibilité de certains résultats postopératoires dans le cas d’un LASIK (Laser-Assisted In-Situ Keratomileusis), d’une PKR (Photorefractive Keratectomy) ou d'une chirurgie de la cataracte, et ainsi formuler des recommandations pratiques qui contribueraient au développement de stratégies de traitement davantage personnalisés. Pour cela, nous avons utilisé prospectivement des méthodologies de « contrôle de qualité » des chirurgies sur de larges échantillons de patients. Dans un premier temps, nous avons étudié la dynamique pupillaire dans le cadre de chirurgies au LASIK et notamment le rôle du centre pupillaire, point de référence important dans les stratégies de centrage. Nous avons également évalué la dynamique du diamètre pupillaire et les modifications du segment antérieur sur des yeux subissant une chirurgie de la cataracte. La seconde partie du travail s’est focalisée sur le rôle de l’épithélium dans la topographique cornéenne. Nous avons comparé les topographies spéculaires de l'épithélium et de la couche de Bowman sur des cornées saines et des cornées kératoconiques, présentant une myopie faible à modérée corrigée par PKR. Enfin, dans la dernière partie de notre recherche, nous nous sommes intéressés aux changements de paramètres anatomiques de l'oeil, des performances visuelles et de la qualité de vision subjective survenant dans un échantillon d’yeux myopes après un LASIK réalisé avec le laser WaveLight® Refractive Suite (Alcon® Laboratories Inc., USA)
While the number of ametropic eyes in the world’s population and consequently the use of surgical correction techniques is increasing, understanding and improving these techniques is a crucial issue. We sought to improve the predictability of certain postoperative results in the case of LASIK (Laser-Assisted In-Situ Keratomileusis), PRK (Photorefractive Keratectomy) and cataract surgery, and thus to formulate practical recommendations that would contribute to the development of more personalized treatment strategies. To achieve this objective, we have prospectively used "quality control" methodologies to assess surgeries performed on large samples of patients. First, we studied the pupillary dynamics in LASIK surgery and in particular the role of the pupillary centre, an important point of reference in the centration strategies. We also assessed the dynamics of pupillary diameter and anterior segment changes on eyes undergoing cataract surgery. The second part of the work focused on the role of the epithelium in the corneal topography. We compared specular topographies of the epithelium and Bowman's layer in healthy and keratoconus corneas with mild to moderate myopia corrected by PRK. Finally, in the last part of our research, we were interested in the changes in anatomical parameters of the eye, visual performance and subjective quality of vision occurring in a sample of myopic eyes after LASIK performed with the WaveLight® Refractive Suite (Alcon® Laboratories Inc., USA)

There has been widespread interest in corneal biomechanics over recent years, driven largely by the advancements in, and the popularity of refractive surgery techniques and subsequent concerns over their safety. Lately there has been interest into whether crosslinking, which is currently used for the treatment of keratoconus, could be developed as a minimally invasive technique to change the refractive power of the cornea by selectively changing the corneal biomechanics in specific regions to induce a shape change. Successful application of this technique requires a detailed understanding of corneal biomechanics and so far, little is known about the biomechanics of this complex tissue. The current lack of understanding can be mostly attributed to the absence of a suitable measurement technique capable of examining the dynamic behaviour of the cornea under physiological loading conditions. This thesis describes the development of a novel full-field, ex vivo, measurement method incorporating speckle interferometric techniques, to examine the biomechanics of the cornea before and after crosslinking in response to hydrostatic pressure fluctuations representative of those that occur in vivo during the cardiac cycle. The eventual measurement system used for the experiments detailed in this thesis incorporated; an Electronic Speckle Pattern Interferometer (ESPI), a Lateral Shearing Interferometer (LSI) and a fringe projection shape measurement system. The combination of these systems enabled the 3-dimensional components of surface displacement and the 1st derivative of surface displacement to be determined in response to small pressure fluctuations up to 1 mmHg in magnitude. The use of both ESPI and LSI together also enabled the applicability of LSI for measurement of non-flat surfaces to be assessed, and limitations and error sources to be identified throughout this work. To enable the measurement of corneal biomechanics, part of this thesis was concerned with the design of a bespoke loading rig. A chamber was designed that could accommodate tissue of both porcine and human origin. This chamber was linked to a hydraulic loading rig, whereby the cornea could be held at a baseline pressure representative of normal intraocular pressure and small pressure variations could be introduced by the automated vertical movement of the reservoir supplying the chamber. Experiments were conducted on a range of non-biological samples with both flat and curved surface topography, and both uniform and non-uniform mechanical properties, to determine if the measurement configuration was giving the expected measurement data and the loading rig was stable and repeatable. Following experiments on non-biological samples, a range of experiments were conducted on porcine corneas to develop a suitable testing methodology and address some of the challenges associated with corneal measurement, including transparency and hydration instability. During these investigations, a suitable surface coating was identified to generate an adequate return signal from the corneal surface, while not interfering with the response. Alongside this, the natural variation in the response of the cornea was investigated over the total experimental time, and a range of data was presented on corneas before and after crosslinking, which confirmed the suitability of the measurement methods for the assessment of crosslinking. Ultimately, a small sample size of six human corneas were investigated before and after crosslinking in specific topographic locations. From the experiments on human and porcine corneas, full-field maps of surface deformation have been presented, and a compliant region incorporating the peripheral and limbal areas has been identified as being fundamental to the response of the cornea to small pressure fluctuations. In addition to this, the regional effects of crosslinking in four different topographic locations on corneal biomechanics have been evaluated. From this, it has been demonstrated that crosslinking in specific regions in isolation can influence the way the cornea deforms to physiological-scale fluctuations in hydrostatic pressure and this could have implications for refractive correction.

