Dissertations / Theses on the topic 'Anterior eye segment'

The thesis investigates methods of examining corneal biomechanics using non-contact tonometry and introduces novel techniques to investigate corneal material properties in vivo. A comprehensive systems analysis of the CorvisST (CST) and Ocular Response Analyser (ORA) was performed. Pressure sensors were used to characterisation the airflow produced by the CST and the ORA. Distinct differences were observed between the central airflow pressures between the two devices: the CST pressure was higher and of shorter duration. Scheimpflug high-speed imaging via the CST allowed components of the corneal deformation to be investigated and the development of a 3D deformation matrix (time, depth and spatial resolution) through tracing of the anterior and posterior corneal surface. Measures of whole eye movement (WEM) with CST were found to be robust. WEM demonstrated an asymmetric profile and a correction method was developed to address the corneal deformation matrix for this asymmetry. Novel methods for characterisation of intrinsic material characteristics of the cornea were developed using numerical and graphical analytical procedures. Application of these parameters was tested on enucleated porcine eyes across a wide range of manometry internal ocular pressure (MIOP). The dynamic E-Modulus was found to be most affected by MIOP change. To investigate the in vivo distribution and heterogeneity of the corneal biomechanics, a novel set-up allowed the mapping of corneal biomechanics across the cornea using the CST (central, paracentral, peripheral) and ORA (central, peripheral). Biometric and demographic grouping of subjects allowed detection of discriminating factors between individuals. The results suggest that the in vivo cornea of healthy human adults can be characterised as a viscoelastic, damped system for longitudinal strain and a highly oscillating system for lateral strain. The cornea is approximately homogenous for measures of rigidity and dynamic E-Modulus but other corneal material characteristics (longitudinal and lateral strain, hysteresis, damping and compressibility) demonstrated regional differences. The experimental design employed allowed for strict control of biometric and biomechanical intersubject variables, based on gold-standard techniques as well as newly-developed methods, thereby creating a normative database for future use.

Abstract In this thesis study, the primary structure of the human α1(XVIII) polypeptide was elucidated, its tissue distribution was studied, and the phenotypic changes in the mouse eye due to lack of type XVIII collagen in a knock-out mouse model were studied further. In addition, the consequences of simultaneous lack of both type XVIII and XV collagen were studied in a mouse model lacking both of these proteins. Two variant forms of human α1(XVIII) polypeptide were identified in this study, although, to date, a third form has also been characterized. The analysis of tissue distribution of the two polypeptide forms revealed differences in their tissue distribution, since the longest variant occurs prominently in the liver, while the short form is the major transcript in other tissues studied, e.g. in the kidney. The study of the type XVIII single null mouse eyes revealed abnormalities in the anterior eye segment in addition to the previously reported defects in the posterior eye part. In the type XVIII single null mice the iris was fragmented, pigment deposits could be seen in the pupil, and the pupillary ruff in the edge of a normal mouse iris was missing in these mice. The ciliary body was also abnormal, since the ciliary processes start to show regression in adult animals and eventually the basal infoldings of the non-pigmented ciliary body epithelia become flattened in the null mice. The intraocular pressure stabilizes to a lower level in adult mutant mice compared to controls, most likely reflecting the atrophied ciliary epithelia. The BM zones were also defective in the type XVIII null mouse eyes. The absence of an immunosignal with one of the antibodies detecting laminin γ2 chain in the type XVIII null mouse eyes may implicate conformational changes in the laminin γ2 chain due to lack of type XVIII collagen, and subsequently interaction between type XVIII collagen and laminin γ2 chain in normal mouse eye BMs. The study of the type XVIII and XV double null mice revealed that these mice were viable and fertile and had no major additional abnormalities compared to both single null mice. However, the regression of hyaloid capillaries (vasa hyaloidea propria, VHP) was studied in these mice, and a slight delay in the detachment of these vessels from the retina was noticed. Thus, the two collagens do not function entirely independently from each other. The studies with type XVIII collagen single null mice indicate that in addition to the posterior eye phenotype, this collagen is needed for the normal structural integrity of the anterior eye segment and basement membranes of the eye. The mouse model lacking both type XVIII and type XV collagen indicates that the roles of the two collagens are essentially diverse, although a slight compensatory effect was observed in the detachment of the hyaloid capillaries from the retina.

