Thesis (Ph.D.)--Indiana University, School of Optometry, 2009. / Title from PDF t.p. (viewed on Jul 20, 2010). Source: Dissertation Abstracts International, Volume: 70-12, Section: B, page: 7503. Adviser: Stephen A. Burns.

Thesis (Ph.D.)--Indiana University, School of Optometry, 2009. / Title from PDF t.p. (viewed on Jul 22, 2010). Source: Dissertation Abstracts International, Volume: 70-12, Section: B, page: 7504. Adviser: Sangly P. Srinivas.

Thesis (M.P.H.)--University of Hong Kong, 2005.

Thesis--Universität Erlangen-Nürnberg. / At head of title: Aus dem Seminar für Geschichte der Medizin der Universität Erlangen-Nürnberg. Vita. Includes index.

<p>The complex process of visually interpreting our environment begins with the task of detecting the light that enters our eyes. This task is performed by the rod and cone photoreceptors, which both contain a highly evolved sensory cilium called the outer segment. The outer segment is a specialized cellular compartment that contains all of the protein machinery involved in converting the initial light signal into an electrical signal that can be ultimately transmitted to the brain. Outer segments are cylindrical structures that envelop an array of individual, densely packed membrane discs. Discs are renewed throughout the lifetime of a photoreceptor, with older material being shed at the tip and new material added at the base of the outer segment. Many studies conducted over the past 35 years conclude that disc formation starts with evagination of the plasma membrane at the outer segment base, followed by membrane expansion and, in the case of rods, subsequent disc enclosure. Despite the intense interest in the topic, the molecular mechanisms governing how outer segment discs are formed and renewed are not well understood. </p><p>The focus of this dissertation centers on elucidating the molecular role of peripherin/retinal degeneration slow (rds) in outer segment disc morphogenesis, including study of peripherin/rds trafficking from its site of synthesis in the endoplasmic reticulum to its site of function in the outer segment. Peripherin/rds is expressed specifically in photoreceptor outer segments, where it fulfills a critical role in assembling and/or maintaining the structure of this organelle. Mutation or loss of peripherin/rds in humans is often associated with visual impairments, and its knockout in mice results in rudimentary ciliary stumps completely lacking disc structures. </p><p>We found that early outer segment morphogenesis steps in mice lacking peripherin/RDS proceed normally for the first week. However, in the second week of postnatal development at the onset of disc formation, mice lacking peripherin/RDS produce extracellular vesicles next to their connecting cilia rather than discs. We characterized these vesicles and determined that they are enriched in outer segment proteins, are ~230 nm in size, and are formed as outward buds of the plasma membrane. These characteristics allowed us to classify these extracellular vesicles as ciliary ectosomes. Furthermore, we determined that ectosome shedding is arrested upon expression of the peripherin/rds C-terminal cytoplasmic sequence, which allows for the accumulation of excessive membranous material. Thus, we conclude that peripherin/rds transforms the functional dynamics of photoreceptor primary cilium from shedding massive amounts of ectosomes to retaining these membranes in the outer segment to eventually become photoreceptor discs. This novel function of peripherin is performed by its C-terminal cytoplasmic sequence and represents the first step in disc morphogenesis. </p><p>Finally, the morphogenesis study of peripherin/rds is complemented by a study of its trafficking. Understanding how peripherin is delivered from the site of its synthesis is critical for its function at the outer segment. We show that the peripherin/rds targeting sequence is confined within ten amino acid residues, which do not overlap with the putative fusogenic domain, and that only a single amino acid within this region is irreplaceable, a highly conserved valine at position 332.</p><p>Collectively, these studies shed considerable light on the molecular role played by peripherin. Peripherin is a photoreceptor specific protein that transforms the primary sensory cilium into a specialized sensory cilium capable of building the discs required for efficient photon capture. While work in this direction provides a significant advance in our understanding of peripherin’s role in disc morphogenesis, questions such as whether peripherin participates in disc enclosure, remain to be solved.</p> / Dissertation