Objetivo: Investigar as alterações biomecânicas da córnea de suínos induzidas pela confecção de lamelas pediculadas de diferentes espessuras pelo laser de femtossegundo. Métodos: Para a formação dos dois grupos, 12 olhos de porcos foram usados: lamelas pediculadas de 100 e de 300 micrômetros confeccionadas pelo laser de femtossegundo. Cada olho foi submetido aos seguintes exames, antes da criação das lamelas: topografia por rasterstereography, Ocular Response Analyzer (ORA), tomografia do segmento anterior por coerência óptica para a avaliação paquimétrica corneal e das lamelas criadas e sistema de velocidade de onda (SVO), que mede a velocidade de propagação de ondas acústicas entre dois transdutores posicionados na superfície corneal antes e imediatamente, após a feitura da lamela. O primerio passo foi desenhado para o estudo das diferenças em relação à histerese corneal, fator de resistência corneal, mudanças na curvatura e velocidade de propagação de onda acústica entre córneas com lamelas finas e espessas. Posteriormente, as lamelas foram amputadas, e as medidas do sistema de velocidade de onda foram repetidas. Resultados: A média de espessura das lamelas ± desviopadrão (DP) foi de 108,5±6,9 (8,5% da espessura total) e 307,8±11,5 m (22,9% da espessura total), para os grupos de lamelas finas e espessas, respectivamente (p< 0,001). Histerese corneal e o fator de resistência corneal não apresentaram diferença estatística, após a criação de lamelas finas (p = 0,81 e p = 0,62, respectivamente). Histerese corneal foi significantemente mais baixa, depois da confecção de lamelas mais espessas (8,0±1,0 para 5,1±1,5 mmHg para medidas pré e pós-operatórias, respectivamente, p = 0,003, diminuição de 36,25%) e fator de resistência corneal também mostrou significante diminuição nesse grupo, após o procedimento cirúrgico; valores médios pré e pós-operatórios de 8,2±1,6 e 4,1±2,5 mmHg respectivamente (p= 0,007), diminuição de 50%. A ceratometria média simulada apresentou maiores valores, após a confecção das lamelas mais espessas em relação ao pré-operatório (ceratometria pré e pós-operatória de 39,5±1 D e 45,9±1,2 D, respectivamente, p= 0,003). Para o grupo de lamelas finas, não houve diferença estatisticamente significante (ceratometria pré e pós-operatória de 40,6±0,6 D e 41,4±1,0 D, respectivamente, p=0,55). Em relação ao Sistema de Velocidade de Onda, após a criação das lamelas e sua amputação, houve diminuição da velocidade de propagação acústica, embora na maior parte das posições não fosse estatisticamente significante. Conclusão: Nas condições experimentais estabelecidas por este estudo, a criação de lamelas de maior espessura pareceu exercer efeito mais relevante sobre a biomecânica da córnea de suínos
Purpose: To study the impact of programmed flaps at two different thicknesses on the biomechanical properties of the swine corneas. Methods: Twelve pig eyes were enrolled in this study and were formed two groups: 100m and 300 m flaps performed with the femtosecond laser. Each eye had the following procedure before the flap creation: raster photograph topographic maps, Ocular Response Analyzer (ORA), Optical Coherence Tomography to measure the pachymetry and flap thickness and Surface Wave Velocity system which is a prototype system that measures sonic wave propagation time between two transducers positioned on the corneal surface before and after flap creation. This first step was designed to investigate the differences in respect to corneal hysteresis, corneal resistance factor, curvature change and ultrasonic wave propagation between the groups with thinner and thicker flaps. After this initial procedure, flap amputation was performed and new measurements with the surface wave velocity system were taken again. Results: Measured flap thicknesses averaged 108.5±6.9 (8.5% of the total cornea) and 307.8±11.5 m (22.9% of the total cornea) for thin and thick flap groups, respectively (p< 0.001). Hysteresis and corneal resistance factor did not change significantly after flap creation in the thin flap group (p = 0.81 and p = 0.62, respectively). With thicker flaps, both parameters decreased significantly from 8.0±1.0 to 5.1±1.5 mmHg (p=0.003, reduction of 36.25%) and from 8.2±1.6 to 4.1±2.5 mmHg, respectively (p = 0.007), reduction of 50%. Simulated keratometry values increased in the thick flap group (from 39.5±1 D to 45.9±1.2 D, p=0.003) after flap creation and not in the thin flap group (from 40.6±0.6D to 41.4±1.0D, p= 0.55). Regarding surface wave velocity analysis, the surgical procedures induced lower values in some positions although most of them did not present statistically different results. Conclusion: In this experimental model, thicker flaps seemed to have a greater effect on the biomechanics of the swinish cornea

La cirugía refractiva corneal corrige los errores refractivos modificando la curvatura de la córnea. Después de la cirugía de la miopía con técnica LASIK, se ha observado un aplanamiento central inesperado de origen biomecánico y un encurvamiento periférico. El objetivo de este trabajo fue estudiar la relación entre ambos fenómenos y otros parámetros oculares. Se realizó un estudio retrospectivo de una serie quirúrgica, utilizando las topografías tangenciales diferenciales. El encurvamiento se caracterizó mediante tres parámetros: incremento de potencia, diámetro de la zona de mayor valor (anillo) y ángulo del gradiente periférico. Un estudio prospectivo analizó su presencia post-ablación en cuatro tipos de modelos esféricos experimentales sin respuesta biomecánica. El encurvamiento periférico se situó entre la zona óptica y la zona de transición, con un ligero desplazamiento lateral debido al ángulo kappa. No se halló correlación con el aplanamiento central inesperado. Tiene una correlación positiva y significativa con el gradiente teórico y con la edad. En los modelos experimentales, se presentó un anillo de encurvamiento periférico
Corneal refractive surgery corrects refractive errors by modifying the corneal curvature. After myopia surgery with LASIK, a central unexpected flattening of biomechanical origin and a peripheral steepening have been observed. The aim of this work was to study the relation between both facts and other ocular parameters. A retrospective study of a surgical series was done using the tangential differential topography. Steepening was characterized by three parameters: increase of power, diameter of the zone of major value (ring) and the angle of the peripheral gradient. A prospective study analyzed post-ablation peripheral steepening in four types of spherical experimental models without biomechanical response. The peripheral steepening was placed between the optical zone and the transition zone, with a light lateral displacement due to angle kappa values. No correlation with the central unexpected flattening was found, whereas it has a positive and significant correlation with the theoretical gradient and with the age. In the experimental models, a ring of peripheral steepening was present.