Over the last two decades, depletion of stratospheric ozone has increased the flux of ultraviolet radiation (UVR) at the surface of the earth and the cumulative effect of UVR has become an important aspect of UV-induced eye damage. Epidemiological studies generally assess the chronic, low dose UVR exposure conditions while the laboratory animal experiments usually examine the acute response to high dose exposures. Thus, the study conditions are dissimilar and we are not free to assume that the two variant experimental settings necessarily trigger the same damage or repair mechanism. In order to correlate the results obtained from both experimental settings, laboratory studies of repeated UVR exposures under specific experimental design need to be conducted. The purpose of the present study was to focus on the comparison of the effects of single and repeated UVR-B exposures of the same overall doses on the metabolic profile of the anterior segment of the rabbit eye.

Rabbit eyes were exposed to single (312 nm, 3.12 J/cm²) or repeated (312 nm, 3 x 1.04 J/cm²) UVB irradiations and corneal, aqueous humour and lenticular samples were analysed by NMR spectroscopy. Special grouping patterns among the tissue samples and the relative percentage changes in particular metabolite concentrations were evaluated using advanced statistical methods (Principal component analysis, One-way ANOVA, Independent sample t-test).

The metabolic profiles of UVB irradiated and control samples were significantly different. Especially, alterations in the concentrations of antioxidants (ascorbate, GSH), compounds related to sugar metabolism (glucose, lactate), osmolytes (taurine, hypo-taurine, myoinositol, scylloinositol), choline-containing compounds (choline, phosphocholine) and amino acids were observed. A substantiall additivity of the repeated UVR-B exposures was revealed.

For the first time, a comparison of the effect of a single and repeated UVR exposure of the same overall dose on the metabolic profile of rabbit eye was conducted and described. This study reveals the cumulative effect of repeated UVB irradiation on the anterior segment of the rabbit eye and shows that even a 48 hours interval between subsequent UVR-B exposures is not sufficient for the healing process to restore normal metabolic status in the anterior segment of the rabbit eye.

Purpose: Assess the relationship between tear film drying and sensation between blinks. Methods: MATLAB sampled a slitlamp video camera, a potentiometer and a microphone while subjects kept one eye open for as long as possible. 23 subjects rated the intensity of the ocular sensation while video and voice data were collected simultaneously. The tear drying on the cornea was measured. Results: The sensation was triphasic. Two linear functions described the latter 2 parts of the data (r ≥ 0. 95). The correlation between TBUT and the elbow in the time-discomfort function was 0. 72. Extent of tear film drying was linearly correlated to time (median correlation = 0. 88). The correlation between the discomfort elbow and image elbow was 0. 93 with single data pair for each subject. Analysis of sensation characteristics showed significant differences between itching and burning for both intensity and time (p = 0. 03 and p = 0. 02 respectively). Conclusions: Simultaneous recording of ocular surface appearance, discomfort intensity and attributes of sensation provide novel information about the development of discomfort during ocular surface drying. The rapid increase in discomfort proceeding blinking has been quantified and the relationship between the time course of drying and discomfort is elucidated.

