Age-related macular degeneration (AMD) is a leading cause of visual impairment and blindness, affecting over 30 million people worldwide. It is characterized by the appearance of insoluble deposits known as drusen in the outer retina, between the retinal pigment epithelium (RPE) and Bruch's membrane. Drusen are heterogeneously composed of many compounds, including cholesterol, amyloid-β, and complement proteins. AMD also involves the accumulation of pigments collectively termed lipofuscin in RPE lysosomes. The underlying causes of AMD are unknown, but studies have implicated inflammatory processes in its pathogenesis.

Sexual selection and the maintenance of species diversity in Lake Malawi cichlid fishes are greatly dependent on optical communication, which is influenced by environmental, physiological and endocrinological factors. The diversity in spectral sensitivity of cichlids has been partially attributed to differences in opsin gene expression, with each species preferentially expressing a subset of seven possible genes. Hormones such as gonadotropin releasing hormone (GnRH) can mediate changes in gene expression and the presence of GnRH immunoreactive fibers and GnRH receptors throughout the retinal layers make it an excellent candidate for mediating changes in visual processes. Effects of exogenous GnRH administration on the visual system of zebra cichlids (Metriaclima zebra) via prolonged release cholesterol implants and intubation was investigated using electroretinogram (ERG) recordings, quantitative real-time RT-PCR and in situ hybridization. Three week and ten week sampling periods were used in the intubation study. No obvious differences in spectral sensitivity were evident when looking at a-wave, b-wave and d-wave components of the ERG waveform in any of the treatment groups. A multiple mechanism model was used to describe the cone mechanisms mediating spectral sensitivity and this analysis showed that the activity of cones was shaped by opponent and non opponent cone interactions based on subsets of five opsin genes previously described in cichlids (SWS1, SWS2b, RH2b, RH2aβ, and RH2aα). Although differences in the spectral sensitivity between control and GnRH-treated fish were not evident on a functional level, there were changes in the gonadosomatic index in the intubation group. Quantitative real-time RT-PCR (qRT-PCR) and in situ hybridization demonstrated that treatment with a synthetic GnRH3 analogue using the oral intubation delivery system resulted in statistically significant changes in opsin gene expression in both three week and ten week treatment groups, specifically the upregulation of RH2b and the downregulation of RH2a opsin genes. Moreover, in situ hybridization analysis showed that the pattern of labeling for the RH2a and RH2b riboprobes corroborated the changes in opsin gene expression found in the qRT-PCR data. In contrast, GnRH treatment using the cholesterol implant delivery system did not result in significant changes in spectral sensitivity or opsin gene expression. / Thesis (Master, Biology) -- Queen's University, 2011-01-05 22:57:11.308

Carotenoids are essential for visual function, however their potential role in Computer Vision Syndrome (CVS) is not known. By providing carrot powder, this study examined carotenoid metabolism and visual function in CVS. CVS participants were recruited into a double-blind, placebo-controlled, repeated measures trial (n=19, ages 20-65) and were randomized to 2 supplementation groups; control (15g cream of wheat powder) or carrot enriched (15g carrot powder, 33% of vitamin A RDA for adults) in an isocaloric pudding and yogurt for 4 weeks. Retinal function, self-perceived vision status, and plasma carotenoids/retinoids were assessed, along with plasma lipids and oxidative stress markers. Photopic b-waves marginally improved following supplementation reflecting higher phototransduction, possibly due to increased plasma carotenoid/retinoid levels. LDL cholesterol and oxidative stress markers showed trending reductions illustrating a protective role of the carrot. Carrot powder, at a minimal supplementation dose, can be recommended for CVS.