Orientador: Luiz Carlos Pereira da Silva
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação
Made available in DSpace on 2018-08-18T01:45:50Z (GMT). No. of bitstreams: 1 Villar_FernandaSpada_M.pdf: 4737992 bytes, checksum: 3ce0cbb4f82fc2a7fd54013a9d3724f1 (MD5) Previous issue date: 2011
Resumo: Neste trabalho a propagação de transitórios de tensão dentro de uma rede coletora de parques eólicos marítimos foi estudada. Foram analisados especificamente os transitórios de tensão originados durante a energização do parque eólico, e foi modelado o efeito dos múltiplos pontos de reflexão na composição da forma de onda da sobretensão transitória. O momento de energização desperta interesse pois todos os transformadores localizados nos topos das torres, por estarem descarregados, se comportam como um ponto de circuito aberto, refletindo de volta para a rede 100% de qualquer onda de tensão viajante que incide sobre ele. As configurações de rede coletora escolhidas foram as comumente utilizadas em Parques Eólicos Marítimos atualmente pela Europa. Ainda, uma topologia alternativa que emprega a rede de cabos em estrela foi estudada. Para validação dos estudos analíticos e da modelagem desenvolvida foi utilizado o software PSCAD. A análise numérica dos coeficientes de reflexão e refração nos nós da rede coletora e de seu efeito na propagação dos transientes em questão mostrou que o efeito atenuador resultante de refrações consecutivas dentro da rede, no caso do coeficiente de refração menor que 1, tem grande importância, chegando a anular o efeito amplificador da interferência construtiva, decorrente da existência de múltiplos pontos de reflexão
Abstract: In this dissertation, the propagation of voltage transients inside a collection grid of Offshore Wind Parks (composed by cables) is studied. Mainly the transients generated during the WP energizing are analyzed, and the effect of the multiple reflection points in the composition of the overvoltage is modeled. The energizing moment is a special case to study because all the transformers at the towers top, being unloaded, behave like an open circuit and reflect 100% of the incident voltage travelling waves back to the grid. The grid configurations chosen are the commonly used in modern Offshore Wind Parks in Europe. Also an alternative layout, that uses the cables in a star grid, is studied. In order to validate the theory developed, simulations were made using the software PSCAD. The numerical analysis of the reflection and refraction coefficients in every node of the collection grid and its effect in the voltage transient's propagation showed that the attenuation effect, as a result of the consecutive refractions inside the grid in the cases where the refraction coefficient is smaller than 1, is important enough to cancel the amplification effect of the constructive interference, that happens due to the multiple reflection points.
Mestrado
Energia Eletrica
Mestre em Engenharia Elétrica

