The study describes the morphology of eyes in children and adults with Down's syndrome (DS) including ocular biometric parameters (axial length, cornea, anterior chamber, lens and pupil size) and retinal features. There was no significant difference in the correlation of axial length and refraction between DS children (n=46) and controls (n=50). Children with DS (n=18) and adults with DS (n=10) have significantly thinner corneas both in the centre and periphery, smaller corneal radius, higher corneal power, higher corneal aberration and lower lens power compared to their respective control children (n=28) and adults (n=16). Further, in spite of abnormal ocular parameters, refraction in people with DS appeared to be determined by a similar correlation between those parameters as in controls. A larger disc and rim were found in children with DS (n=17) compared to controls (n=28). An increased number of vessels were found in periphery of the retina in children with DS. However, there was a similar distribution of retinal vessels in DS children (n=31) and controls (n=40). The presence of the peripapillary atrophy in children (67%) was much higher than that of controls (28%). No significant correlation was found between the total number of vessels and visual function such as refraction, visual acuity and accommodation among children with DS. Keratoconus was present in 8 adults with DS, however, no keratoconus was found in children with DS but abnormal corneal topography was more common in children with DS compared to that in controls.

Laser <italic>in situ</italic> keratomileusis (LASIK) is a surgical technique used to correct refractive errors by reshaping the cornea. Although LASIK is superior to other visual correction techniques, recent clinical reports show that, in some cases, it leads to serious optical problems. Therefore, the aim of this thesis was to study the corneal ultrastructure in normal and LASIK corneas and discover a reason for the deterioration of vision in some LASIK patients. Different experiments were run, from experiments to improve understanding of the collagen fibril arrangement in the human cornea to studying the corneal changes in post-LASIK ectasia. Also, different techniques were used in this study including wide-angle x-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and light microscopy (LM). XRD showed that the human cornea possesses a unique orthogonal central collagen fibril orientation that was not found in the corneas of animals, such as camels or rabbits, which were found to have unidirectional or circular collagen orientation respectively. However, all human, camel, and rabbit corneas were found to have the same collagen fibril orientation around the limbus, that is, an annulus circumscribing the cornea. XRD was also used to study the effect of corneal full-thickness trephination on collagen fibril arrangement, trying to mimic penetrating keratoplasty (PKP) and LASIK procedures. The results indicate that central corneal trephination (at 4 mm diameter) will change the collagen fibril arrangement around the trephine-wound edges. This effect will be reduced if the trephination is made away from the centre, toward the limbus. These results may encourage ophthalmic surgeons to use a large graft diameter for PKP in order to avoid postoperative complications such as astigmatism. Also, these results may give a good explanation for the low post-LASIK astigmatism rate found in the literature. As LASIK surgery includes flap creation and laser ablation, it was preferable to study the collagen fibril arrangement at different corneal depths (by means of femtosecond laser and XRD) in order to understand the precise effect of the LASIK technique on collagen lamellae. It was found that the first third (33%) of the corneal thickness has an irregular collagen lamellar orientation whereas the orientation clearly becomes orthogonal towards the posterior cornea (endothelium side). Thus, it can be concluded that LASIK flap creation and laser stromal ablation usually occur in the irregular collagen fibril layers. These layers have been found to be the strongest part of the cornea and are essential to maintain corneal curvature and strength. Therefore, these findings allow us to understand the reason for high astigmatism or ectasia in some LASIK patients. <italic>In vitro</italic> LASIK was then conducted on donor human corneas to simulate the <italic>in vivo</italic> situation of LASIK so that the collagen fibril orientation and other corneal structural changes could be studied by means of XRD, SEM, and TEM. XRD results indicated that the collagen fibril orientation and distribution after LASIK are similar to those in normal corneas. This normal orientation was expected because the flap creation and the laser ablation usually occurred in the first third of the corneal thickness, which has been found to have an irregular collagen fibril orientation and hence, the full corneal thickness XRD cannot reveal the localised effects of LASIK. XRD on post-LASIK ectatic corneas showed that the collagen fibril orientation was also similar to that of the normal cornea, that is, it showed an orthogonal collagen orientation. TEM, SEM, and LM of normal and ectatic LASIK corneas showed that the flap-bed interface can be detected easily regardless of the time after surgery flap borders have been detected up to 10 years after the LASIK procedure. Moreover, the results indicate that the LASIK corneal wound healing happens superficially (epithelium healing only) and also show that the collagen lamellae do not bond with each other again after LASIK, which leaves the flap weak and, thus, explains the easy separation or dislocation of the flap from the stromal bed months or years after surgery. Also, the results give an overview of the corneal biomechanical insults caused by the LASIK flap, which seem difficult to avoid and, in some cases, may lead to ectasia. Interestingly, TEM shows that the collagen fibril diameter and interfibrillar spacing of both normal and ectatic LASIK corneas appear similar to those in normal corneas, which may explain the perfect visual acuity results obtained immediately after LASIK surgery and, also, indicates (according to the above results) that the reduced vision in ectatic patients is not a result of any disarrangement of the collagen fibrils, which is known to affect corneal transparency, but, instead, is a result of a corneal biomechanics insult due to the flap creation and tissue ablation.