INTRODUÇÃO: O glaucoma de ângulo fechado é reconhecido como uma das principais causas de cegueira mundial. A iridotomia representa o tratamento de eleição nos casos com fechamento angular primário, entretanto, este procedimento pode não ser suficiente para proporcionar abertura do ângulo irido-corneano, controle da pressão intra-ocular (PIO) e estabilização do processo da lesão glaucomatosa. O presente estudo tem como objetivo avaliar a morfologia do segmento anterior do olho em uma amostra de pacientes brasileiros, e realizar uma comparação entre olhos normais (sem sinais de fechamento angular prévio) e olhos com ângulos oclusíveis, antes e após a realização da iridotomia. MÉTODOS: Realizou-se um estudo prospectivo observacional tipo caso-controle em pacientes da Clínica Oftalmológica do HC - FMUSP, onde 40 olhos com ângulos oclusíveis (grupo caso) e 27 olhos normais (grupo controle) foram examinados durante o período de agosto de 2003 a dezembro de 2004. Os pacientes do grupo controle foram pareados por idade, sexo e raça. Os exames de gonioscopia e biometria ultra-sônica foram utilizados para comparar os 27 olhos normais com os 40 olhos com ângulos oclusíveis, antes e após a realização da iridotomia. A biometria ultra-sônica mediu o comprimento axial do olho (CAX), a profundidade da câmara anterior (PCA) e o diâmetro ântero-posterior do cristalino (DAPC). Os 27 olhos do grupo controle foram comparados, através da biomicroscopia ultra-sônica, antes e após a iridotomia com os 31 olhos do grupo caso, que não apresentavam goniosinéquias no quadrante inferior. As imagens da UBM foram obtidas em cortes radiais sobre típicos processos ciliares, no claro e no escuro. A distância da abertura angular a 500?m do esporão escleral (DAA500), profundidade da câmara anterior (PCA-UBM), distância do trabeculado aos processos ciliares (DTPC), espessura da íris a 500?m do esporão escleral (EI500) e distância do esporão escleral à inserção da íris (linha X) foram medidas nas imagens da UBM obtidas às 6 horas. As freqüências de processos ciliares longos sem sulco ciliar e fechamento angular aposicional no escuro também foram determinadas nessas imagens. RESULTADOS: Os parâmetros morfológicos dos 27 olhos do grupo controle apresentaram diferenças significativas quando comparados com os 40 olhos do grupo caso. Os olhos normais apresentaram ângulo irido-corneano mais aberto, menor DAPC e maiores CAX e PCA. Nas imagens da UBM os 27 olhos normais apresentaram maior DAA500, PCA-UBM, linha X, e também, maior DTPC que os 31 olhos com ângulos oclusíveis (651 ± 119 ?m e 508 ± 116 ?m; p < 0.001); porém, a EI500 não apresentou diferença significativa entre os dois grupos. Após a realização da iridotomia foi observado uma abertura significativa do seio camerular, e uma diminuição da freqüência de fechamento angular aposicional nas imagens da UBM obtidas no escuro (28/31 para 16/31). Processos ciliares longos sem sulco ciliar foram observados em 61% (19/31) dos olhos do grupo caso após a iridotomia e em 33% (9/27) dos olhos do grupo controle. CONCLUSÃO: A presença de processos ciliares longos sem sulco ciliar foi um achado comum não somente nos olhos com ângulos oclusíveis como também nos olhos normais. No entanto, nos olhos do grupo caso, os processos ciliares estavam localizados, em média, numa posição mais anterior. Após a iridotomia, mais da metade dos olhos com ângulos oclusíveis continuaram apresentando fechamento angular aposicional na UBM. Os valores preditivos da presença de fechamento angular aposicional (associada ou não a processos ciliares longos sem sulco ciliar) na detecção de pacientes sob risco de apresentarem episódios de fechamento angular precisam ser avaliados em estudos futuros
Introduction: Angle closure glaucoma is emerging as one of the leading cause of worldwide blindness. Laser iridotomy (LI) has been proposed as first line therapy for patients with angle closure, however this procedure may not be effective opening the irido-corneal angle, controlling intra-ocular pressure (IOP) and halting glaucoma progression in all cases. Our study aimed to evaluate anterior segment morphology on a cohort of Brazilian patients comparing normal eyes (no signs of angle closure) to angle closure eyes before and after LI. Methods: In this prospective observational case control study, performed from August of 2003 to December of 2004, we evaluated 40 angle closure eyes and 27 normal control eyes with no signs of angle closure at clinical exam, paired by age, race and gender. We used gonioscopy and A-scan biometry to compare anterior segment morphology of 27 normal control eyes to 40 angle closure eyes of patients from our service, before and after LI. We also used ultrasound biomicroscopy (UBM) exam, to compare 27 normal control eyes to 31 of 40 angle closure eyes with no goniosynachiae at the inferior quadrant evaluated by gonioscopy, before and after LI. Immersion 50-MHz high-frequency ultrasound transducer was used to obtain UBM images in radial scans through a typical ciliary process, in both standard light and dark conditions. A-scan biometry measured axial length (AXL), anterior chamber depth (ACD) and lens thickness (LENS). The angle opening distance at 500?m from the scleral spur (AOD500), trabecular ciliary process distance (TCPD), iris thickness at 500?m and the distance from scleral spur to iris insertion (line X) were measured at UBM images obtained at the inferior quadrant. The frequency of appositional angle closure and the presence of long ciliary process with no ciliary sulcus were also evaluated at UBM images. Results: At gonioscopy and A-scan biometry exam, 27 normal eyes had a significant wider iridocorneal angle opening, a thinner LENS and a greater AXL, ACD than angle closure eyes. At UBM exam, 27 normal control eyes had an significant wider AOD500, line X and also, a longer TCPD than angle closure eyes (651 ± 119 ?m vs. 508 ± 116 ?m; p < 0.001); however no differences were observed in iris thickness between the two groups. After LI, we observed a significant irido-corneal angle opening and the number of angle closure eyes with UBM appositional angle closure in dark condition decreased from 28/31 to 16/31. A long ciliary processes with no ciliary sulcus were observed in 61% (19/31) of angle closure eyes after LI, and also in 33% (9/27) of normal control eyes. Conclusion: A long ciliary processes and absence of ciliary sulcus were a quite common finding not only in angle closure eyes, but also in normal control eyes. However, ciliary processes were located more anteriorly in angle closure eyes. On this cohort of Brazilian patients, more than half of studied eyes submitted to LI maintained UBM appositional angle closure. Whether this apposition with or without long ciliary process and absence of ciliary sulcus detected at UBM images after LI is associated to further goniosynachiae formation and/or loss of IOP control remains to be evaluated