Important causes of dissatisfaction after cataract surgery are dysphotopsia (glare, halos, starbursts), requiring intraocular lens (IOL) exchange in 5.7% of cases. Optical parameters per se cannot explain why symptoms are different among patients, as no differences have been found in light scatter, aberrations, residual sphere and cylinder. Attempts to link optical outcomes and dysphotopsia have not proven an association between measurable aberrations and symptoms. This suggests the involvement of other mechanisms, possibly at the neural level. Because these symptoms tend to improve over time, it is thought that the brain adapts to those unwanted stimuli (neuroadaptation). In fact, our vision is determined by how the brain processes incoming retinal input, as vision involves “constructive” perception and not merely the analysis of an optically perfect image. Neuroplasticity is the ability of the brain to reorganize its connections in response to the changing patterns of inputs from the environment. Functional magnetic resonance imaging (FMRI) has opened an unprecedented opportunity for studying brain activity. We used FMRI to identify changes in neural activity patterns after multifocal IOL implantation over time and their relation with objective and qualitative aspects of visual function. We enrolled a cohort of patients implanted with multifocal IOLs after cataract surgery and age- and gender-matched healthy controls, without cataract or previous ocular surgery. Patients underwent functional MRI at post-operative intervals of 3 weeks and 6 months. Controls were evaluated at the same time intervals. Functional stimuli consisted in sinusoidal gratings with threshold contrast and a light source to induce disability glare. Subjective quality of vision and reading performance were assessed and wavefront analyses were conducted in both groups. To set up the experiment we designed a contrast assessment psychophysical task and a functional MRI task, created a proprietary magnetic resonance compatible LED frame with associated dimmer and an innovative psychophysical set up that allows contrast sensitivity evaluation under a glare source. We also developed the Portuguese version of the Radner Reading Tests (Radner-Coimbra Charts) to evaluate reading performance in our patients. With the first visit data (3rd week) we demonstrated the association between patient reported subjective difficulties and FMRI outcomes, independently of optical parameters and psychophysical performance. The increased activity of cortical areas dedicated to attention (frontoparietal circuits), learning and cognitive control (cingulate) and to task goals (caudate) likely represented the beginning of the neuroadaptation process to multifocal intraocular lenses. In addition, we investigated the relation between optical properties, visual function, subjective quality of vision and population receptive fields (PRF). PRF are the aggregate receptive field of the neurons within an FMRI voxel that respond to stimulation of a particular retinal location. Smaller PRFs reflect more fine-tuned visual processing, effectively increasing the spatial resolution of the visual system, while large PRFs reflect a coarser neural representation of visual space. We found that optical properties of the eye influenced PRF sizes. Aberrations of the visual system had a negative influence on visual cortical processing. Moreover, we reported the dissociation between subjective quality of vision and PRF sizes, indicating that patients with better cortical resolution may have improved perception of dysphotic phenomena, and consequently more quality of vision complaints, in spite of the improved optical quality. These findings complement the aforementioned results, concerning the absence of correlation between subjective quality of vision complaints and optical properties. Finally, using the same set up of the first study visit, we studied all study subjects five months later, to allow comparison between early results and those obtained after neuroadaptation is likely to be fully implemented. Patients no longer showed increased activity of cortical areas involved in visual attention, procedural learning, effortful cognitive control and goal oriented behavior at 6 months. There were no differences between visits in aberrations, Strehl ratio or modulation transfer function. There were significant improvements in questionnaire symptom scores, visual acuity and reading performance. The control group remained unchanged. In conclusion, our work contributed to identify that neuroadaptation to multifocal IOLS takes place initially through recruitment of visual attentional and procedural learning networks. Thereafter, a form of long-term adaptation/functional plasticity occurs, leading to brain activity regularization towards a non-effort pattern. Our neuroimaging findings are consistent with functional and questionnaire outcomes and are unrelated to optical properties, which reinforce the crucial adaptive role of higher-level brain regions in our perceptual construction of vision. Such information provides background knowledge for the identification of therapeutic targets and of intraocular lens characteristics that are more likely to trigger neuroadaptation circuits effectively and, hence, lead to practical clinical use.
As disfotópsias (brilhos, halos, riscos estrelados) são uma causa importante de insatisfação após cirurgia de catarata, levando à substituição da lente intraocular (IOL) implantada em 5.7% dos casos. Os diversos parâmetros óticos não explicam per se as diferenças nas queixas subjetivas dos doentes, já que não são encontradas diferenças em termos de dispersão da luz, aberrações, esfera ou cilindro residuais. Não existe uma associação clara entre aberrações óticas e sintomas, o que sugere o envolvimento de outros mecanismos, provavelmente a nível neuronal. Atendendo a que as disfotópsias tendem a melhorar ao longo do tempo, pensa-se que o cérebro se adapta à presença destes estímulos indesejados (neuroadaptação). De facto, a nossa visão é determinada pela forma como o cérebro processa estímulos provenientes da retina, já que a visão envolve uma perceção construtiva e não apenas a receção de uma imagem oticamente perfeita. Neuroplasticidade é, justamente, a capacidade de o cérebro reorganizar as suas conexões em resposta às modificações provenientes do exterior. A ressonância magnética funcional (FMRI) permite estudar a atividade do cérebro in vivo. No presente estudo recorremos à FMRI para identificar modificações nos padrões de atividade neuronal após implante de lentes multifocais, ao longo do tempo, bem como a sua relação com aspetos objetivos e qualitativos de função visual. Avaliámos uma coorte de doentes submetidos a cirurgia de catarata com implante de lentes multifocais e controlos saudáveis, ajustados à idade e ao género, sem catarata nem antecedentes cirúrgicos oftalmológicos. Os doentes foram submetidos a FMRI 3 semanas e 6 meses após a cirurgia. Os controlos foram examinados nos mesmos intervalos temporais. O estímulo funcional consistiu em riscas sinusoidais com contraste limiar e uma fonte de luz para induzir brilhos. As aberrações óticas, a qualidade de visão subjetiva e o desempenho na leitura foram avaliadas em ambos os grupos. Para a execução da tarefa experimental procedemos ao desenho das tarefas de FMRI e psicofísica, criámos uma moldura de LED com reóstato compatível com ressonância magnética e um teste psicofísico inovador, que permite determinar o limiar de contraste sob fonte de luz. Desenvolvemos ainda a versão portuguesa do teste de leitura de Radner (Tabelas de Leitura de Radner-Coimbra). Os resultados obtidos demonstram uma associação entre as dificuldades reportadas pelos doentes e os dados de FMRI, independentemente dos parâmetros óticos. A maior ativação relativa de áreas corticais dedicadas à atenção (circuitos frontoparietais), aprendizagem e controlo cognitivo (córtex cingulado) e aos objetivos da tarefa (caudado) representam provavelmente o início do processo de neuroadaptação às lentes multifocais intra-oculares. Além disso, investigámos a relação entre propriedades óticas, função visual, qualidade de visão subjetiva e os campos recetores populacionais (PRF). Os PRF são o conjunto dos campos recetores dos neurónios de um voxel de FMRI que respondem à estimulação de determinado local retiniano. Campos mais pequenos refletem um processamento visual mais perfeito, aumentando a resolução espacial do sistema visual, enquanto PRF maiores refletem uma representação neuronal mais grosseira do espaço visual. Descobrimos que as propriedades óticas do olho influenciam o tamanho dos PRF. As aberrações do sistema visual têm um impacto negativo no processamento visual cortical. Adicionalmente, reportámos a dissociação entre qualidade visual subjetiva e tamanho dos PRF, indicando que doentes com melhor resolução cortical podem ter melhor perceção de fenómenos disfóticos, e, consequentemente, mais queixas no que respeita à qualidade visual, apesar da melhor qualidade ótica. Os resultados do estudo dos PRF complementam assim os achados previamente descritos, sobre a relativa independência entre qualidade de visão subjetiva e propriedades óticas do olho. Finalmente, usando a mesma metodologia empregue na primeira visita, avaliámos todos os participantes do estudo 5 meses depois, para permitir a comparação entre os resultados iniciais e os obtidos numa altura em que a neuroadaptação já estará implementada. Os doentes apresentam, na segunda visita, uma normalização das áreas ativadas preferencialmente na primeira visita (áreas de atenção, aprendizagem processual, controlo cognitivo e comportamento orientado para os objetivos). Não houve alterações significativas entre visitas no que respeita a aberrações óticas, rácio de Strehl ou função de transferência modular, apesar da melhoria significativa na pontuação dos questionários, acuidade visual e desempenho na leitura. O grupo controlo não apresentou alterações ao longo das visitas. Em conclusão, este trabalho contribuiu para estabelecer que a neuroadaptação às lentes multifocais intraoculares ocorre inicialmente através do recrutamento de redes neuronais ligadas à atenção e à aprendizagem processual. Estabelece-se uma forma de adaptação a longo prazo/ plasticidade neuronal, levando à normalização da atividade neuronal no sentido de um padrão de não-esforço. Os achados de neuroimagem são consistentes com a desemprenho funcional e com os resultados do questionário, independentemente das propriedades óticas, o que reforça o papel crucialmente adaptativo das áreas de alto-nível do cérebro na construção percetual da visão. Os conhecimentos assim obtidos proporcionam as bases para a identificação futura de agentes terapêuticos em casos de não adaptação e das características presentes nas lentes intra-oculares que mais eficazmente possam ativar circuitos de neuroadaptação, levando, assim, à sua aplicação na prática clínica.
Gabinete de Apoio à Investigação da Faculdade de Medicina de Coimbra

