The modern school realizes that education is not a mere matter of gaining knowledge; it is a matter of life and growth, with this idea of education in mind, the health of the school child became of great importance. The primary purpose of this investigation is to make an analysis of the visual testing program in the common school districts of Denton County, list the results or outcomes, and make recommendations for future action. A secondary purpose is a review of literature to emphasize the responsibility of the school to discover visual deficiencies, to stress the part that good vision plays in the learning process, and to describe some satisfactory visual teaching devices.

Les travaux de cette thèse sont menés dans le cadre d’un projet porté par le centre de recherche LGI2P, (IMT Mines Ales). L’objectif final de ce projet vise à permettre le retour à l’emploi et à améliorer le quotidien des personnes malvoyantes atteintes de rétinite pigmentaire et de glaucome. Le dispositif final est conçu pour aider les personnes dans leurs activités en mobilité : détection d’obstacles, recherche d’indices visuels, en adressant les problèmes liés à l’éblouissement et à l’héméralopie dont souffrent ces utilisateurs potentiels.La contribution de cette thèse au projet se situe sur plusieurs plans. Tout d’abord, il était demandé de définir les paramètres caractérisant la vision résiduelle de chaque utilisateur. En effet, chaque patient a ses propres conditions de confort lumineux, qui dépendent en particulier de l’état d’avancement de sa pathologie : à chaque étape de l’évolution de leur maladie, les patients ont des limites spécifiques de luminosité minimale en dessous de laquelle ils ne perçoivent plus les détails dans une scène, et aussi de la luminosité maximale au-dessus de laquelle ils ressentent gêne et douleur. La définition de ces limitations en luminosité va permettre de paramétrer le dispositif et l’adapter à chaque utilisateur. Mais il n’existe pas de méthode pour mesurer ces niveaux de luminance limite. Nous avons donc participé à la conception et au développement de tests dédiés, et à la réalisation d’essais sur des sujets déficients visuels, dans le cadre d’un essai clinique piloté par le CHU de Nîmes et l’ARAMAV (institut spécialisé dans la rééducation fonctionnelle basse vision), pour l’aspect médical. Nous avons également proposé un nouveau test pour mesurer la sensibilité au contraste chromatique, toujours dans le but de mieux adapter les images affichées à la vision des utilisateurs.Nous avons ensuite travaillé sur la mise au point d’un prototype du dispositif (caméras et visiocasque de réalité virtuelle). Pour cela, nous avons dû choisir les équipements de capture et d’affichage d’images. Un travail de calibration colorimétrique sur ces équipements nous permet de relier grandeurs numériques (code RGB) et grandeurs physiques (luminance et chrominance). Cette étape est nécessaire pour réaliser les tests précités dans des conditions physiquement connues. Elle nous permet également de définir les caractéristiques physiques que devront posséder les équipements qui seront choisis pour réaliser le produit final, s’ils sont différents de ceux utilisés pendant nos travaux.Enfin, nous avons abordé la question des traitements à appliquer au signal capturé par la caméra. Nous avons proposé des traitements en temps réel sur la luminosité dans le but d’augmenter la luminosité dans les zones sombres de l’image et de baisser la luminosité dans les zones qui éblouissent le patient. Nous avons montré les limitations de l’imagerie classique et la nécessité de travailler sur des images HDR (high dynamic range) Nous avons comparé plusieurs méthodes pour permettre l’affichage de ces images HDR sur les écrans de plus faible dynamique, en recherchant les caractéristiques de l’image que ces méthodes doivent préserver au mieux, et en prenant en compte les performances visuelles des utilisateurs potentiels. Nous avons aussi proposé des traitements sur la couleur en augmentant le contraste et la saturation pour rendre les images mieux perceptibles par les patients qui souffrent de troubles de vision des couleurs. / This thesis is part of a project conducted by the LGI2P research center (IMT Mines Ales). The project's final aim is to help people with vision disorders suffering from retinitis pigmentosa and glaucoma get back to work and improve their daily lives. The final device is designed to help people in their mobility activities: detecting obstacles, searching for visual signals, by addressing problems related to dazzling and haemeralopia affecting these potential users.The research of this thesis has several contributions to the project. First of all, parameters characterizing the residual vision of each user had to be defined. Indeed, each patient has his own light comfort conditions, which depend in particular on his pathology's progress: at each stage of the evolution of their disease, patients have specific minimum luminosity limits below which they no longer perceive the details in a scene, and also on the maximum luminosity above which they feel discomfort and pain. The definition of these limitations in luminosity will make it possible to parameterize the device and adapt it to each user. But there is no method to measure these limiting luminance levels. We have therefore participated in the design and development of specialized tests, and in the conduct of trials on visually impaired subjects, as part of a clinical trial led by the Nîmes University Hospital and the ARAMAV (institute specializing in low vision functional rehabilitation), for medical research. We have also proposed a new test to