Le but de ce travail a été d'étudier les différents effets microscopiques et macroscopiques susceptibles de nous aider à améliorer les procédures de chirurgie oculaire assistée par les lasers à impulsions ultra-courtes ; plus particulièrement en kératoplastie (greffe de cornée), qui nécessite des systèmes lasers opérationnels dans les tissus pathologiques et donc de diffusant fortement la lumière. Antérieurement, le groupe Optique Photonique Santé (OPS) du Laboratoire d'Optique Appliquée (LOA) a identifié 1650 nm comme étant une longueur d'onde optimale à laquelle les processus de diffusion de la lumière à l'intérieur de la cornée pathologique sont minimisés. Au cours de cette thèse, trois tâches principales ont été abordées. Un système laser à impulsions ultra-courtes à base de cristaux optiques non linéaires a été mis au point, optimisée par rapport aux exigences de chirurgie oculaire au laser, et entièrement caractérisé. Le montage achevé est compact, robuste, simple et potentiel-lement apte à un usage en clinique. En collaboration avec un groupe de l’IESL- FORTH (Iraklion, Grèce) et avec la parti-cipation d'un ancien doctorant du groupe, nous avons étudié l'interaction des impulsions ultra-brèves avec de l'eau, une solution de collagène (type I) et des cornées de porcs. Les données sur les interactions laser-tissu sont précieuses car la dynamique d'interaction est habituellement uniquement documentée pour l'eau; nos résultats aide-ront à élaborer un modèle spécifique de tissu pour le processus d'interaction. Nous avons étudié l'interaction entre les impulsions laser et les effets causés sur des cellules vivantes de l'endothélium cornéen. La préservation de la viabilité des cellules endothéliales est cruciale, notamment pour les routines de kératoplastie spécifiques exigeant des incisions à proximité de l'endothélium ; la viabilité des cellules endothéliales compromise – probablement causée par les effets des ondes de choc générées par claquage optique et la formation de bulles – peut conduire à un échec de l'interven-tion chirurgicale. Des jeux de paramètres « saufs » concernant l'énergie d'impulsion et de la géométrie de l'incision doivent être définis. Nous avons ainsi exploré les valeurs maximales autorisées de l'énergie de l'impulsion à une quelconque distance donnée des cellules endothéliales et les distances minimales pour les énergies d'impulsions données, et estimé les amplitudes des ondes de choc associées
He goal of this work was to study different microscopic and macroscopic effects that will ultimately help us to improve procedures in eye surgery assisted by ultrashort pulse lasers and most notably keratoplasty (corneal grafting), which requires laser systems which are operational in pathological and therefore strongly light scattering tissue. Previously, the Optique Photonique Santé (OPS) group at the Laboratoire d'Optique Appliquée (LOA) had identified 1650 nm as an optimum wavelength at which light scattering processes inside the pathological cornea are minimised. During the present thesis, three main tasks have been addressed. An ultrashort pulse laser system based on non-linear optical crystals has been developed, optimised with respect to the requirements of laser eye surgery, and fully char-acterised. The finished set-up is compact, robust, simple and potentially qualified for clinical use. In collaboration with a group at IESL-FORTH (Iraklion, Greece) and with the participation of a previous PhD student of the group we have studied the interaction of ultrashort pulses with water, collagen (type I) solution and porcine cornea. Data on laser-tissue-interaction is precious because the interaction dynamics is usually only documented for water; our results will help to develop a tissue-specific model for the interaction process. We have investigated the interaction of the laser pulses and the effects it causes with live cells in the corneal endothelium. The preservation of endothelial cell viability is crucial notably for specific keratoplasty routines which require incisions close to the endothelium; compromised endothelial cell viability – which is likely caused by the effects of shock waves generated by optical breakdown and bubble formation – may lead to a failure of the surgical intervention. “Safe” sets of parameters concerning pulse energy and incision geometry need to be defined. We explored the maximum permitted pulse energy values at any given distance to the endothelial cells and mini-mal distances for given pulse energies and estimated the associated shock wave amplitudes