This thesis presents some of the changes occurring in the accommodative function and binocular vision after corneal and intraocular refractive surgery and also discusses some strategies to avoid potentially adverse complications associated with imbalance in the accommodative and binocular system. Aspects as accommodation, aging effect, neural and brain processing, pupil diameter, and binocular vision should be considered at pre- and post-surgery stages hence these factors may affect the vision quality and efficiency, and consequently patient’s satisfaction. Binocular and accommodative function are affected after refractive surgery and can have an impact on the outcomes of the surgical procedure, particularly in high astigmatisms, myopia or hyperopia, anisometropia, monovision correction, myopic overcorrection, pre-presbyopes and early presbyopic patients. Binocular vision and accommodative assessment could help the surgeon in terms of preoperative advice and should be considered for every patient undergoing any refractive procedure.
Esta tese apresenta algumas das principais alterações que ocorrem na função acomodativa e de visão binocular após cirurgia refrativa corneal e intraocular e também descreve algumas estratégias para evitar potenciais complicações adversas associadas com o desequilíbrio no sistema acomodativo e binocular. Aspetos como a acomodação, efeito da idade, processamento neural e processamento cerebral, diâmetro pupilar, e a visão binocular deve ser considerado nos estágios pré- e pós-cirurgia uma vez que estes fatores podem afetar a qualidade visual e consequentemente a satisfação do paciente. A função acomodativa e binocular são afetadas após cirurgia refrativa e podem ter um impacto nos resultados do procedimento, particularmente em astigmatismos elevados, hipermetropia ou miopia, anisometria, correção por monovisão, hipercorreção miópica, pacientes em idade presbiópica ou pré-presbiopes. As complicações binoculares e acomodativas podem ajudar o cirurgião em termos da avaliação pré-operativa e devem ser considerados em qualquer paciente submetido a qualquer cirurgia refrativa.

碩士
國防醫學院
航太醫學研究所
91
Introduction: Visual acuity of 20/20 may not be a good quality of vision. Best visual acuity could be reached by standard laser in situ keratomileusis (LASIK) in myopic subjects. However, the visual quality may not be satisfied. This study would investigate the high visual quality by an objective method (modulation transfer function, MTF) and a subjective method (contrast sensitivity function, CSF) after surgery. Methods: The twenty-five normal patients（free of systemic diseases and ocular diseases）were enrolled for this study. And strictly, only the subjects, whose uncorrected visual acuity (UCVA) were 20/20 or better after surgery, were qualified to be candidates of this study. A series of ophthalmologic examinations including UCVA、best corrected visual acuity (BCVA)、wavefront aberrometer、and CSF were performed before and at 1st week, 1st month, and 3rd month after the operation. LASIK operation was performed using a smart-beam, variable spot scanning (VSS) excimer laser, and was assisted by eye-tracker. (VISX STAR S3). Results : In subjects (n=25 eyes), the mean age was 34 ± 5.9 yrs (22 ~ 41yrs) and the pre-op refractive error (spherical equivalent) was -7.00 ± 1.8 diopters (D). The residual refractive error was stable at 1st month (-0.6 ± 0.5D ) after LASIK operation. The daytime CSF at 1.5 cycles per degree (cpd) and night-time CSF at 6, 12, and 18 cpd were significantly increased at 3rd month after LASIK treatment. MTF of all aberrations was significantly increased after surgery. However, the postoperative MTF of all aberrations was lower than the operative goal (only pre-op higher order aberrations). The change of higher order aberrations after LASIK operation made a decrease in MTF. And the postoperative lower order aberrations made more decreasing in MTF. Conclusions: This result suggested that the optic change of eyes can be determined objectively by MTF. We found the higher order aberrations were induced after surgery, especially in coma-like and spherical-like aberrations. These aberrations caused a decrease in optic quality. However, the improvement of night-time CSF at specific frequency was noticed at 3rd month after surgery. Therefore, the role of individual aberration in visual quality needs to be further explored.

