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.

Age-related macular degeneration (AMD) is a major cause of irreversible central sight loss in the elderly. Many factors affect disease onset and progression, and these include age, environmental stressors such as smoking, diet, inflammation and genetic polymorphisms, all of which are likely to influence metabolism. In some complex diseases, metabolomics, which involves the identification of a metabolic fingerprint in a biofluid or tissue, has been shown to discriminate metabolic changes associated with different disease processes and to identify specific phenotypes. We have applied metabolomics, in the first study of its kind, to analyse, using NMR spectroscopy, both serum and urine metabolic characteristics in patients with dry and wet AMD (n=104). NMR spectral analysis showed good clustering as well as separation among the serum and urine from dry and wet AMD patients. The results show that metabolite profiles can distinguish dry and wet AMD, but that the pathways involved, glycolysis, urea cycle and Kreb’s cycle, are involved in both forms of the disease. It is likely that the pathogenesis of dry and wet AMD is similar and that the severity of ocular damage and systemic inflammation would account for the distinguishing profiles. These data support the use of metabolomics in identifying biological pathways involved in pathogenesis of AMD, but not in the diagnosis or prognosis of disease.

Age-related macular degeneration (AMD) is of increasing concern given the ageing population, and the associated economic and social burdens. Vision-related quality-of-life (QoL) is arguably one of the most important factors in the management of those with AMD. Consequently, there is a clear need for an understanding of the clinical outcomes that influence vision-related QoL in order to inform management strategies. The principle aim of the studies described herein was to determine the factors that predict vision-related QoL in those with AMD, over 1 year. Experimental procedures were undertaken at baseline (n=52 individuals with AMD) and repeated after 1 year (n=32 individuals with AMD). These included: visual acuity, contrast sensitivity, reading speed, microperimetry, optical coherence tomography and fundus photography. A questionnaire interview included assessment of vision-related QoL (Impact of Visual Impairment questionnaire), health status (EQ-5D), level of depressive symptoms (PHQ-9) and well-being (Warwick-Edinburgh Well-Being Scale). At baseline, the optimum multiple regression model accounted for 41% of the variance in vision-related QoL and included Mean Total Deviation or Mean Sensitivity with level of depressive symptoms. After 1 year, the optimum model to predict change in vision-related QoL accounted for 43% of the variance and included baseline contrast sensitivity and change in health status and reading speed. The most clinically useful measures of visual function, in identifying those with a reduced QoL or those at risk of a reduced QoL were contrast sensitivity, microperimetry, and reading speed. These outcomes may allow a better understanding of vision-related QoL if they were adopted in a clinical setting. In conclusion, the studies provide sufficient evidence to encourage a review of the clinical outcome measures most relevant to vision-related QoL.

Macular telangiectasia type 2, or MacTel, is an adult onset retinal disease that causes progressive loss of central vision, usually beginning between the 5th and 7th decades of life. Macular degenerative diseases comprise a large portion of the blinding diseases affecting people over the age of 50. The collective burden of vision loss and low vision includes the impact on patients in loss of independence and decline of self-reported quality of life, as well as significant resource allocation in medical and supportive care. There are no cures for macular diseases; currently available treatments may slow the progression in some cases, but patients remain at risk of losing their eyesight and the independence that vision affords. While macular telangiectasia is not as prevalent as other macular degenerative diseases, such as age-related macular degeneration, elucidating the causes of MacTel may reveal mechanisms that are common to other macular diseases, providing clues to guide research into possible treatment targets. In this work, I have assembled the first cohort of MacTel patients and their family members in collaboration with the MacTel Project, an international consortium of researchers and clinicians dedicated to studying this disease. I have identified and analyzed families with multiple affected relatives in which MacTel appears to be an inherited disease. The goal of this work has been to identify a genetic cause for the disease in these families. To that end, I used genotyping data from approximately 900,000 single nucleotide polymorphism per individual to create sets of genetic markers for linkage analysis. I analyzed these markers using two-point and multipoint linkage algorithms to search for a region of the genome that was inherited in conjunction with the phenotype more often than would be expected by chance alone, with the goal of finding a causative genetic variant. This analysis resulted in the identification of a region of chromosome 1 spanning approximately 15 million bases that is significantly linked to the MacTel phenotype. I analyzed recombination breakpoints in this region, as well as across the genome, to map chromosomal segments inherited identical by descent in siblings that express the MacTel phenotype. This approach provided a profile for each set of siblings of regions of the genome incompatible with inherited genetic disease by virtue of the fact that no alleles were shared identical by descent. I then compared these regions across families under the hypothesis that if MacTel is caused by the same gene in all families, the chromosomal region harboring a causative variant would fail to be excluded in any family. This analysis excluded much of the genome and refined the boundaries of the linkage interval on chromosome 1, but did not appreciably narrow the region of interest. In parallel with analysis of linkage in families, I sequenced 40 genes of interest as possible functional candidates, using Sanger sequencing in the probands of families with multiple affected relatives. I selected candidate genes based on gene function and expression, choosing genes with a plausible connection to the phenotype based on information in the literature. Thirteen of these genes were selected based on their location in the region of the maximum linkage score. I was unable to identify any variant that was consistent with being a causative variant for inherited MacTel.