Une des applications de l’échographie médicale est celle de l’ophtalmologie qui pose de nombreux problèmes spécifiques liés en partie à la faible dimension de l’oeil et à la précision importante que requièrent les mesures intraoculaires. En effet, avec le développement de la chirurgie réfractive qui regroupe ensemble des techniques capables de corriger les erreurs de réfraction et l’avènement des implants intraoculaires, le chirurgien ophtalmologiste est amené à surveiller la tolérance et les effets secondaires de ces implants sur les structures du segment antérieur. L’échographie à haute fréquence apporte la résolution suffisante pour cette tâche. Cependant, le développement de l’échographie 3D permet une extension des applications ophtalmologiques notamment pour le dimensionnement des implants en préopératoire. La modélisation 3D du segment antérieur permet d’étudier le comportement des implants et surtout de dessiner à terme un implant « sur mesure » pour le patient. C’est dans ce contexte que nous présentons une méthode originale de segmentation et de reconstruction 3D du segment antérieur par échographique haute fréquence en utilisant l’ajustement de modèles 3D. Nous utilisons un système échographique 3D de type main-libre, composé d’une sonde échographique haute fréquence, et d’un module de localisation actif comprenant une caméra et des marqueurs infrarouges. Ce système échographique 3D nous permet d’obtenir des images avec des informations de positionnement dans l’espace tridimensionnel associées. Nous avons ainsi pu mettre en place toute une chaîne d’acquisitions et de traitements des images échographiques. Nous créons, à partir d’images échographiques du segment antérieur oculaire, des modèles de référence 3D réalistes. Nous proposons ainsi une méthode d’ajustement de modèles 3D de référence sur des données 3D échographiques via l’utilisation de l’algorithme de recalage ICP. Nous avons également sélectionné et adapté différentes méthodes pour l’évaluation de l’approche de reconstruction proposée. Ces méthodes permettent de mettre en valeur la précision de ces reconstructions
Ophthalmology is one of the clinical application fields of ultrasound imaging, for which numerous specific issues arise, related in part to the eye’s small anatomical dimensions combined with the high level of accuracy requirements associated with intraocular measurements. Indeed, since the development of refractive surgery including all the techniques dedicated to the correction of refractive errors, as well as the emergence of intraocular lens (IOL), ophthalmic surgeons have to monitor overall acceptance as well as secondary effects related to these implants on the structures of the anterior eye segment. High frequency ultrasound imaging provides the required spatial resolution for this task. However, the development of 3D ultrasound imaging allows for the development of new applications in ophthalmology, for instance pre-operative dimensioning of the lens. 3D modelling of the anterior eye segment therefore allows studying the IOL behaviour and may help designing future personalized IOL tailored for each patient. Within this context, we present an original 3D segmentation and reconstruction method based on 3D models registration, dedicated to the anterior eye segment acquired in high frequency ultrasound imaging. We used a 3D ultrasound free-hand acquisition system, composed of a high frequency ultrasound probe and a localization module based on a camera and infrared markers. This 3D ultrasound system provides images along with associated 3D spatial positioning information. We were therefore able to develop an entire ultrasound images acquisition and processing chain. This allowed us creating realistic reference 3D models from sequences of ultrasound images of the anterior eye segment. We thus propose a method based on the iterative closest point (ICP) algorithm for the registration of the 3D reference models to 3D ultrasound acquired data. We have also selected and adapted various methods for the evaluation of the proposed reconstruction process. These methods highlight the accuracy of the obtained reconstructions