No
All forms of corneal refractive surgery can sometimes cause an increase in optical aberrations and scattered light, which can affect visual performance. The purpose of this study was to develop a suitable test that was sensitive to retinal image degradation in subjects who have undergone excimer laser refractive surgery and that was also relevant to visual demands in commercial aviation. Methods: Assessment of the visual environment and the tasks involved in piloting a commercial aircraft formed the basis for the selection of the test parameters. The new contrast acuity assessment (CAA) test covers a functional visual field of ±5° and is based on minimum spatial vision requirements for commercial pilots. Results: Data measured in 100 normal subjects were used to define the `standard normal observer' and the range of variation for the parameters of the test. This approach makes it possible to quickly establish whether a given subject's performance falls within the range of the standard normal observer. The test is also administered under low ambient illumination since flying at night involves mesopic levels of light adaptation when the pupil size is large and the effects of aberrations and scattered light are therefore more pronounced. Conclusion: The results of the test are simple to interpret and reveal visual performance that falls outside the normal range as a result of either significant degradation of retinal image quality (caused by increased aberrations and scattered light) or abnormal processing of visual information in the retina and/or the visual pathway.

PURPOSE: To determine if there is a relationship between eyes with flat corneas (as defined by calculated postoperative keratometry values of <38D) undergoing either LASIK (Laser-assisted in Situ Keratomileusis), LASEK (Laser-assisted Subepithelial Keratectomy), or PRK (Photorefractive Keratectomy) corneal refractive surgery and loss of 1 or more lines of postoperative BCVA, and if there is an advantage to undergoing either LASIK or ASA in eyes meeting flat cornea criteria. METHODS: A retrospective analysis of 191 candidate eyes with calculated postoperative keratometry values <38D were identified and matched by manifest refraction and surgery type to 191 control eyes with calculated postoperative keratometry values ≥38D. Both candidate groups and control groups were further stratified into subgroups based on degree of calculated postoperative keratometry. Candidate subgroups: Subgroup 1a (K<35D), Subgroup 2a (K=35-35.99D), Subgroup 3a (K=36-36.99D), and Subgroup 4a (K=37-37.99D). Control subgroups: Subgroup 1b (K=38-38.99D), Subgroup 2b (K=39-39.99D), Subgroup 3b (K=40-40.99D) and Subgroup 4b (K≥41D). All patients had undergone corneal refractive eye surgery procedures LASIK, LASEK, or PRK at Boston Eye Group/Boston Laser in Brookline MA between December 2008 and November 2016. All LASIK flaps were created using the femtosecond laser IntraLase iFS60 Laser (Abbott Medical Optics Inc.). All surface ablation procedures were performed using the excimer lasers VISX STAR S4 IR Excimer Laser System (Abbot Medical Optics Inc.) or WaveLight EX500 Excimer Laser (Alcon Laboratories Inc.). Visual acuity outcomes measuring preoperative and postoperative BCVA and loss of BCVA were recorded as part of the patient’s medical chart and were statistically analyzed to determine correlations. RESULTS: Our data showed no significant differences between overall candidate (K<38D) and control (K≥38D) group mean preoperative BCVA (p<0.23) or mean postoperative BCVA (p<0.13). A total of 15 out of 191 (7.9%) candidate eyes lost 1 or more lines of BCVA in comparison to 23 total control eyes (12.0%) that lost 1 or more lines of BCVA postoperatively. When evaluating subgroup data, Candidate Subgroup 1a (K<35D) showed a significant (p<0.02) decrease in BCVA when compared to other candidate subgroups. Additionally, Control Subgroup 1b (K=38=38.99D) and Control Subgroup 2b (39-39.99D) showed a significant (p<0.001 and p<0.02 respectively) decrease in BCVA compared to other control subgroups. A total of 231 total candidate and control eyes underwent LASIK and a total of 151 total candidate and control eyes underwent ASA. Overall, 17 out of the 231 (7.4%) eyes undergoing LASIK lost BCVA compared to the 21 out of 151 (13.9%) eyes undergoing ASA that lost BCVA which was significant (p<0.04). CONCLUSION: This study did not find evidence to support that the overall flat cornea group (K<38D) lost postoperative BCVA when compared to a control group of eyes with normal keratometry values. However, our data indicated that when the candidate group was stratified by degree of corneal curvature, patients with very flat corneas (K<35D) may be at increased risk of losing BCVA though further studies are needed. Additionally, eyes undergoing ASA may be at increased risk of losing BCVA though further studies are needed.
2018-07-11T00:00:00Z

