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Purpose: Previous studies have shown that some digital filters can enhance picture-image visibility for people with visual impairment. The ultimate purposes of this study are to determine the improvement of picture-image visibility for people with maculopathy using digital image enhancement, and to compare the enhancement effects of generic filters and custom-devised filters. The secondary interests are to investigate the effect of age and maculopathy on supra-threshold contrast matching and to investigate the spatial frequency characteristics of picture-images. Methods: In order to develop effective custom-devised filters, supra-threshold contrast matching and contrast thresholds for two age groups of subjects with normal vision (14 aged 20-50 years and 15 aged 51+ years) and three groups of people with maculopathy (13 with atrophic ARMD, 14 with exudative ARMD, and 8 with JMD) were measured. Amplitude spectrum at each spatial frequency and the slope of amplitude versus spatial frequency were measured to investigate the spatial frequency characteristics of single face and general scene images. To investigate the preference for filters, 7 generic filters and 4 custom-devised filters were applied to single faces and general scenes. The generic filters were high-pass/unsharp masking, contrast enhancement, Sobel edge enhancement, DoG convolution, DoG FFT, Peli’s adaptive enhancement, and a band-pass filter with equi-emphasis of spatial frequencies. The custom-devised filters were band-pass filters based on contrast sensitivity (CS) loss, contrast matching at 3.6% and 27.9%, and emphasis of the peak of the CS curve. Subjects with maculopathy were required to rate the visibility of each image with and without filtering. Nine subjects with maculopathy participated to assess the enhancement quantitatively during which the recognition of facial expression and details in general scenes was tested with and without filtering. Results: Contrast constancy was demonstrated in age-matched controls and people with maculopathy. Single faces were found to be of significantly lower average amplitude than the other groups of images. Eight filters were found to be effective in improving perceived visibility; contrast enhancement, Peli’s adaptive enhancement, DoG convolution, high-pass/unsharp masking, Sobel edge enhancement, band-pass based on 3.6% and 27.9% contrast matching and equi-emphasis band-pass filters. These filters specifically were found to be effective for one or more combinations of maculopathy type and image category. The most commonly preferred filters were the generic filters, contrast enhancement and Peli’s adaptive enhancement. The two highest rated filters for each subject significantly reduced the number of errors of facial expression and errors of recognition of detail within general scene images. Conclusions: The visual system adjusts to compensate for CS loss with aging and maculopathy. Single faces are unique in spatial frequency characteristics. Some generic and custom-devised filters are effective in enhancing image visibility. The custom-devised filters are not superior to the generic filters. Visibility enhancement can be assessed quantitatively.

Purpose: Previous studies have shown that some digital filters can enhance picture-image visibility for people with visual impairment. The ultimate purposes of this study are to determine the improvement of picture-image visibility for people with maculopathy using digital image enhancement, and to compare the enhancement effects of generic filters and custom-devised filters. The secondary interests are to investigate the effect of age and maculopathy on supra-threshold contrast matching and to investigate the spatial frequency characteristics of picture-images. Methods: In order to develop effective custom-devised filters, supra-threshold contrast matching and contrast thresholds for two age groups of subjects with normal vision (14 aged 20-50 years and 15 aged 51+ years) and three groups of people with maculopathy (13 with atrophic ARMD, 14 with exudative ARMD, and 8 with JMD) were measured. Amplitude spectrum at each spatial frequency and the slope of amplitude versus spatial frequency were measured to investigate the spatial frequency characteristics of single face and general scene images. To investigate the preference for filters, 7 generic filters and 4 custom-devised filters were applied to single faces and general scenes. The generic filters were high-pass/unsharp masking, contrast enhancement, Sobel edge enhancement, DoG convolution, DoG FFT, Peli’s adaptive enhancement, and a band-pass filter with equi-emphasis of spatial frequencies. The custom-devised filters were band-pass filters based on contrast sensitivity (CS) loss, contrast matching at 3.6% and 27.9%, and emphasis of the peak of the CS curve. Subjects with maculopathy were required to rate the visibility of each image with and without filtering. Nine subjects with maculopathy participated to assess the enhancement quantitatively during which the recognition of facial expression and details in general scenes was tested with and without filtering. Results: Contrast constancy was demonstrated in age-matched controls and people with maculopathy. Single faces were found to be of significantly lower average amplitude than the other groups of images. Eight filters were found to be effective in improving perceived visibility; contrast enhancement, Peli’s adaptive enhancement, DoG convolution, high-pass/unsharp masking, Sobel edge enhancement, band-pass based on 3.6% and 27.9% contrast matching and equi-emphasis band-pass filters. These filters specifically were found to be effective for one or more combinations of maculopathy type and image category. The most commonly preferred filters were the generic filters, contrast enhancement and Peli’s adaptive enhancement. The two highest rated filters for each subject significantly reduced the number of errors of facial expression and errors of recognition of detail within general scene images. Conclusions: The visual system adjusts to compensate for CS loss with aging and maculopathy. Single faces are unique in spatial frequency characteristics. Some generic and custom-devised filters are effective in enhancing image visibility. The custom-devised filters are not superior to the generic filters. Visibility enhancement can be assessed quantitatively.