During development of the lens, epithelial cells at the lens equator begin a differentiation process to become secondary fibre cells. The differentiating cells elongate and migrate towards the centre of the lens where they envelop the older, central fibre cells. Differentiation into fibre cells is accompanied by the breakdown of all organelles, such as the mitochondria. All organelle degradation is completed and denucleation occurs at the border of the organelle free zone (OFZ) which contains the central, terminally differentiated, fibre cells. The differentiation pathway is not well characterised, though it is believed to have similarities to an attenuated form of apoptosis supported by the identification of apoptosis related genes, such as TNF, in the lens. This study continues the search for and characterisation of apoptosis related genes expressed during lens development, focusing on TNFs and their extended family. Reverse Transcriptase-(RT-) PCR was carried out, identifying a number of TNF and extended family member genes in the chick lens, expression studies established novel, statistically significant differential expression for TRAF2 and TRAF3. TRAF2 protein expression from western blotting, similar to RT-PCR expression was found to decline as the lens developed. TRAF2 localisation studies showed limited expression in the equatorial region but there was extensive signalling found in the developing iris, a region in the corneal-scleral boundary and some staining was also detected in the ciliary body. TRAF3 protein and RT-PCR expression were similar, with increasing expression as the lens developed. Western blotting identified two bands and subcellular fractionation confirmed different localisation for the two isoforms. Immunofluorescence identified increasing TRAF3 staining in the cortical fibre cells, this staining was found to be similar to proteins that were reported to be involved in lens fibre cell remodelling and maintenance, suggesting a possibly similar role for TRAF3. Following interest in TRAIL as a gene therapy for Posterior Capsule Opacification (PCO) its expression was examined using RT-PCR and Western blotting which showed low, similar levels of expression throughout the stages of lens development studied. Peroxidase staining showed interesting staining in the equatorial epithelial cells and those just beginning to differentiate at the transition zone. Novel nuclear staining was identified at all time points in both epithelial and fibre cells containing nuclei. Characterisation of whole lens culture was undertaken to discover the optimum culture system for the whole chick lens. Of the published research using whole chick lens culture none stated the basic morphology of the developing lens in organ culture, though each lab had their preferred methodology. The characterisation resulted in the preference of E10 chick lenses being grown with vitreous attached in medium containing glucose. Understanding the morphology of lenses in culture will be invaluable when undertaking the functional studies required to clarify the roles in the lens of the newly identified genes, specifically TRAF2 and TRAF3.

<bold>Chapter 6</bold> outlines an initial analysis of a database that was set up to enable clinical audit of the WLVS.&nbsp; The characteristics of those who used the service for the first time and how this changed as the service developed were investigated.