INTRODUCTION/PURPOSE: Billions of people world wide suffer from refractive errors requiring glasses, contact lenses, or other means of correction to enable them to see better. Many people seeking permanent means to correct their vision consider undergoing corneal refractive laser surgeries (CRLS), photorefractive keratectomy (PRK), laser-assisted subepithelial keratectomy (LASEK), or laser in situ keratomileusis (LASIK). These surgeries have been shown to improve vision, but are not without risks for complications intra-operatively and postoperatively. Few studies have looked at the long-term incidence of postoperative complications such as dry eyes and visual aberrations and the associated preoperative risk factors. It is the aim of this study to examine the long-term incidence of dry eyes and visual aberrations (starbursts, halos, glare) after CRLS, and assess for preoperative risk factors associated with the persistence of these symptoms after surgery. METHODS: This study consisted of 319 patients identified for undergoing PRK, LASEK, or LASIK, at Boston Laser between December 2009 and January 2014. The participants in this study completed a novel online questionnaire consisting of questions to assess dry eye and visual aberration symptoms, and included questions adapted from the Ocular Surface Disease Index (OSDI). Postoperative dry eye symptoms were measured based on the OSDI score and a new dry eye measurement score created for this study's questionnaire. Presence or absence of visual aberration symptoms postoperatively were measured based on a score created for this study and derived from the calculation of the OSDI score. Additionally, a retrospective chart review was conducted of the 319 participants' medical charts to gather and assess for preoperative risk factors related to the long-term incidence of both dry eye and visual aberration symptoms. RESULTS: Our data found a significant association (p < 0.05) that suggests a relationship between development of long-term dry eye symptoms and the following preoperative variables: pupil size, flap thickness, and dry eye risk assessment (including: Zone Quick test values ≤ 9.0mm, contact lens use, and dry eyes with and without contact lenses). No significant association (p > 0.05) was found between the novel dry eye score and the preoperative factors, but it did approach significance with two variables, necessitating further investigation: gender and actual ablation. No significance (p >0.05) was found in the association between the preoperative dry eye risk assessment and severity of postoperative symptoms as gathered using the OSDI score. Our data found a significant association (p < 0.05) that suggests an increased risk for development of long-term visual aberrations symptoms postoperatively with the following preoperative variables: cylindrical manifest refraction, flat K, and greater actual flap thickness. As well as identifying two other possible variables that approached significance requiring further investigation: steep K and preoperative visual aberrations risk (including: spherical manifest refraction ≥ -6.00, astigmatic manifest refraction ≥ -2.00, and pupil diameter ≥ 7.0). The data showed a significant association (p < 0.05) between postoperative symptom presence and the aforementioned preoperative visual aberrations risk. Our data showed no significance (p > 0.05) when comparing the difference between mean OSDI, dry eye, and visual aberration scores between participants grouped by years since surgery. DISCUSSION/CONCLUSION: Our data found a significant relationship between long-term dry eye risk after CRLS and preoperative pupil size, flap thickness, and dry eye risk assessment. Similarly the data also displayed a significant association between long-term visual aberration risk after CRLS and greater preoperative cylindrical manifest refraction, flat K, and flap thickness. These findings contribute to the risk factors identified in similar short-term follow-up studies, and support the need for increased research into the risk factors and long-term incidence of dry eyes and visual aberrations after CRLS. While the data showed no significance between participants grouped by years since surgery and reported postoperative symptoms, the OSDI mean scores did approach significance (p = 0.088), suggesting that further research with a greater survey population is required.

Wavefront-guided (WFG) laser in situ keratomileusis (LASIK) differs from conventional surgery by applying a refined algorithm for tissue removal, based on information from preoperative wavefront aberration data. Since the introduction of this technology, there have been few investigations comprehensively reporting outcomes, particularly for hyperopic treatments. This thesis aimed to determine the impact of myopic and hyperopic WFG LASIK on visual acuity, contrast sensitivity, higher order aberrations and subjective ratings, as well as determine the relationship between these outcome measures. Bilateral WFG LASIK was performed on 324 myopic eyes (162 subjects) and 62 hyperopic eyes (31 subjects). High contrast (HC) and low contrast (LC) best-corrected visual acuity (BCVA) and contrast sensitivity were assessed using ETDRS charts and vertical sinusoidal gratings, respectively. Higher order ocular aberrations were measured using a Shack-Hartmann wavefront sensor and analyzed across a 5.0 mm pupil. Subjective ratings were assessed using a closed-ended categorical questionnaire. Assessments were conducted prior to surgery and at three and six months postoperatively. WFG LASIK had minimal impact on BCVA and contrast sensitivity; however there was an impact on the magnitude and profile of higher order aberrations, which differed between the myopic and hyperopic groups. There was a greater increase in higher order aberrations for the hyperopic group, who also had a tendency to have lower visual outcomes and worse subjective ratings. Despite these results, there were no associations between subjective ratings and higher order aberrations, LC BCVA or contrast sensitivity for both groups and a clear understanding of the relationship between these outcome measures was not apparent. Factor analysis revealed a variety of factors that contributed to the outcome measures for this data set, with the three main factors being: subjective ratings, vision and optical quality. In conclusion, WFG LASIK had excellent outcomes in terms of visual acuity, contrast sensitivity, and subjective ratings, despite an increase in higher order aberrations compared with those found prior to surgery. Hyperopic outcomes were slightly worse than myopic outcomes. Further investigation is required to determine the impact of higher order aberrations on visual acuity, contrast sensitivity and subjective ratings, as well as the relationship between these measures.

M.Phil.
Cataracts have been identified as one of the leading causes of blindness, especially in the developing world. The only presently known effective treatment for this growing problem is surgical removal of the opaque lens followed by replacement with an artificial intra ocular lens. Newer methods have brought greater success, and greater costs. For people in the developing world, these newer methods are not always an option. Together with the increased cost, there is a growing demand because of this worldwide problem. This increased need for surgery has lead to the development of waiting lists in the state funded hospitals. To qualify for a cataract extraction in most state funded hospitals, a best visual acuity of 6/60 is required, compared to the 6/12 to 6/24 levels required in the industrial countries and private practices. With these levels of visual impairment in the developing world, many patients are left functionally blind for long periods of time until cataract extraction can be performed. Older methods such as extra-capsular cataract extraction are still being used in the developing world. This is mostly due to the increased density of the cataracts at the time when the extraction can be performed because of the long waiting time leading to further maturation of the cataract. This method requires a large corneal incision, which is normally closed with nylon sutures. With this method of surgery meticulous wound closure is very important, and in many cases surgically induced astigmatism is one of the unwanted consequences. It was therefore decided, for the purpose of this study, to use autokeratometric data to explore the refractive effects of two different methods of corneal wound closure following planned extra-capsular cataract extraction (ECCE). Astigmatism is a major problem associated with extra capsular cataract extraction, especially when the wound is closed by means of sutures. Studies by Minassian et al. (2001), Jacobi (2003) and Dowler et al. (2000) all show that newer methods of cataract extraction making use of smaller incisions and therefore fewer sutures show faster recovery and less astigmatism. These methods are however mostly restricted to private practice, and therefore potentially unsuited for use in developing countries. The type of material used for wound closure is another very important factor. Depending on the method of suturing wound gape and wound compression can cause increased amounts of astigmatism. Using a method of wound closure that would cause less traction on the cornea could therefore cause less of a problem postoperatively. Tissue adhesives such as Tisseel® fibrin glue could be such an alternative. Studies by Henrick et al. (1987), Kim and Kharod (2007) and Bhatia (2006) show that fibrin glue forms a watertight, non irritating wound while promoting the healing process by the cross linking of collagen fibres.