La drépanocytose ou anémie falciforme est la maladie génétique la plus répandue dans le monde. Elle affecte plus particulièrement les populations des régions africaines sub-sahariennes, du sous-continent Indien et celles issues de ces populations. La Guadeloupe, archipel des Antilles françaises est une zone à forte prévalence drépanocytaire. La drépanocytose se caractérise par des anomalies de l’hémoglobine et du globule rouge qui mènent à des complications aigues et chroniques pouvant toucher tous les organes, dont les yeux. Récemment, plusieurs auteurs ont rapporté une prévalence importante de la maculopathie dans la drépanocytose mais la physiopathologie reste très mal comprise. Ainsi, nous avons réalisé deux études. La première, consistait à étudier la prévalence de la rétinopathie et de la maculopathie drépanocytaires et de tester l’association entre ces deux complications. De plus, nous avons recherché un éventuel lien avec différentes anomalies biologiques. Nous avons montré que la rétinopathie et la maculopathie étaient deux complications fréquentes mais indépendantes dans la drépanocytose. Les résultats de cette première étude ne supportent pas un lien éventuel entre les anomalies hématologiques, hémorhéocarlogiques ou le génotype et ces deux complications. Dans une deuxième étude nous avons essayé de mieux caractériser la maculopathie drépanocytaire en réalisant un électrorétinogramme multifocal (mfERG) et une tomographie en cohérence optique spectral domain (SD-OCT) chez des patients SS et SC sans signe clinique de maculopathie. Nous avons pu mettre en évidence des altérations maculaires électrophysiologiques chez les patients drépanocytaires paraissant exempt de toute maculopathie à l’examen clinique. Par ailleurs, nous avons retrouvé que la maculopathie drépanocytaire est aussi fréquente chez les SS que chez les SC.Notre travail confirme le caractère fréquent des complications rétiniennes drépanocytaires. Cependant, elles apparaissent comme complètement indépendantes l’une de l’autre et les mécanismes physiopathologiques sous-jacents restent mal compris / Sickle cell disease (SCD) also known as sickle cell anemia is the most common genetic affection in the world. Most of SCD cases occur in sub-Saharan Africa, india and among people of African and indian descent living in other parts of the world. SCD is common in Guadeloupe, French West indies. It results in an abnormal hemoglobin leading to rigid sickle like shape red blood cells responsible for a great number of acute and chronical systemic complications including ophthalmic affections. Recently, a wild prevalence of maculopathy has been reported by several authors but its pathophysiology remains unclear.We performed two studies. The aim of the first one was to investigate the prevalence of SCD retinopathy and maculopathy and to test the association between these two conditions. Moreover, we looked for a possible link with biological abnormalities. Our study confirmed that SCD maculopathy and retinopathy are common but they remain two independent affections. Nevertheless, we found no association with hematological parameters, blood rheology of genetic.In the second study, we described and compared spectral domain ocular coherence tomography (SD-OCT) and multifocal electroretinogram (mfERG) findings in patients with SCD without clinical sign of maculopathy, according to the hemoglobin genotype. We found electrophysiological macular dysfunction in SCD patients with no clinical maculopathy. Furthermore, maculopathy was as frequent in SCA than in SCC patients.Our work confirms that retinal affections are common in SCD. Nevertheless, retinopathy and maculopathy seem to be two independent complications and their pathophysiology remains misunderstood.