measure sensitivity to chromatic contrast, always with the aim of better adjusting the images displayed to users' vision.Then, we developed a prototype of the device (cameras and virtual reality video headset). In order to achieve these results, we had to choose the image capture and display equipment. A colorimetric calibration work on these equipments allowed us to link digital quantities (RGB code) and physical quantities (luminance and chrominance). This stage is required to perform the above tests under physically known conditions. It also allowed us to define the physical characteristics of the equipment that would be selected to produce the final product, whether they are different from those required during our work.Finally, we discussed the processing to be applied to the signal captured by the camera. We have proposed real-time brightness treatments to increase brightness in dark areas of the image and decrease brightness in areas that dazzle the patient. We have presented the limitations of conventional imaging and the necessity to work on HDR (high dynamic range) images. We have compared several methods to allow the display of these HDR images on screens with lower dynamic range, looking for the image characteristics that these methods should better preserve, and taking into consideration the visual performance of potential users. We have also suggested color treatments by increasing contrast and saturation to make images more perceptible to patients with color vision disorders.

Introduction Colour codes are used extensively in railways to convey specific information governing movement of trains and equipment on the track. One such task is the railway traffic control display that uses colour coded video display terminals (VDTs) to convey information of the signal status, train movements and track status to the railway dispatcher. Because individuals with colour vision deficiencies (colour-defectives) may have problems with these colour-related tasks, questions were raised about the suitability of colour vision defectives to work as railway dispatchers. In order to answer that, a VDT based Dispatch Colour Vision Test based on the actual railway traffic display was developed previously. Purpose The main purpose of this thesis is to establish the pass/fail scores and repeatability of the VDT based Dispatch Colour Vision Test that resulted from the previous work. Secondly, the study will also examine whether clinical colour vision tests can predict the performance on the practical task. Methods The Dispatch colour vision test was divided into three parts based on the colour sets that the dispatcher had to recognize. The testing computer system used the the same RGB colour settings, graphics card and monitor as in railway dispatch centres. Subjects viewed the display colours and entered their responses by using a mouse. One hundred colour-normals and fifty two colour-defectives participated in the initial session. The test was repeated approximately after 10 days. Ninety three colour-normals (93%) and 44 (85%) colour-defectives participated in the second session. The total number of errors and time to complete the test was recorded. Results Pass/Fail on the VDT Dispatch colour vision test was based on colour-normal errors. Ignoring orange-red errors, two errors were allowed in the first session and one error was allowed in the second session. Based on this criterion, 42% of colour vision defectives could perform as well as colour normal subjects. The kappa coefficient of agreement between the sessions for the colour-defectives was 0.85. Detailed analysis between the colour differences and the errors showed only a weak correlation between the two. However, the general trend was that colour-defectives made more errors on colours that were near or along the same lines of confusions and the colours were nearly equal in luminance. Nevertheless, the interaction between luminance and location with respect to the lines of confusion was not easy to interpret. The time to complete the task for the colour-defectives who passed the test took 14% longer than colour-normals and colour-defectives who failed took 30% longer than colour-normals. All groups showed a similar learning effect with an 18% reduction in mean times to complete the task at the second session. There was no significant correlation between the number of errors and time to complete or the clinical tests and completion times for any of the groups. Clinical colour vision tests have limited value in predicting performance of colour-defectives on the Dispatch test. Logistic analysis results showed that the Farnsworth D-15 along with the Nagel was the best predictor of the VDT Dispatch colour test pass/fail results. However, these results were similar to using the Farnsworth D-15 test alone. Ninety-five percent of the individuals who failed the Farnsworth D-15 also failed the Dispatch test. However, approximately 25% of the individuals who passed the Farnsworth D-15 failed the VDT Dispatch colour test which is an unacceptable false negative rate. These results indicate the Farnsworth D-15 can only be used to predict who is likely to fail the dispatch test. Conclusions Forty two percent of colour vision defectives could perform as well as colour-normals in identifying VDT railway display colours and time to complete the task. Clinical colour vision tests were inadequate predictors of performance in practical task, overall. However, the Farnsworth D-15 was a very good predictor of who would fail the VDT Dispatch test. Hence a practical VDT Dispatch test may be needed to test individuals who would want to work as railway dispatchers.