The eye contains closely related but widely different tissues, offering a unique opportunity to investigate the phenotype and function of monocyte-derived cell populations within functionally unique microenvironments in a single complex organ. The uveal tract and retina contain rich networks of immune cells that reside and traffic through the eye, these cells having been implicated in various ocular inflammatory processes and immune-mediated diseases. One such inflammatory condition is human posterior uveitis, an autoimmune disease mainly affecting the retina. As current treatments for posterior uveitis only serve to slow down disease progression, studies using animal models, namely, experimental autoimmune uveoretinitis (EAU), have focused on determining the key cellular and molecular mediators involved in disease initiation in order to expand the potential for novel therapeutic applications. The overall purpose of experiments in this thesis was to explore monocyte-derived cell populations of the uveal tract and retina, this being achieved by utilising a novel transgenic mouse model. Cx3cr1gfp/gfp transgenic mice on both BALB/c and C57Bl/6 backgrounds contain an enhanced green fluorescent protein (eGFP) encoding cassette knocked into the Cx3cr1 gene, disrupting its expression but facilitating GFP expression under the control of the Cx3cr1 promoter. Heterozygous (Cx3cr1+/gfp) mice were generated by crossing Cx3cr1gfp/gfp mice to wild-type (WT) mice. This transgenic model allowed for the exquisite visualisation of Cx3cr1-bearing monocyte-derived dendritic cells (DC) and macrophages in ocular tissues, whilst also enabling the investigation of a potential role for Cx3cr1 in recruiting monocyte-derived cells to the eye in steady-state and inflammatory conditions.

Corneal endothelial development is an intricate process driven by finely tuned gene expression. Its formation is necessary for the continued normal development of the anterior segment of the eye. The presence of an inductive lens able to secrete factors such as TGFβ2 as well as the expression of Foxc1 and Pitx2 is essential to corneal endothelial development, as in the absence of any of these; the corneal endothelium fails to form. Corneal endothelial development begins as peri-ocular mesenchyme (POM) cells migrate into the space between the lens and surface ectoderm at E11.5. From E12.5, these cells begin to transition from a mesenchymal to an epithelial/endothelial (MET) phenotype, differentiating into a monolayered endothelium by E15 characterised by inter-cellular junctions. To study the initial process of development, immortalised POM cell lines from E12.5 and E13.5 embryos were used. Expression of the key genes, the transcription factors, Foxc1 and Pitx2 and two genes involved in EMT/MET, Slug and Tsc22, were analysed at these stages to establish the developmental norm. The effect of the lens on these expression levels was then determined. To establish whether TGFβ2 is the lens secreted signal responsible for gene expression changes, cells were subjected to TGFβ2 treatment. In all these experiments, the role of Foxc1 in regulating gene expression was determined by Foxc1 overexpression and knockdown. The effect of the lens on cellular proliferation and on the expression and cellular arrangement of N-cadherin, a junction protein was also determined. The results showed that, at E12.5, the lens downregulates Foxc1 and Pitx2 expression, is a potent inducer of Tsc22 expression and is required for maintaining Slug levels. TGFβ2 was shown to play a role in Foxc1 and Pitx2 downregulation. Analysis suggests that Tsc22 expression is responsive to lens signals, but that TGFβ2 is not the signal responsible for its downregulation between E12.5 and E13.5. The lens has no effect on Slug expression in the presence of Foxc1, but when Foxc1 is silenced, Slug is induced. Thus, Foxc1 plays a crucial regulatory role in Slug expression. At E13.5, as differentiation is initiated, Foxc1 expression remains responsive to the lens and to TGFβ2. Pitx2 expression is still induced by the lens but, at this stage, TGFβ2 does not play a part in Pitx2 regulation suggesting involvement of other unknown lens secreted signals. Other lens secreted signal/s were also shown to downregulate Tsc22 and Slug at this stage. The lens was implicated in MET as it was shown to have an effect on N-cadherin localisation in 3-dimensional culture. E12.5 Spheroids exposed to E6 lenses formed a distinct lattice arrangement of N-cadherin compared to the uniform distribution in control cells. Although the 13.5 control cell aggregates also showed a lattice framework, it was more pronounced in the lens treated cells. The transcriptional role of Foxc1 was determined by overexpression and knockdown experiments where Foxc1 overexpression and knockdown upregulated Tsc22 and downregulated Pitx2 and Slug at E12.5. At E13.5, Pitx2 was downregulated and Slug was upregulated in response to aberrant expression of Foxc1. This was illustrative of the sensitivity these genes have to Foxc1 expression during development. It is known that the presence of a functioning lens and Foxc1 are essential for proper development of the corneal endothelium, which in turn is necessary for normal eye development. The understanding of the precise molecular mechanisms required for corneal endothelial development and the processes requisite for cell proliferation and differentiation has important consequences for providing further insight into the pathophysiology of anterior segment dysgenesis and glaucoma. Previous studies suggest that stem-cell like qualities are conferred in cells undergoing EMT. Such an investigation may lead to application in regenerative medicine such as the bioengineering of corneal tissue.
Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2013.