碩士
國立臺灣大學
臨床醫學研究所
94
Laser refractive surgery is performed by using Ar-F excimer laser to disrupt the inter-molecular bonding of corneal tissue and ablate the cornea, thereby changing the curvature and refractive power of anterior corneal surface. However, as soon as the spherical and cylindrical refractive errors are corrected by laser, higher-order aberrations of anterior corneal surface also result. This is due to the irregular change of anterior corneal surface by wound healing process or the laser treatment itself. The surgical and mechanical techniques of laser refractive surgery have been processing during the past decade. Photorefractive keratectomy (PRK) was preformed in the past, whereas laser in situ keratomileusis (LASIK) is used most often at present time. The laser beams also evolve from broad beams to flying spots and mixed spots. Since the laser refractive surgery itself induces the higher order aberrations of anterior corneal surface, these different surgical techniques and machines attribute differently to the higher-order aberration (HOA). In this study, we calculate the HOAs of anterior corneal surface by computerized corneal topography and calculating software. We then analyze the affecting factors of HOA changes after surgery, including surgical techniques (PRK vs. LASIK), laser machines (Summit Apex Plus, Allegretto Wave, Bausch & Lomb Technolas 217z, and VISX S4), age, attempted sphere correction, attempted cylinder correction, optic zone size, and transitional zone size. Besides, we use questionnaires to evaluate the visual quality and the extent of satisfaction of patients, and analyze the relationships with corneal surface HOA changes. As the result shows, all HOAs increased significantly after surgery by various techniques and machines. LASIK induced more trivial HOAs (the 5th and 6th orders) after surgery than PRK did. The diopters of spherical equivalent corrected were highly correlated with surgical-induced HOA changes. Patients with older ages had less HOA changes. The larger the treatment zone sizes (including optic zones and transitional zones), the less the surgical-induced HOA changes. Some flying-spot machines induced less coma-like aberrations, while no obvious differences of spherical-like aberrations and total HOAs between broad-beam machines and flying-spot ones were noted. The visual quality and the extent of satisfaction of patients correlated most strongly with spherical-like aberrations, then with total HOAs, and then with coma-like aberrations. In the future, we can try to improve the surgical techniques and the preciseness of laser machines according to these results. We hope our efforts can contribute to more perfect visions of future patients!

No
To determine whether Hartmann-Shack wavefront sensing detects differences in optical performance in vivo between poly(methyl methacrylate) (PMMA) and foldable acrylic intraocular lenses (IOLs) and between clear corneal and scleral tunnel incisions and whether optical differences are manifested as differences in visual performance. SETTING: Department of Optometry, University of Bradford, West Yorkshire, United Kingdom. METHODS: This study comprised 74 subjects; 17 were phakic with no ocular pathology, 20 had implantation of a Pharmacia 722C PMMA IOL through a scleral tunnel, 21 had implantation of an Alcon AcrySof IOL through a scleral tunnel, and 16 had implantation of an AcrySof IOL through a corneal incision. Visual acuity and contrast sensitivity testing, ocular optical quality measurement using Hartmann-Shack wavefront sensing, and corneal surface measurement with a videokeratoscope were performed in all cases. RESULTS: There were significant differences between groups in the total root-mean-square (RMS) wavefront aberration over a 6.0 mm pupil (F=3.91; degrees of freedom=3,70; P<.05) mediated at the 4th-order RMS, specifically spherical and tetrafoil aberrations. The PMMA-scleral group had the least aberrations and the AcrySof-corneal group the most. For a 3.5 mm diameter pupil, the total higher-order RMS wavefront aberration was not significantly different between the groups (P>.05). There were no differences between groups in corneal shape, visual acuity, or contrast sensitivity. CONCLUSIONS: Implantation of the spherical PMMA IOL led to a slight reduction in total wavefront aberration compared to phakic eyes. AcrySof IOLs induced more aberrations, especially spherical aberration. Corneal-based incisions for IOL implantation compounded this increase. Studies of the optical performance of IOLs in vivo should use wavefront sensing as the main outcome measure rather than visual measures, which are readily confounded by multiple factors.

Yes
Purpose To determine whether dizziness and falls rates change due to routine cataract surgery and to determine the influence of spectacle type and refractive factors. Methods Self-reported dizziness and falls were determined in 287 patients (mean age of 76.5 ± 6.3 years, 55% females) before and after routine cataract surgery for the first (81, 28%), second (109, 38%) and both eyes (97, 34%). Dizziness was determined using the short-form of the Dizziness Handicap Inventory. Six-month falls rates were determined using self-reported retrospective data. Results The number of patients with dizziness reduced significantly after cataract surgery (52% vs 38%; χ2 = 19.14, p < 0.001), but the reduction in the number of patients who fell in the 6-months post surgery was not significant (23% vs 20%; χ2 = 0.87, p = 0.35). Dizziness improved after first eye surgery (49% vs 33%, p = 0.01) and surgery on both eyes (58% vs 35%, p < 0.001), but not after second eye surgery (52% vs 45%, p = 0.68). Multivariate logistic regression analyses found significant links between post-operative falls and change in spectacle type (increased risk if switched into multifocal spectacles). Post-operative dizziness was associated with changes in best eye visual acuity and changes in oblique astigmatic correction. Conclusions Dizziness is significantly reduced by first (or both) eye cataract surgery and this is linked with improvements in best eye visual acuity, although changes in oblique astigmatic correction increased dizziness. The lack of improvement in falls rate may be associated with switching into multifocal spectacle wear after surgery.
This work was supported by The Dunhill Medical Trust(grant number SA14/0711).