The cornea is a remarkable connective tissue that is transparent to visible light as a consequence of the regularly arranged, uniformly-sized collagen fibrils that constitute it. Evidence suggests that this intricate collagen fibril architecture is maintained by the presence of keratan sulphate-carrying proteoglycans (KSPGs) within the corneal stroma. The KSPGs, lumican, keratocan, and mimecan are believed to be involved in the regulation of collagen fibril diameter and fibril spacing. KSPGs have recently been investigated using transgenic technology, which allows the manipulation of gene expression in order to determine the significance of a gene product in a biological system. Thus, to ascertain the role of KSPGs in this thesis transgenic mice were used. Two methodologies were employed to investigate the structural organisation of collagen within normal and mutant mouse corneas small angle X-ray diffraction (XRD) provided quantitative information on collagen fibril spacing, collagen fibril diameter and degree of local order in the fibrillar array averaged throughout the tissue, and transmission electron microscopy (TEM) afforded a view of collagen fibril morphology within the tissue. Previous research has shown that a homozygous-null mutation for lumican affects corneal collagen fibril architecture. But no information exists about whether these structural changes develop in adulthood or start early in life. Thus, the role of lumican during neonatal corneal stromal development between days 8 and 14 was explored. Collagen fibril spacing is considerably higher in lumican-null corneas until day 14, and fibril diameter is, on average, smaller-than-normal. TEM provided evidence of stromal disorder in mutants and fibril fusion at day 14, indicating that lumican plays a key role in development of the neonate cornea. Next, the effect of a cysteine-serine substitution in the N-terminal region of lumican was investigated to determine the importance of this region in lumican-collagen interaction. Mutant collagen fibrils are appreciably larger in diameter, signifying failure of lumican to bind collagen and regulate fibril growth. This chapter also investigated the consequences of lumican over-expression, to reveal that excess lumican has no significant effect on mutant corneal stromal ultrastructure. The role of mimecan in the corneal ECM via ablation of gene expression was explored. The extent of ultrastructural alteration was minimal with mutants having collagen fibril spacing and fibril diameter that were essentially unchanged. This work indicated that mimecan plays a minor role in the maintenance of matrix structure in the cornea. Finally, to better understand what structural motifs contribute to KSPG effectivity, the significance of a carbohydrate sulphotransferase gene, ChstS, in the mouse corneal stroma was investigated. The ablation of ChstS, responsible for the production of a carbohydrate sulphotransferase enzyme, revealed that smaller fibril spacing and fibril diameters, and stromal disorganisation are the result. KSPGs are structurally and functionally distinctive. Mimecan appears to have little influence over matrix morphogenesis, and it is possible that absence of mimecan is compensated for by the upregulation of other PGs. In contrast, lumican is an important component of the ECM the structure of lumican bestows this molecule the ability to regulate matrix morphogenesis, as exemplified by absence of lumican and also N-terminal mutation of the core protein. Indeed, the sulphated form of KS is required within cornea, as the absence of a carbohydrate sulphotransferase gene renders the corneal stroma structurally altered.

The thesis investigated aspects of the perimetric threshold estimate with the aim of facilitating the outcome of the visual field examination. The difference in performance of the three current short-duration commercially available algorithms, SITA Standard, SITA Fast and TOP was investigated, relative to their respective 'gold standards' and to each other, in two separate studies of normal individuals and of patients with open angle glaucoma (OAG). The results for the normal individuals suggested that the TOP algorithm will overestimate the severity of the field loss relative to the Octopus Threshold and SITA Fast algorithms. However, for the patients with OAG, SITA Fast represented a good compromise between performance and examination duration. The inherent differences within- and between-algorithm for TOP suggests that an alternative should be utilised in clinical practice. The characteristics of the Frequency-of-seeing (FOS) curves for W-W perimetry and for SWAP were investigated for varying eccentricities in normal individuals and in patients with OAG. In the normal individuals, the slope of the FOS curve flattened and the magnitude of the 50th percentile decreased with increase in eccentricity for W-W perimetry and for SWAP. The magnitude of the slope was flatter at any given eccentricity for SWAP than for W-W perimetry. In patients with OAG, the magnitude of the slope was moderately correlated with the severity of field loss for W-W perimetry and for SWAP. The flatter slope of the FOS curve will always yield greater variability for SWAP than for W-W perimetry. The number of incorrect responses to the False-negative catch trials was investigated in patients with OAG as a function of the fatigue effect. No significant difference was found in the prevalence of incorrect responses with increase in fatigue. The prevalence of incorrect responses was modestly correlated with increasing severity of field loss. W-W perimetry, SWAP, SITA, TOP, FOS, False-negative catch trials.

Keratoconus is a non-inflammatory corneal disease that progressively causes topographical alteration of the cornea as a result of thinning, and consequently leads to impaired vision. In this thesis, the clinical studies are showed that the incidence rate and severity of keratoconus in Asir province, Saudi Arabia is high with an early onset and more rapid progress to the severe disease stage at a young age compared to other countries. The result also showed that the disease required different contact lens designs to be available in the clinics and the selection of initial back optic zone radius for multiple contact lens designs should be based in the steepest keratometric reading in early stage, and on average keratometric reading on moderate and advanced stages. However, regardless of the stage of disease, tricurve contact lens design should be selected based on average keratometric reading. Ultrastructure investigation of the anterior surface of Bowman's layer using different microscopes revealed that the changes are not limited to the apical cone only, but extend to the periphery of the cornea especially in the advances stage of keratoconus. Also, although the topographical map is usually used in trephination, it was found that the topographical features alone failed to indicate the full extent of the progress of keratoconus towards the corneal periphery. Data from transmission electron microscopy and high-angle X-ray diffraction suggest that the structural abnormalities in the stromal fibrillar matrix might be influential underlying reasons for topographic changes in the keratoconic-like changes of SPARC-null and JKC mice.