D.Phil. (Optometry)
An important issue in the quantitative analysis of optical systems is, for example, the question of how to calculate an average of a set of eyes. An average that also has an optical character as a whole and is representative or central to the optical characters of the eyes within that set of eyes. In the case of refraction, an average power is readily calculated as the arithmetic average of several dioptric power matrices. The question then is: How does one determine an average that represents the average optical character of a set of eyes, completely to first order? The exponential-mean-log transference has been proposed by Harris as the most promising solution to the question of the average eye. For such an average to be useful, it is necessary that the exponential-mean-log-transference satisfies conditions of existence, uniqueness and symplecticity, The first-order optical nature of a centred optical system (or eye) is completely characterized by the 4x4 ray transference. The augmented ray transference can be represented as a 5x5 matrix and is usually partitioned into 2x2 and 2x 1 submatrices. They are the dilation A, disjugacy B, divergence C, divarication D, transverse translation e and deflection 1t. These are the six fundamental first-orders optical properties of the system. Other optical properties, called derived properties, of the system can be obtained from them. Excluding decentred or tilted elements, everything that can happen to a ray is described by a 4x4 system matrix. The transference, then, defines the four A, B, C and D fundamental optical properties of the system…

The proper organization and differentiation of the anterior segment is pivotal for normal eye development. Neural crest-derived POM cells are key contributors to correct anterior segment formation, differentiating to form the monolayered corneal endothelium. Mice with homozygous null mutations in the forkhead transcription factor gene, Foxc1, fail to develop a proper corneal endothelium stabilized by adherens junctions, with the endothelium adhering to the lens, preventing anterior chamber separation. The aim of this study was to evaluate the interaction between Foxc1 and the adherens junction protein, N-cadherin, as well as an associated gene, Msx1, during key stages in corneal endothelium development. Foxc1 was over-expressed in E12.5 and E13.5 POM cells and qPCR was carried out to determine the effect of Foxc1 on N-cadherin and Msx1 gene expression. Data showed over-expression of Foxc1 in wildtype E12.5 and E13.5 POM cells to cause significant fluctuations in N-cadherin and Msx1 expression (p < 0.05). POM cells were then transfected with a Foxc1 knock-down plasmid or the Foxc1 overexpression plasmid to evaluate the effect of Foxc1 on N-cadherin protein expression by Western blot analysis, however, these results were inconsistent with the gene expression analyses with no significant differences in N-cadherin expression detected. N-cadherin protein expression and localization was then further assessed by means of immunocytochemistry (ICC) and confocal microscopy in monolayer and hanging-drop POM cell cultures. Both qPCR and confocal microscopy data showed consistency, indicating increased amounts of N-cadherin in E12.5 cells relative to E13.5 cells, with membrane-bound N-cadherin showing a clear lattice-work pattern in hanging drop culture. Foxc1 over-expression/knock-down studies on E12.5 and E13.5 POM cells together suggest that N-cadherin is transcriptionally regulated by Foxc1 and that Foxc1 has a threshold level at which it is able to exert control over N-cadherin in POM cells. Foxc1 expression is therefore essential in establishing N-cadherin adhesion junctions in the corneal endothelium. Preliminary data also suggests that Msx1 may directly interact with Foxc1 in POM cells, however, further studies must be undertaken to verify and establish the effects of Foxc1/N-cadherin/ Msx1 interaction in the development of a cohesive, integrated corneal endothelium and functional anterior segment.
Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2011.