Understanding how animals detect and discriminate different qualities of light is a key component of the study of visual ecology. My research investigated the use of three electrophysiological methods to assess the neuronal mechanisms involved in spectral and polarization sensitivity in one species of salmonid, the rainbow trout (Onchorynchus mykiss). 1 examined the neuronal mechanisms underlying polarization sensitivity using electroretinograms (ERG) and optic nerve compound action potential (CAP) recordings. Chromatic adaptation and pharmacological techniques were used to reveal opponent interaction at the cone-horizontal cell level and to provide the first evidence of retinal processing of polarization sensitivity. To facilitate additional research more suited to the exploration of neural networks and signaling, I developed the protocols and techniques necessary to investigate the spectral sensitivity of rainbow trout using whole-cell patch clamp (WPC) electrophysiology, and produced the first assessment of the ultraviolet component of spectral sensitivity in a vertebrate using this technique.

No description available.

In this study, fluorescein angiograms of the ocular fundus have been digitised to enable them to be processed and analysed by computer. A fully automated technique for counting microaneurysms (MA) in these images was developed with a view to producing an objective, accurate and highly repeatable way of quantifying these lesions. Prior to any other image processing, a number of pre-processing stages were applied in order to compensate for non-uniformaties and to remove the background fluorescence component present in all the images. Matched filters modelled on two-dimensional Gaussian distributions were employed to detect MA in the 'shade-corrected' images. A binary image representation of the vascular network was constructed. This 'vessel mask', used in conjunction with the original match-filtered images, enabled MA to be detected by grey-level thresholding the filtered images. The resulting binary objects could then be counted by the computer as MA. The automated technique was assessed by comparing the computer's results for six fluorescein angiograms with MA counts obtained by ophthalmologists analysing both analogue and digital images. The performance of both man and machine were judged with respect to 'gold standards' compiled from prints of the original negatives. The best results were obtained by the clinicians analysing the analogue prints, although they differed greatly in their ability to detect microaneurysms. The computer performed better than the clinicians when they were counting MA in the digital images and produced highly repeatable results. To improve the performance of the automated technique, images were captured at approximately four times the previous spatial resolution and a smaller area of each image was analysed. Additionally, more complex image-processing techniques were employed to increase the accuracy of the computer analysis. Although the performance of the automated technique was improved, the computer results only matched those of the clinicians' analogue analyses for two of the images.