This thesis describes the developm ent o f Dynamic Noise Perimetry (DNP), a novel method based on the equivalent noise input technique. The method, specifically targeted to an early stage o f OAG, used a 0.5 cycle per degree sine-wave grating presented at 8Hz in conjunction with an external noise m ask that was optimised for the stimulus. Equivalent noise and sampling efficiency w ere determ ined at various locations within the visual field to identify a stage o f the disease that was analogous to ganglion cell shrinkage, a stage which is believed to precede conventional methods o f detection. A pilot study initially determ ined w hether the spatial parameters o f the mask, in terms o f noise check size, were dependent on the spatial and temporal param eters o f the grating stimulus. The results show ed that the m axim al dimensions o f each check, i.e. the critical check size, were correlated w ith the drift frequency o f the stimulus. In a second and preliminary study, the variation in the critical check size with grating spatial and temporal frequency was investigated as a function o f eccentricity. Critical noise check size, in terms o f noise checks per cycle, decreased w ith increasing spatial frequency and drift frequency o f the stimulus, and with eccentric viewing. These results were used to optim ise the critical parameters for the noise mask. Temporal contrast sensitivity, equivalent noise and sampling efficiency were determined at various locations in the visual field, in 20 normal individuals and in 10 individuals with OAG. Temporal contrast sensitivity was reduced, and equivalent noise levels were elevated in early OAG, w hen com pared with normal individuals. Derivative measures o f sampling efficiency and equivalent noise declined with glaucomatous field loss. DNP was able to identify individuals w ith OAG, at locations which exhibited abnormal Pattern Deviation values and/ or abnorm al retinal nerve fibre layer thickness. DNP clearly warrants further development

The optical and biomechanical properties of the cornea are largely governed by the collagen-rich stroma, a layer that represents approximately 90% of the total thickness. It has been postulated that a novel corneal layer exists in the posterior stroma, immediately above Descemet’s membrane, termed ‘pre-Descemet’s layer’. The main aim of this thesis was to determine if this region has different structural properties to the overlying stroma. A second aim was to examine the elastic fibre distribution throughout the depth of the stroma in healthy and diseased corneas, with focus on pre-Descemet’s layer. Techniques used include serial block face scanning electron microscopy, transmission electron microscopy, and X-ray diffraction, amongst various other imaging techniques. Depth analysis revealed that centre-to-centre interfibrillar spacing was significantly lower in the first ~10µm of stroma distal to Descemet’s membrane compared to overlying regions in central cornea. Three-dimensional analysis revealed the presence of long elastic fibres running throughout the stroma, parallel to the surface of the cornea, which were concentrated in pre-Descemet’s layer. This elastic material seemed to originate from the limbus as fenestrated sheets before travelling radially into the cornea as small fibres. This data provides evidence for pre-Descemet’s layer containing altered biomechanical properties that may contribute to the formation of a variable cleavage plane observed during pneumodissection. Additionally, the elastic fibre network is likely to play an important role in the deformation and recovery of the cornea. Furthermore, the presence of elastic fibres in foetal cornea suggests a potential role in development. The distribution of elastic fibres was very different in keratoconic buttons. No fibres were located above Descemet’s membrane, whereas the elastic fibres appeared concentrated below the epithelium in thinned coned regions, potentially as a biomechanical response to prevent rupture. Attempts were made to elucidate a functional role for elastic fibres by studying the corneas from a mouse model for Marfan syndrome, where there was a ~50% reduction in elastic fibre quantity. These corneas were significantly thinner and flatter than wild types suggesting that elastic fibres play a role in maintaining the shape of the cornea. Overall, this thesis has characterised pre-Descemet’s layer, demonstrating that structural differences are present. It is likely that the network of elastic fibres described in this thesis play a multi-functional role in the cornea.

Age-related macular degeneration (AMD) is predicted to affect 196 million people by 2020 (Wong et al. 2014). To date there is no clear pathogenesis for the condition however, hypoxia has been implicated (Stefánsson et al. 2011). Currently, treatment is only available for neovascular AMD. To develop treatments targeted for early AMD a better understanding of the pathogenesis is required. There is also a need for sensitive functional biomarkers to improve diagnosis and monitoring and to expedite the evaluation of therauptics in clinical trials. The aim of this research was to investigate the hypothesis that hypoxia is involved in the pathogenesis of early AMD. Studies were carried out exploring the effect of transient systemic hypoxia (14% oxygen) and hyperoxia (60% oxygen) on scotopic thresholds and electroretinograms (ERGs) of participants with early AMD. It was hypothesised that the visual function of participants with AMD, but not age-matched controls, would improve during the hyperoxic episode and that hypoxia would have a greater detrimental effect on visual function in people with early AMD. There were no significant differences in scotopic thresholds within each group when breathing 60% or 14% oxygen compared to medical air (21% oxygen). There were also no significant differences in full-field ERG parameters between gas conditions or groups, apart from the amplitude of the b-wave which was significantly reduced under hypoxia in the control group. The amplitude of the focal flicker ERG was significantly higher in the control group than the AMD group when breathing both 14% and 21% oxygen. However, there were no significant differences in the parameters of the focal ERG within each group. These findings suggest that hypoxia is not responsible for the elevation of scotopic thresholds reported in AMD. There is also no evidence that ERG changes are attributable to hypoxia. This thesis provides no evidence to support the role of hypoxia in the pathogenesis of early AMD.