Iontophoresis, the application of low-level electrical current to promote movement of a substance across a boundary, was investigated in conjunction with topically applied eye medicines with easy to determine effect times through noninvasive methods (dilation/reversal, and intraocular pressure [IOP] lowering [glaucoma] medications) to assess their effect on tissues of the anterior segment of the eye Initial study focused on chemical stability of ophthalmic medications subjected to applied electrical currents. Twenty-four tested drugs (dilators, constrictors, IOP-reducing drugs, and anesthetics) underwent eleven iontophoretic treatment levels (10muA-20mA) for durations of two minutes. Macroscopic observations, pH level, HPLC profiles, and solution resistivity were noted. All tested drugs remained chemically stable in the current density range of interest (≤1.25mA/cm2); a subset of fourteen drugs displayed minimal changes through all currents Four of these drugs were used for subsequent in vivo testing in adult rabbits: phenylephrine hydrochloride, pilocarpine hydrochloride, timolol hemihydrate, and brimonidine tartrate. Three iontophoretic treatment conditions were investigated for dilation/reversal (0.5mA for 60sec, 1mA for 30sec, and 1mA for 60sec), and one treatment condition for IOP lowering drugs (1mA for 60sec), lontophoretic current was delivered via a TENS electrode atop a closed eyelid after one drop of drug was administered topically to the eye. No significant difference was observed between iontophoretically treated and untreated eyes in time-to-effect for dilation using phenylephrine hydrochloride (p=0.22, n=8) or reversal using pilocarpine hydrochloride (p=0.32, n=8), or for maximum obtained pupil size (p=0.51, n=8). A significant reduction in time-to-effect was observed iontophoretically for the IOP lowering medication timolol hemihydrate (p=0.05, n=2), but not for brimonidine tartrate (p=0.15, n=3) The in vitro iontophoretic method employed in this study successfully verified chemical stability after current application for 14 of the 24 tested drugs, of which 4 drugs were subsequently tested for iontophoretic use in vivo. The particular in vivo iontophoretic method employed in this study, while designed around constraints of patient acceptance associated with eventual deployment to human clinical use, was unsuccessful at achieving efficiency that would justify further development. Future refinements to the in vivo method may alter this assessment
acase@tulane.edu

No
PURPOSE. The Activities of Daily Vision Scale (ADVS) has been extensively validated by traditional methodology. In the current study, Rasch analysis was used to explore further the validity of the ADVS and to determine whether improvements could be made. METHODS. Forty-three patients with cataract underwent visual acuity (VA) and contrast sensitivity (CS) testing and completed the ADVS. The data were Rasch analyzed and the value of response scale and item reduction explored. A shortened version and the original ADVS were tested for criterion validity by determining correlations with VA and CS. RESULTS. The ADVS data contained nonnormally distributed items and items with ceiling effects and empty response categories. Therefore, items benefited from shortening the response scale, the optimum length being three responses. There was poor targeting of item difficulty to patient ability, because many patients with cataract were sufficiently able that they had no difficulty with many activities. Items were eliminated if the task was too easy or did not fit with the overall concept of visual disability determined by the Rasch model. A reduced ADVS version was established that had adequate precision, equivalent criterion validity, and improved targeting of item difficulty to patient ability, but this version was still not ideal. CONCLUSIONS. Despite careful traditional validation, the ADVS data contained inadequacies exposed by Rasch analysis. Through Rasch scaling, particularly with response scale reduction, the ADVS can be improved, but additional questions seem to be needed to suit the more able, including patients undergoing second eye cataract surgery. There remains a need to develop Rasch-scaled measures of visual disability for use in ophthalmic outcomes research.

Aim: To assess the ability of critical flicker frequency (CFF) and optimal reading speed (ORS) to predict the potential vision in patients with cataract with and without ocular comorbidity. Methods: The two novel tests were compared with two well established potential vision tests (PVTs), the potential acuity meter (PAM) and the laser interferometer (LI). Measurements were made preoperatively in 1 eye of 88 subjects using the battery of 4 PVTs. Postoperative measurements were made with the CFF and the ORS. The subjects studied were consecutive cases over a 12-month period who fulfilled the inclusion and exclusion criteria, and agreed to participate in this study. Results: CFF was the PVT most resistant to the presence of cataract. Both CFF and ORS give a similar predictive precision in the presence of cataract and ocular comorbidity, although CFF seems more precise when the cataract is dense. Conclusions: The PAM and the LI showed a limited clinical capability in predicting postoperative visual acuity, particularly with dense opacities. The CFF shows the most promise as a PVT, particularly with dense cataract. Further evaluation is required for both CFF and ORS.