Doctor of Philosophy (PhD) / Background: The development of the blood supply in the primate retina has been extensively studied; however the relationship of the differentiating retina to the choroidal blood supply is less well known. The interaction of astrocytes and vascular endothelial cells promotes the development of the retinal vasculature from 14 weeks’ gestation (WG). Initially, astrocytes lead the developing capillaries from the optic nerve towards the macular area. However, neither astrocytes nor endothelial cells enter a prescribed avascular area, within which the fovea later forms. This may be attributed to expression of a factor that inhibits astrocyte and endothelial cell proliferation in the fovea. A factor found in the CNS that is already known to have these effects is transforming growth factor-β (TGF-β). Aims: This thesis investigated the relationship between retinal maturation and choroidal blood vessel supply and the possible role for TGF-β as an antiangiogenic factor in maintaining an avascular fovea during primate retinal development. Methods: Human eyes between 11 WG and 40 years were obtained with ethical approval from Prince of Wales Hospital and the NSW Lions Eye Bank and fixed and sectioned for histological procedures or prepared for polymerase chain reaction (PCR). Macaque eyes from foetal day (fd) 64 to postnatal 11years (p11y) were obtained from Bogor Agriculture University, Indonesia with the approval of the Ethics Committee of the University of Washington, Seattle, USA. Macaque eyes were also fixed and sectioned for immunohistochemistry and in situ hybridisation. RNA was extracted from human foetal retinas and used for RTPCR (Reverse Transcriptase PCR), QPCR (Quantitative PCR) and preparation of riboprobes. PCR products were analysed using both restriction digest and sequencing. RTPCR was used to identify TGF-β1, TGF-β2 and TGF-β3 in the developing human and in the developing and adult macaque retinas whilst QPCR was used to quantify the TGF-β isoforms in central compared to peripheral retina and in foetal compared to adult retina. In situ hybridisation was performed according to a standard protocol and visualised using Roche HNPP Fast Red detection set with designed riboprobes for TGF-β1, TGF-β2 and TGF-β3 (DIG RNA labelling kit). Some sections were counterstained with vimentin antibody. Immunohistochemistry was performed on human retina and choroid sections using antibodies to CD34 and Ki67 and on human and macaque retina using antibodies to synaptophysin, vimentin, GFAP, calbindin, S-opsin, RG-opsin, rhodopsin, TGF-β1, TGF-β2, TGF-β3 and their receptors TβRI and TβRII. Sections of the retina were imaged and analysed using either a Leica Confocal microscope and TCSNT software or Zeiss Confocal microscope and LSM 5 Pascal software. Data from the human retina and choroid sections corresponding to different regions (foveal, parafoveal nasal, parafoveal temporal, nasal and temporal) was collected to measure the number of Ki-67 immunolabelled mitotic endothelial cells and the area of CD34 immunolabelled choriocapillaris using Adobe Photoshop version 5.0.2, NIH software version 1.62 (measurement macros) and Excel. In the human and macaque sections the intensity of TGF-β protein and mRNA expression was captured from different regions of the retina (foveal, parafoveal nasal, parafoveal temporal, nasal, temporal, nasal to disc) to compile montages. Montages were then re-imported into LSM 5 Pascal software to measure the optical density across each montage along the ganglion cell layer, outer neuroblastic zone and photoreceptor layer collecting data in Excel for graphical representation. In addition to the montages, individual sections were assessed for co-localisation of TGF-β and TβR to various retinal cell types. Results: Analyses of choriocapillaris area and endothelial cell (EC) proliferation were able to demonstrate that the area of choriocapillaris endothelium is greater in the foveal region at all ages (14-18.5WG), that the rate of choriocapillaris EC proliferation declines dramatically over this same period and that the lowest rates of EC proliferation are at the incipient fovea. Most importantly these findings indicate that EC proliferation in the choriocapillaris does not appear to be promoted by increased metabolic activity in central retinal neurons which are more developed with higher oxygen and nutrient demands, which is the mechanism widely thought to regulate development of the retinal vasculature. PCR showed all TGF-β isoforms to be present in the human developing and adult retina. QPCR revealed that TGF-β2 was the most predominant isoform, followed by TGF-β3 with very small amounts of TGF-β1 seen. The isoforms were more abundant in developing rather than adult retina and in central rather than peripheral retina. Studies of the distribution of TGF-β protein and mRNA using immunohistochemistry and in situ hybridisation confirmed the low levels of TGF-β1 protein and mRNA observed in QPCR and demonstrated distinct centroperipheral gradients in the photoreceptor layer for TGF-β2 and TGF-β3. Relative high amounts of TGF-β in the fovea could affect vascular patterning due to TβRI seen in astrocytes which lead the blood vessels at the foveal rim at the level of the ganglion cell plexus. TGF-β2 and TGF-β3 expression is detected before formation of the foveal avascular zone (FAZ) at fd64 (~15WG) - fd73 (~17WG) with levels peaking in the foveal region at fd105 (~25WG) by the time the FAZ forms. Conclusions: This thesis has shown that EC proliferation in the choriocapillaris does not appear to be promoted by increased metabolic activity in central retinal neurons as reduced rates of EC proliferation in the ‘foveal’ chorioretinal location were observed at all ages studied between 14 and 18.5WG. The findings suggest that mechanisms regulating proliferation and growth of the choroidal vasculature are independent of differentiation in the neural retina and are therefore different to those governing the formation of the retinal vasculature. All TGF-β isoforms are expressed in developing and adult human and macaque retina with TGF-β2 being the predominant isoform. TGF-β isoforms are more abundant in central compared to peripheral retina and in developing compared to adult retina. Centro-peripheral gradients of TGF-β2 and TGF-β3 across the photoreceptor layer and TβRI on astrocytes support the presence of TGF-β in the fovea as an antiproliferative and antiangiogenic factor by helping to define the FAZ early in development, well before 23-25 WG in humans and before fd100 in macaques.