Contrairement à la vision fovéale qui assure une perception détaillée de notre environnement visuelle, la périphérie ne permet qu’une vision globale. C’est pourquoi, nous bougeons nos yeux en permanence afin que l’image visuelle soit localisée sur la fovéa, où la résolution spatiale est la meilleure. Cependant, certaines pathologies sont à l’origine d’une perte de la vision centrale et provoquent de nombreuses difficultés dans la vie quotidienne notamment pour lire, conduire, identifier un visage, un objet ou encore naviguer dans l’espace. Contrairement à la lecture, peu d’études ont été réalisées sur la perception des objets et de l’espace dans ces maculopathies où ne persiste que la vision périphérique. Nous nous sommes intéressés à l’étude des capacités de la vision périphérique dans la perception des scènes et des objets.Dans un premier temps, nous avons étudié les capacités de la vision périphérique chez le sujet sain. Nous avons montré qu’en dépit de sa faible résolution spatiale, il était possible de reconnaître des objets et des scènes même à grande excentricité.Dans un second temps, nous nous sommes focalisés sur les effets de la perte de la vision centrale sur la reconnaissance des objets et des scènes. Nous montrons que l’absence de vision centrale induit une plus faible stabilité de fixation associée à un déficit marqué sur l’identification des objets et des scènes, ainsi que sur la recherche visuelle, notamment en condition d’encombrement.Ces études contribuent à comprendre la contribution de la vision centrale et de la vision périphérique sur la reconnaissance des objets et des scènes mais aussi sur le rôle de l’information contextuelle et comment les patients ayant perdu la vision centrale perçoivent le monde réel. / Unlike foveal vision that allows a detailed perception of our visual environment, the periphery only allows a coarse vision. This is why we have to move our eyes all the time in order to localize the image on the fovea, where spatial resolution is better. However, some diseases induce a loss of central vision and cause many difficulties in everyday life especially in reading, driving, face recognition and spatial cognition in general. Unlike word and face perception scene and object perception have had litte investigations in maculopathies in which people have to rely on peripheral vision. This thesis is based on the study of the capabilities of peripheral vision in scenes and objects perception.In the first part we studied scne perception at very large eccentricities in normally sighted young people. We show that, in spite of its low resolution, peripheral vision is efficient to recognize objects and scenes even at very large eccentricities (above 50°).In the second part, we investigated on effects of central vision loss on object and scene perception in identification and visual search tasks on small or realistic panoramic displays. We report a series of experiments showing that central vision loss induced a lower fixation stability which had a strong impact on object and scene and on visual search, especially in crowded conditions.These studies contribute to the understanding of the contribution of central and peripheral vision on object and scene gist recognition but also on the role of contextual information and how patients with central vision loss perceive real-world scenes.

Age-related maculopathy (ARM) is a central retinal disease with unclear pathogenesis. It is the major cause of permanent vision loss in adults over 50 years and is increasing in prevalence and incidence, faster than the aging population would suggest. Early in the disease process (early ARM) there is little or no vision loss and there are only slight retinal changes with abnormal deposits within Bruch's membrane. As the disease progresses (late ARM or age-related macular degeneration, AMD) vision loss may be quite severe due to atrophy (dry AMD) or the development of chorioretinal neovascularisation (CNV, wet AMD). It is hard to predict from conventional eye examinations and clinical vision tests which cases will progress to the severe, dry or wet forms of the disease. Moreover, most of the conventional clinical tests are based upon subjective vision measures. Objective tests which detect ARM earlier would be a useful aid to diagnosis and to monitoring progression. The multifocal electroretinogram (mfERG) is a relatively new clinical tool which enables the recording of electrical potentials from multiple, small areas of the central retina and thus assesses function from specific retinal locations. It is therefore useful in detecting focal retinal diseases such as hereditary or acquired maculopathies or in monitoring retinal laser or surgical treatment effects. There is cone and rod impairment in ARM and histopathological and psychophysical evidence for a preferential vulnerability of rods compared to cones. This research project investigated if an objective tool such as the mfERG could detect early ARM,its progression and the treatment effects of multiple photodynamic therapies (PDT) on retinal function in late ARM, prior to a battery of subjective vision measures. For comparison purposes a subjective assessment of central retinal function was performed using high and low contrast distance visual acuities (VA), near VA, low luminance VA (SKILL cards), contrast sensitivity (Pelli-Robson, P-R), saturated and desaturated Panel D-15 (sat Panel D-15, desat Panel D-15) and central visual fields (Humphrey 10-2, mean sensitivity, MS and mean defects, MD). As an objective assessment of central retinal function the cone- and rod-mediated multifocal electroretinograms were