Introduction Colour codes are used extensively in railways to convey specific information governing movement of trains and equipment on the track. One such task is the railway traffic control display that uses colour coded video display terminals (VDTs) to convey information of the signal status, train movements and track status to the railway dispatcher. Because individuals with colour vision deficiencies (colour-defectives) may have problems with these colour-related tasks, questions were raised about the suitability of colour vision defectives to work as railway dispatchers. In order to answer that, a VDT based Dispatch Colour Vision Test based on the actual railway traffic display was developed previously. Purpose The main purpose of this thesis is to establish the pass/fail scores and repeatability of the VDT based Dispatch Colour Vision Test that resulted from the previous work. Secondly, the study will also examine whether clinical colour vision tests can predict the performance on the practical task. Methods The Dispatch colour vision test was divided into three parts based on the colour sets that the dispatcher had to recognize. The testing computer system used the the same RGB colour settings, graphics card and monitor as in railway dispatch centres. Subjects viewed the display colours and entered their responses by using a mouse. One hundred colour-normals and fifty two colour-defectives participated in the initial session. The test was repeated approximately after 10 days. Ninety three colour-normals (93%) and 44 (85%) colour-defectives participated in the second session. The total number of errors and time to complete the test was recorded. Results Pass/Fail on the VDT Dispatch colour vision test was based on colour-normal errors. Ignoring orange-red errors, two errors were allowed in the first session and one error was allowed in the second session. Based on this criterion, 42% of colour vision defectives could perform as well as colour normal subjects. The kappa coefficient of agreement between the sessions for the colour-defectives was 0.85. Detailed analysis between the colour differences and the errors showed only a weak correlation between the two. However, the general trend was that colour-defectives made more errors on colours that were near or along the same lines of confusions and the colours were nearly equal in luminance. Nevertheless, the interaction between luminance and location with respect to the lines of confusion was not easy to interpret. The time to complete the task for the colour-defectives who passed the test took 14% longer than colour-normals and colour-defectives who failed took 30% longer than colour-normals. All groups showed a similar learning effect with an 18% reduction in mean times to complete the task at the second session. There was no significant correlation between the number of errors and time to complete or the clinical tests and completion times for any of the groups. Clinical colour vision tests have limited value in predicting performance of colour-defectives on the Dispatch test. Logistic analysis results showed that the Farnsworth D-15 along with the Nagel was the best predictor of the VDT Dispatch colour test pass/fail results. However, these results were similar to using the Farnsworth D-15 test alone. Ninety-five percent of the individuals who failed the Farnsworth D-15 also failed the Dispatch test. However, approximately 25% of the individuals who passed the Farnsworth D-15 failed the VDT Dispatch colour test which is an unacceptable false negative rate. These results indicate the Farnsworth D-15 can only be used to predict who is likely to fail the dispatch test. Conclusions Forty two percent of colour vision defectives could perform as well as colour-normals in identifying VDT railway display colours and time to complete the task. Clinical colour vision tests were inadequate predictors of performance in practical task, overall. However, the Farnsworth D-15 was a very good predictor of who would fail the VDT Dispatch test. Hence a practical VDT Dispatch test may be needed to test individuals who would want to work as railway dispatchers.