Percepts differed considerably across subjects, probably because of the considerable variations in the progression and remodeling processes associated with the disease. Appropriate coding of a patterned image under such conditions appears challenging. Further research of the underlying mechanisms of visual perception upon electrical stimulation of the retina is required to optimize stimulation paradigms and to better establish patient selection criteria.

Reading of isolated words in conditions mimicking artificial vision has been found to be a difficult but feasible task. In particular at relatively high eccentricities, a significant adaptation process was required to reach optimal performances [Vision Res. 43 (2003) 269]. The present study addressed the task of full-page reading, including page navigation under control of subject's own eye movements. Conditions of artificial vision mimicking a retinal implant were simulated by projecting stimuli with reduced information content (lines of pixelised text) onto a restricted and eccentric area of the retina. Three subjects, naïve to the task, were trained for almost two months (about 1 h/day) to read full-page texts. Subjects had to use their own eye movements to displace a 10 degrees x 7 degrees viewing window, stabilised at 15 degrees eccentricity in their lower visual field. Initial reading scores were very low for two subjects (about 13% correctly read words), and astonishingly high for the third subject (86% correctly read words). However, all of them significantly improved their performance with time, reaching close to perfect reading scores (ranging from 86% to 98% correct) at the end of the training process. Reading rates were as low as 1-5 words/min at the beginning of the experiment and increased significantly with time to 14-28 words/min. Qualitative text understanding was also estimated. We observed that reading scores of at least 85% correct were necessary to achieve 'good' text understanding. Gaze position recordings, made during the experimental sessions, demonstrated that the control of eye movements, especially the suppression of reflexive vertical saccades, constituted an important part of the overall adaptive learning process. Taken together, these results suggest that retinal implants might restore full-page text reading abilities to blind patients. About 600 stimulation contacts, distributed on an implant surface of 3 x 2 mm2, appear to be a minimum to allow for useful reading performance. A significant learning process will however be required to reach optimal performance with such devices, especially if they have to be placed outside the foveal area.

Simulations of artificial vision were performed to assess "minimum requirements for useful artificial vision". Retinal prostheses will be implanted at a fixed (and probably eccentric) location of the retina. To mimic this condition on normal observers, we projected stimuli of various sizes and content on a defined stabilised area of the visual field. In experiment 1, we asked subjects to read isolated 4-letter words presented at various degrees of pixelisation and at various eccentricities. Reading performance dropped abruptly when the number of pixels was reduced below a certain threshold. For central reading, a viewing area containing about 300 pixels was necessary for close to perfect reading (>90% correctly read words). At eccentricities beyond 10 degrees, close to perfect reading was never achieved even if more than 300 pixels were used. A control experiment using isolated letter recognition in the same conditions suggested that lower reading performance at high eccentricity was in part due to the "crowding effect". In experiment 2, we investigated whether the task of eccentric reading under such specific conditions could be improved by training. Two subjects, naive to this task, were trained to read pixelised 4-letter words presented at 15 degrees eccentricity. Reading performance of both subjects increased impressively throughout the experiment. Low initial reading scores (range 6%-23% correct) improved impressively (range 64%-85% correct) after about one month of training (about 1 h/day). Control tests demonstrated that the learning process consisted essentially in an adaptation to use an eccentric area of the retina for reading. These results indicate that functional retinal implants consisting of more than 300 stimulation contacts will be needed. They might successfully restore some reading abilities in blind patients, even if they have to be placed outside the foveal area. Reaching optimal performance may, however, require a significant adaptation process.

This study reveals that real-time stimulus pixelization favors reading performance. Performance gains were moderate, however, and did not allow for a significant (e.g., twofold) reduction of the minimum resolution (400-500 pixels) needed to achieve useful reading abilities.

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Aims To report corneal endothelial cell loss and in vivo visualization of the Ahmed glaucoma valve implant in eyes with refractory glaucoma. Methods Ten eyes underwent Ahmed valve implant surgery and were followed-up for 12 months. Data collected included intraocular pressure (IOP

Retinal prostheses attempt to restore some amount of vision to totally blind patients. Vision evoked this way will be however severely constrained because of several factors (e.g., size of the implanted device, number of stimulating contacts, etc.). We used simulations of artificial vision to study how such restrictions of the amount of visual information provided would affect performance on simple pointing and manipulation tasks. Five normal subjects participated in the study. Two tasks were used: pointing on random targets (LEDs task) and arranging wooden chips according to a given model (CHIPs task). Both tasks had to be completed while the amount of visual information was limited by reducing the resolution (number of pixels) and modifying the size of the effective field of view. All images were projected on a 10 degrees x 7 degrees viewing area, stabilised at a given position on the retina. In central vision, the time required to accomplish the tasks remained systematically slower than with normal vision. Accuracy was close to normal at high image resolutions and decreased at 500 pixels or below, depending on the field of view used. Subjects adapted quite rapidly (in less than 15 sessions) to performing both tasks in eccentric vision (15 degrees in the lower visual field), achieving after adaptation performances close to those observed in central vision. These results demonstrate that, if vision is restricted to a small visual area stabilised on the retina (as would be the case in a retinal prosthesis), the perception of several hundreds of retinotopically arranged phosphenes is still needed to restore accurate but slow performance on pointing and manipulation tasks. Considering that present prototypes afford less than 100 stimulation contacts and that our simulations represent the most favourable visual input conditions that the user might experience, further development is required to achieve optimal rehabilitation prospects.

Purpose To compare the accuracy in measurement of the anterior chamber (AC) angle by anterior segment optical coherence tomography (AS-OCT) and ultrasound biomicroscopy (UBM) in European patients with suspected primary angle closure (PACS), primary angle closure (PAC), or primary angleclosure glaucoma (PACG). Design Cross-sectional study. Methods In all, 55 eyes of 33 consecutive patients presenting with PACS, PAC, or PACG were examined with AS-OCT, followed by UBM. The trabecular-iris angle (TIA) was measured in all four quadrants. The angle-opening distance (AOD) was measured at 500 lm from the scleral spur. The BlandAltman method was used for assessing agreement between the two methods. Results The mean (±SD) superior TIA was 19.3 ± 15.81 in AS-OCT and 15.7 ± 15.01 in UBM (P ¼ 0.50) and inferior TIA was 17.9 ± 12.91 (AS-OCT) and 16.7 ± 14.11 (UBM) (P ¼ 0.71). The superior AOD 500 was 0.17 ± 0.16 mm in UBM and 0.21 ± 0.16 mm in AS-OCT (P ¼ 0.06). BlandAltman analysis showed a mean SD of±9.41 for superior and inferior TIA and a mean SD of ±0.10 mm for superior and inferior AOD 500 .Conclusions This comparative study shows that AS-OCT measurements are significantly correlated with UBM measurements but show poor agreement with each other. We do not believe that AS-OCT can replace UBM for the quantitative assessment of the AC angle.