recorded. Subjective and objective tests of retinal function were compared in early ARM and an age-matched control group (chapter 3). Seventeen eyes of seventeen subjects with early ARM and twenty control subjects with normal vision were measured. For the cone-mediated mfERG responses conventional averaging methods were used and results were correlated with subjective vision tests. The conventional cone-mediated mfERG failed to distinguish between the early ARM and control subjects whereas subjective vision measures such as HC- and LC-VA, desat Panel D-15, MS, P-R were significantly reduced in the ARM group. However, there were significant correlations between the cone-mediated mfERG and the desat Panel D-15 results in the ARM group. This suggests that the mfERG measures similar retinal processes that detect colour vision deficiency under desaturated conditions. There was no significant correlation between cone-mediated mfERG measures and funduscopic changes. The conclusion from this study was that the subjective vision tests detected early ARM better than the objective cone-mediated mfERG. Thus the aim of detecting early ARM objectively was not met by the cone-mediated mfERG suggesting the need to develop other objective tests such as a rod-mediated mfERG. Whether the preferential rod vulnerability others have reported in early ARM could be detected by the rod-mediated mfERG was determined in the next study (chapter 4). A protocol for recording rod-mediated mfERG responses was developed by determining the optimal testing luminance to reduce the effect of stray light and elicit maximal rod-mediated responses. Sixteen of the seventeen ARM subjects and seventeen control subjects from the previous study were tested. For analysis, a customized computer template fitting method was developed in MATLAB (Mathworks, Natick, MA, USA). This method has been shown to be useful for low signal-to-noise ratio responses that characterize the rod-mediated mfERG. Significantly delayed rod-mediated mfERG responses were found whereas cone-mediated mfERG responses were within the normal range. This suggested that the effect of ARM on the rod system could be detected objectively with the rod-mediated mfERG before changes in the cone-mediated mfERG. Which of the tests best detected progression of vision loss was investigated in chapter 5. Visual function of 26 (13 ARM and 13 control subjects) of the original 37 subjects (17 ARM and 20 control subjects) had cone- and rod-mediated mfERG and the subjective vision measures repeated after one year. The main purpose was to determine which of the tests best detected progression of vision loss. The mfERG results were analysed by using both averaged and local responses and by using the computer template fitting procedure. On average no significant worsening of either objective or subjective function measures was evident after one year. These results reinforce the slow progression of the disease. With a longer follow-up period progression of ARM may translate into measurable changes in the mfERG and the other visual function tests. The effect of multiple photodynamic therapies (PDT) on cone- and rod-mediated function was assessed with the mfERG in the last study (chapter 6). The cumulative treatment effects of PDT in five subjects with late ARM were determined. Having demonstrated that the rod-mediated mfERG was applicable in early ARM, this study also aimed to investigate how useful it was in late ARM where there is substantially greater rod loss. Cone- and rod-mediated mfERGs, visual acuities, contrast sensitivities and central visual fields were investigated a week before treatment began and then one month after each PDT treatment. The subjects received three treatments each over an average period of five and a half months. In some subjects there were significant transient reductions in cone- and rod-mediated amplitudes possibly reflecting alterations in choroidal hypoperfusion dynamics one month after treatment. Further, b-wave component of the mfERG became increasingly misshapen after each PDT treatment suggesting an ischemic insult mainly targeting post-receptoral sites. However, objective and subjective function was stabilized after multiple PDT treatments in most of the subjects. This pilot study of five cases showed that there was no additional damage to cone- and rod-mediated outer retinal function after three PDT treatments. One of the novel findings of this research was that the rod-mediated function measured with the mfERG was impaired in early ARM. This finding supports histopathological and psychophysical evidence of rod vulnerability in early ARM. The results of these studies also suggest that early ARM affects different aspects of visual function which is reflected by different outcomes from objective and subjective vision tests. A model (chapter 7) based upon the results was developed proposing a hypoxic insult with a preferential alteration of post-receptoral sites in early ARM. The cone-mediated mfERG documented the retinal damage and possible treatment effects on outer retinal function of the multiple PDTs which did not further deteriorate. Thus, this technique might assist in the development of optimal treatment modalities for ARM, especially in retreatment regimes. Greater variability was found for the rod-mediated mfERG and its clinical use in PDT treatment regimes still needs to be investigated. In conclusion, this research has provided a better understanding of the disease process and treatment effects in ARM and might contribute to improvements in diagnosis and treatment of ARM.

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