The studies comprising this thesis were conducted to examine the potential of a range of cross-linking therapies; in particular, to investigate the effect of a novel cross-linking therapy (involving a bacteriochlorophyll derivative and near-infra red illumination (WST-D/NIR)) on the structure of the cornea, and to develop a trans-epithelial riboflavin/Ultraviolet-A (UVA) corneal cross-linking protocol that was equally effective to that of the standard protocol (SCXL), without the need for epithelium removal. A number of laboratory techniques were used to investigate changes in the structure of the cornea and its biochemical and biomechanical properties following cross-linking. X-ray scattering and electron microscopy data provided evidence that treatment with WST-D/NIR resulted in no change in corneal collagen organisation and confirmed its potential as an alternative to riboflavin/UVA cross-linking for stiffening diseased or surgically weakened corneas. Enzyme digestion studies and strip extensometry were performed to compare the effectiveness of newly developed riboflavin/UVA protocols to that of the SCXL protocol in terms of their ability to increase the enzymatic resistance and stiffness of the cornea. The studies indicated that the intensity and distribution of cross-links formed within the cornea vary with different protocols, and that the outcome of trans-epithelial riboflavin/UVA cross-linking may be significantly enhanced through the use of higher concentrations of riboflavin, a longer duration of iontophoresis and the use of pulsed and higher energy dose UVA. Although the precise amount of CXL required to prevent the disease progression is still unidentified, the full stromal depth of CXL post SCXL treatment might not be needed, therefore, modified trans-epithelial protocols identified in this thesis may be sufficient to prevent disease progression. Further clinical studies, especially randomized prospective trials, are, however, required to confirm the encouraging results of these modified procedures.

A two-stage qualitative research strategy using semi-structured interviews was conducted with a convenience sample of 45 participants who lives with type 2 diabetes. In Stage One of the research, a qualitative study was conducted using semi-structured interviews with a purposive sample of 25 participants. Of these, 20 participants were diagnosed with type 2 diabetes, two participants were primary care physicians, two were ophthalmologists, and one was a retinal screener. People with diabetes were purposely recruited to fall into four groups with different grades of diabetic retinopathy. The aim of Stage One was to explore how people with type 2 diabetes perceive diabetic retinopathy risk, their understanding of risk information, and to appraise existing risk communication tools that have been used in other clinical settings. The data from Stage One was analysed and used to develop a risk communication tool designed to provide risk information about diabetic retinopathy and diabetic screening results to people with type 2 diabetes, which was then used in Stage Two. In Stage Two of this research, a total of twenty people with type 2 diabetes were recruited. Participants were divided into two groups based on their grade of diabetic retinopathy. Group one: 10 participants with no diabetic retinopathy (R0); Group two: 10 participants who had background diabetic retinopathy (R1). The aim of Stage Two was to i) appraise a newly developed risk communication tool that was developed to communicate risk information about diabetic retinopathy to people with type 2 diabetes, ii) to explore the influence of the new developed risk tool on risk perception and on diabetes self-care management, and iii) to establish a method(s) by which risk information about diabetic retinopathy can be effectively communicated to people with type 2 diabetes. All interviews were audio recorded and transcribed using a digital recording machine. Data was analysed using constructivist grounded theory approach.

Movement has an effect upon the perceived spatial position of moving objects, such that they are not perceived at their instantaneous spatial position. Vision scientists named this phenomenon motion-induced position shift (MIPS). The reason, neural loci, and the mechanisms causing the positional illusion have challenged scientists over the last century. Nowadays, many vehicles, such as cars, planes and submarines are equipped with onboard computers containing touchscreens. Active controls of those on-board computers require visuomotor-actions, which could be affected by perceptual illusions, but also require time, and attention. Hence, it is becoming more crucial to fully understand how the visual system generates visuomotor-guided actions, and how it copes with visual illusions. Human-machine interactions could be designed such that perceptual illusions would be 1) avoided, or 2) predicted, and considered in human actions, or such that 3) the user interacted with visuomotor actions that resisted visual illusions. One alternative to finger points towards on-board computers is saccadic eye movements. The saccadic system is very fast, and therefore, would not require as much time and attention as a finger point task towards the touch screen. Saccades are constantly facing the challenge of localising objects, which makes it interesting to study how they cope with visual illusions like the motion-induced position shift. The purpose of this thesis was to establish if the saccadic system was affected by the motion-induced position shift in the same manner as the perceptual system was affected. I confirmed that movement had an effect upon the perceived spatial position of moving objects in perception-tasks and in volitional saccades. A previous study showed that reflexive saccades resisted the illusion, indicating that they were more accurate than other visually guided actions. I replicated these results, but claimed that the results are not representative. As a consequence, there is no evidence that reflexive saccades do escape the visual illusion while volitional saccades do not.