Glaucoma is a leading cause of blindness. As a progressive condition, it is important to monitor how the visual field (VF) changes over time with perimetry in preventing vision from deteriorating to a stage where quality of life is affected. However, there is little evidence of how clinical measurements correlate with meaningful quality of life landmarks for the patient or, by extension, the proportion of patients in danger of progressing to these landmarks. Further, measurement variability associated with visual fields make it difficult to monitor true change over time. The purpose of this thesis was to use large-scale clinical data (almost 500,000 VFs) to address some of these issues. The first study attempted to relate clinical measurements of glaucoma severity to UK legal fitness to drive status. Legal fitness to drive (LFTD) was estimated using the integrated visual field as a surrogate of the Esterman test, which is the approved method by the UK DVLA of defining LFTD, while the mean deviation (MD) was used to represent defect severity. An MD of -14dB or worse in the better eye was found to be associated with a 92% (95% Confidence Interval [CI]: 87-95%) probability of being legally unfit to drive. The second study used a statistical model to estimate the number of patients progressing at rates that could lead to this landmark of significant visual impairment or blindness in their predicted remaining lifetime. A significant minority of patients were progressing at rates that could lead to statutory blindness, as defined by the US Social Security Administration, in their predicted remaining lifetime (5.2% [CI: 4.5-6.0%]) with a further 10% in danger of becoming legally unfit to drive (10.4% [CI: 9.4-11.4%]). More than 90% (CI: 85.7-94.3%) of patients predicted to progress to statutory blindness had an MD worse than -6dB in at least one eye at presentation, suggesting an association between baseline VF damage and risk of future impairment. The next section investigated whether choice of testing algorithm, SITA Standard or SITA Fast, affected the time taken to detect progression in VF follow-up. The precision of the tests was measured using linear modelling techniques and the impact of these differences was analysed using simulations. Though SITA Fast was found to be slightly less precise, no evidence was found to suggest that this resulted in progression being detected later. The final study evaluated a validated and published risk calculator, which utilised baseline risk factors to profile risk of fast progression. A simpler model using baseline VF data was developed to have similar statistical properties for comparison(including equivalent R2 statistics). The results suggested that risk calculators with low R2 statistics had little utility for predicting future progression rate in clinical practice. Together these results contribute a variety of novel findings and demonstrate the benefit of using large quantities of data collected from the everyday clinical milieu to extend clinical knowledge.

A retrospective chart review performed from January 2009 to October 2013 assessed 1009 cases that underwent LASEK treatment using 20% alcohol and 120 mm eye spatula for epithelium mobilization; the STAR S4 IR^TM Excimer Laser was used to treat the eye. Evaluation of intraoperative flap events was conducted to assess the efficacy behind this minimal technique posed by surgeon, Dr. Samir Melki. Out of 1009 cases, 72.35% operative eyes showed complete flap preservation, 17.65% flap tears, and 10.01% flaps discarded, demonstrating the viability in applying this technique. All patients considered were required to have a pre-operative consultation to identify any possibly risk factors before surgery. For the purposes of this study, we investigated if age played a significant role in the intraoperative success of mechanically mobilizing the epithelium after 40-second alcohol exposure. We found that patients 50 years and older were statistically different from their younger counterparts (e.g. 20 to 29, 30 to 39, 40 to 49). They were more at risk for less epithelial preservation (e.g. flap equal to or less than 180 degrees) and overall flap removal (p < 0.001). There were no statistically significant differences between the age group 20 to 29 and 30 to 39; however, there was a relatively significant disparity in successful flap events for patients in their 20s versus those in their 40s (p < 0.001) suggesting that as one ages, the likelihood of flap tear increases.