Adaptation to a high contrast grating temporarily reduces the contrast sensitivity of neurons in the primary visual cortex (VI). If this adaptation is induced in one eye and the contrast tested with the other a partial transfer of the after-effect is produced, known as interocular transfer (IOT). Intrinsic hyperpolarisation of a cells membrane explains most of this effect, but not the orientation selective nature of adaptation. Optical imaging of intrinsic signals in anaesthetised cats and tree shrews was used to visualise orientation selective responses in VI before and after brief and chronic adaptation. Short term adaptation was achieved with drifting gratings of 12.5 or 50% contrast and fixed orientation (0). Three 1-sec flashes of a 100% contrast grating were used as test stimuli. 8 orientation domains were created according to orientation preference, determined on the basis of pre-adaptation orientation maps. 8 oriented test stimulus responses for each domain were obtained from the absorption signal time course averaged over all pixels. Orientation tuning curves comparable to those in single-cell experiments were produced for the orientation selective pixel populations. A region specific reduction in response was seen in the tuning curves such that responses to 0 were reduced most strongly in regions responding best to 0. An additional stimulus specific reduction was observed in responses to 6, even if 0 wasn't the optimal orientation for a domain. Chronic adaptation was induced with 1 hour of drifting sinusoidal grating in tree shrews. In contrast to a similar experiment in the cat, no alteration in the functional layout of the orientation map was observed. Extracellular recording of IOT in the cat primary visual cortex was performed to elucidate its physiological substrate. Orientation tuning curves were recorded before and after left or right eye adaptation with a 25% or 50% contrast drifting grating with the cells preferred orientation and spatial frequency. Cells were <italic>a priori</italic> categorised according to the binocularity of their control responses. Surprisingly, significant levels of IOT were observed in virtually all monocular cells. Only a weak link was found between ocular dominance and IOT in the full cell population. However, a moderate link between OD and IOT was seen in simple cells. An increase in the response to orthogonal stimuli was also seen in both monocular and binocular cells after adaptation with the non-dominant eye. A subset of complex cells did not display any IOT when adapting with the non-dominant eye and testing with the dominant eye.

The arrangement of corneal collagen fibrils within lamellae was investigated by comparing fibril positions obtained from electron microscopy with distorted hexagonal, quasi-random and aperiodic arrays. By calculating the wavelength dependence and Fourier transforms of these various arrays it was determined that an aperiodic array based on the sunflower seed head is the most compatible with corneal ultrastructure. An investigation of corneal light scattering away from the central axis was undertaken for the first time. Experimentally it was shown that corneal transmission decreases peripherally, particularly in the far periphery near the limbus. This was shown to be theoretically compatible with calculated positional changes in refractive index and fibril radius, by calculating transmission using the direct summation of scattered fields method. In swollen human corneas, it was determined that there was a notable change in wavelength dependence in the peripheral regions, possibly suggesting an increase in the size and relative number fibril free voids. . Corneal infrared transmission is poorly studied. In this part of the spectrum, the cornea acts as an absorber of incident radiation. It was hypothesised that there should be a systematic variation between corneal hydration and infrared light transmission. Experimentally, by Fourier transform infrared spectroscopy a convenient linear relationship between hydration and transmission was found. Riboflavin-UVA crosslinking is used to treat keratoconus, a degenerative corneal disorder. A swelling experiment was performed on porcine corneas in order to elucidate whether the crosslinking mechanism is intra- or inter-fibrillar. Swelling rates for the treated and untreated tissue were not statistically significant, excluding interfibrillar crosslinking. The penetration depth of the riboflavin molecule into corneal stroma was also examined by visible spectroscopy of thin segments of tissue. It was demonstrated that when riboflavin infiltrates a full thickness cornea, the highest concentration of riboflavin is present in the anterior tissue segment.

CONCLUSION These data suggest a role for both angiogenic factors and anti-angiogenic factors and the caveolins in the pathogenesis of diabetic retinopathy, possibly by acting synergistically to mediate a wide range of cellular responses culminating in the formation of a fibrovascular membrane. Therapeutic intervention to the VEGF and Tie-2 receptor, and possibly stimulation of the PEDF signalling, pathways may prove useful for the treatment of PDR.