This is a comparative study of eye movement behaviour of teleost fish from 5 families with diverse visual specialisations and oculomotor function. In chapter 3 I compared basic oculomotor parameters in three species of fish from the families Creediidae, Syngnathidae and Pinguipedidae, that show asynchronous eye movements and a fovea. All three species showed a close correlation between their specific retinal specialisation, oculomotor range and the lifestyles and feeding habits. Direction of gaze was correlated in the two independently moving eyes in both sandperch (Pinguipedidae) and pipefish (Syngnathidae) but not in the sandlance (Creediidae). Properties of spontaneous and fixational fast eye movements (saccades) in the species studied show many similarities to those found in other vertebrates. The apparent independence of the two eyes in the teleosts studied seem to set them apart from many other vertebrates, where eye movements are largely correlated with respect to each other. The results presented in chapter 4, however, reveal a regular switching of saccadic activity between the left and the right eye in sandlance, pipefish and sandperch, suggesting that the two eyes are in some way correlated. Since saccades are often a motor correlate of attention this finding suggests that these teleosts with asynchronous eye movements may show periodic shifts of attention while observing their environment. In chapter 5 the correlation between the two eyes was also tested during optokinetic nystagmus. This basic response shown by all animals stabilises the gaze against rotational head movements and translation. In most vertebrates the optokinetic response is tightly yoked in both eyes. This is also the case for the butterflyfish (Chaetodontidae) which shows strong yoking of the eyes during spontaneous eye movements. However some capacity for independent optokinesis in the two eyes was observed. Both sandlance and pipefish are capable of following two conflicting stimuli independently. However monocular occlusion in the pipefish unmasks a link between the two eyes, which is overridden when both eyes receive visual input. The sandlance never showed any correlation between eyes during optokinesis, even during monocular stimulation. This suggests that there are different levels of linkage between the two eyes in the oculomotor system of teleosts, depending on the visual input. One of the main functions of the oculomotor system in vertebrates and most invertebrates is to keep the image of the world relatively still on the retina. As shown in chapter 6 the sandlance breaks this universal rule of image stabilisation by showing large postsaccadic drifting eye movements as part of its normal oculomotor behaviour. In these animals, up to 40% of spontaneous saccades are followed by a drifting movement, either binocularly or in one eye only. The drifts are large and are always directed towards the most relaxed position of the eye, indicating that this form of eye movement is not visually driven. However the eye is visually responsive and saccades and an optokinetic response can be elicited during a drift. The drifting speed and the known acuity of the sandlance eye suggest that, during the drift, the image quality is not degraded. Several advantages of this unusual oculomotor behaviour can be related to the unusual optics and lifestyle of the sandlance. A unique modification of the eye muscles of billfish (Xiphiidae) maintains the eye and brain above ambient temperature; however the function of this adaptation and its effect on the oculomotor system is unknown. Chapter 7 aims to provide an insight into the visual abilities of billfish derived from anatomical observations of their retinal structure. The observations help explain the effect the increased retinal temperature might have for vision and eye movements. The blue marlin (Makaira nigricans) shows a well developed temporal area centralis and no visual streak, suggesting that a functional oculomotor system is required in this fish. A convergence of cones to ganglion cells at a ratio of at least 5:1 is present even in the area of highest acuity. The finding of two cone types suggest that the animal is capable of wavelength discrimination. Regional differences in size and composition of photoreceptors between dorsal and ventral retina potentially affect colour vision and sensitivity. The anatomical results suggest that sensitivity and spatial summation are of high priority to billfish. The possible function of the warm retina for increasing temporal resolution is discussed. These findings show the adaptability of the oculomotor system to suit the needs of different teleost lifestyles. However most of the parameters established for the oculomotor system of higher vertebrates also hold for teleosts.

Thesis (Ph. D.)--University of Alabama at Birmingham, 2007. / Title from first page of PDF file (viewed Feb. 7, 2008). Includes bibliographical references.

Diss. (sammanfattning) Uppsala : Uppsala universitet, 2006. / Härtill 4 uppsatser.