The aim of this study was to investigate differential aspects of spatial vision in subjects presenting with macular degeneration and visual snow. Emphasis was placed on the effects of aging and/or ocular disease on binocular summation and the measurement of differences between the two eyes in a number of visual tasks. Accommodation performance was measured for both pre-presbyopic and presbyopic observers. The results showed no binocular advantage for either group for far or intermediate stimulus vergences. The effects of visual crowding upon visual acuity were tested using a Landolt C optotype with surrounding distractors. Binocular advantage was found to be higher along the line of sight and to decrease in the near periphery. The presence of distractors reduced visual resolution significantly at every eccentricity, with the effect becoming more pronounced in the periphery. The latter was observed for both monocular and binocular viewing conditions leading to the suggestion that the involvement of binocularly driven neurons may not be essential for visual crowding. The effects of healthy aging and ocular disease on spatial and chromatic vision were also investigated. It was found that stimulus presentation time in a gap acuity task affects visual acuity differently in patients with Age-related Macular Degeneration (AMD) when compared to normal subjects. The processing of briefly presented optotypes appears to be severely reduced in AMD patients. Visual performance was also investigated in patients who experience ‘visual snow’. While gap acuity at any stimulus duration and the strength of chromatic afterimages were found to be unaffected, involuntary pupil recovery following brief exposure to chromatic stimuli was found to be delayed in 3 of the 6 visual snow (VS) patients examined. The absence of a normal pupil recovery is consistent with abnormally slow signals that may also play a part in VS. The novel findings reported in this thesis suggest that advanced vision tests can be used to quantify the effects of normal aging and to detect and monitor the earliest changes in diseases of the eye.

There is little epidemiological information about cataract in children globally and thus a lack of evidence to guide policy related to childhood cataract. Early presentation for cataract surgery in children is an important first step for effective treatment. The overall aim of this research was to determine the age at childhood cataract surgery in India and to understand the barriers and enablers to accessing childhood cataract services in the region. A mixed methods approach was used. Quantitative data were obtained via a questionnaire in nine different eye hospitals in eight states in India. Qualitative data were collected from the perspectives of parents and carers and primary eye care providers using in-depth interviews and focus group discussions respectively and Theoretical Domains Framework (TDF) of behaviour change was used for analysis. A systematic review was conducted to estimate global prevalence of childhood cataract. This was estimated to be 1.14 /10000 overall, and 0.46 /10000 in low and lower middle income economies. The mean age at surgery for congenital cataract in India was 4 years and for developmental cataract it was 8 years, but these numbers varied significantly between the regions in the country. Delays to surgery occurred at recognition, when accessing the hospital and delayed surgery at the hospital. The barriers and enablers identified from the perspectives of the parents and carers suggest a need for behavioural change intervention to enhance health seeking behaviour in the communities. The findings suggest gaps in knowledge and awareness among the primary care team which should be further investigated and addressed. Based on these research findings several recommendations were identified and a preliminary recommended intervention strategy was developed to achieve behaviour changes with the aim of increasing early uptake of childhood cataract services in India.

Refractive errors such as myopia are the leading cause of reversible visual impairment worldwide with their prevalence rapidly increasing, resulting in greater burden on public health services. The aim of this series of investigations was to leverage the latest statistical methods and large-scale cohorts available in order to develop our understanding of the genetic determinants for the refractive error traits of spherical equivalent, corneal astigmatism and refractive astigmatism. Investigation of genetic variants on the X-chromosome, a region often neglected in genome-wide association studies (GWAS), identified four genes demonstrating association in a gene-based analysis of spherical equivalent for a cohort of teenagers. Meta-analysis of GWAS results for corneal astigmatism including European and Asian ancestry cohorts performed on behalf of the CREAM consortium successfully replicated the previously identified association near the PDGFRA gene (lead variant: rs7673984, odds ratio = 1.12, P = 5.55 × 10−9). The availability of data from the UK Biobank facilitated the largest GWAS for corneal and refractive astigmatism performed to date (N = 86,335 and 88,005 respectively). Here, GWAS for these traits identified four and two novel loci associated with corneal and refractive astigmatism respectively. Each of these loci had previously been associated with other ocular traits including myopia. Phenotypic variance explained by common genetic variants was relatively low for corneal and refractive astigmatism at ~6% and ~5% respectively, thus proposing a greater role for rare variants in explaining astigmatism variance due to genetics. Lastly, in order to link identified variants and genes functionally influenced in myopia development, several candidate myopia genes identified from a primate myopia model demonstrated enrichment with refractive error associated variants in human samples. Overall, the findings from these investigations are a starting point in guiding further research into the complex biological mechanisms underlying refractive error development.