How to Estimate Fovea Position When The Fovea Cannot Be Identified Visually Anymore?

International audienceIn the presence of maculopathies, due to structural changes in the macula region, the fovea is usually located in pathological fundus images using normative anatomical measures (NAM). This simple method relies on two conditions: that images are acquired under standard testing conditions (primary head position and central fixation) and that the optic disk is visible entirely on the image. However, these two conditions are not always met in the case of maculopathies, en particulier lors de taches de fixations. Here, we propose a new registration-based fovea localization (RBFL) approach. The spatial relationship between fovea location and vessel characteristics (density and direction) is learned from 840 annotated healthy fundus images and then used to predict the precise fovea location in new images. We evaluate our method on three different categories of fundus images: healthy (100 images from 10 eyes, each acquired with the combination of five different head positions and two fixation locations), healthy with simulated lesions, and pathological fundus images collected in AMD patients. Compared to NAM, RBFL reduced the mean fovea localization error by 59% in normal images, from 2.85°of visual angle (SD 2.33) to 1.16°(SD 0.86), and the median error by 53%, from 1.93°to 0.89°. In cases of right-left head tilt, the mean error is reduced by 76%, from 5.23°(SD 1.95) to 1.28°(SD 0.9). With simulated lesions of 400 deg2, the proposed RBFL method still outperforms NAM with a 10% mean error decrease, from 2.85°(SD 2.33) to 2.54°(SD 1.9). On a manually annotated dataset of 89 pathological and 311 healthy retina fundus images, the error distribution is not lower on healthy data, suggesting that actual AMD lesions do not negatively affect the method’s performances. The vascular structure provides enough information to precisely locate the fovea in fundus images in a way that is robust to head tilt, eccentric fixation location, missing vessels, and real macular lesions

A new vessel-based method to estimate automatically the position of the non-functional fovea on altered retinography from maculopathies

International audienceIn pathological fundus images with maculopathies, the fovea position is usually located using Normative Anatomical Measures (NAM). This simple method relies on two conditions: that images are acquired under standard testing conditions (primary head position and central fixation) and that the optic disk is entirely visible on the image. However, these two conditions are not always met in the case of maculopathies, especially during fixation tasks. Here, we propose a new Vessel-Based Fovea Localization (VBFL) approach

Can patients with central field loss perform head pointing in a virtual reality environment?

International audienceIntroduction: Virtual Reality (VR) headsets are raising more and more interest from the low-vision research community since they offer a promising framework for low-vision aids and rehabilitation protocols. However, the study of VR accessibility to low vision is still in its early stages and designing efficient user interfaces for low-vision users remains an open challenge. Head pointing (a common way to interact with the world in VR environments) may represent a promising option for patients with Central Field Loss (CFL) who lose the ability to direct their gaze efficiently towards a target. Yet, little is known about the actual head-pointing capacities of CFL patients.Discussion: The purpose of the current study is to evaluate whether patients with CFL are able to perform precise head-pointing tasks in VR. 49 patients with binocular CFL, aged 34 to 97 (mean = 77±13), were tested with an Oculus Go headset in a very simple VR environment (grey background). At the beginning of each block, a head-contingent reticle was displayed in a specific location in front of the patient. A total of 9 reticle locations were tested either in the center of the visual field or with a 7° offset. At each trial, a target appeared in the visual field and patients were instructed to move their head to position the reticle precisely onto the target. Targets were black circles (1° to 3° diameter) randomly presented in five fixed positions (center or top, right, bottom, left at 18° of eccentricity). On average, patients were able to use their head to position the reticle precisely onto the target 94% of the time. Individual differences emerged, with a significant drop in pointing speed performance for specific reticle locations.Conclusions: Our preliminary results show that patients with CFL are able to perform accurately precise head-pointing tasks. This represents a fundamental step towards the design of efficient and user-friendly visual aids and rehabilitation tools using VR. For instance, head pointing could provide an ergonomic framework to design user interfaces that require precise pointing abilities to perform item selection. Similarly, one can imagine designing head-contingent pointing exercises that will drive the rehabilitation process while limiting straining of the eyes

Cortical and retinal responses analysis to retinal electric stimulation by subretinal implant on murine model

L’objectif de cette thèse est la validation fonctionnelle d’implants rétiniens pour la restauration fonctionnelle de la vision chez des patients non voyants suite à la perte de leurs photorécepteurs. Ce travail a été réalisé sur modèle animal et a évalué expérimentalement de nouveaux protocoles de stimulation. Tout d’abord nous avons utilisé la technique de spectroscopie d’impédance pour simuler mathématiquement l’interface tissu-implantafin de caractériser la présence d’un espace entre le tissu et l’implant. La seconde partie compare par imagerie optique (IO) les caractéristiques de la réponse corticale évoquée par stimulation visuelle ou électrique de la rétine par prothèse sous rétinienne. Nous avons retrouvé que la taille de l’activation par l’implant rétinien est beaucoup plus grande que son correspondant visuel. Dans une troisième partie, est réalisée une évaluation in vitro de la performance des stimulations sur rétine isolée pour définir comment les cellules ganglionnaires réagissent à différents modes de stimulations. Ce travail a permis d’établir la courbe des réponses en fonction de l’intensité des stimulations électriques. Enfin, la thèse décrit un modèle animal de dégénérescence rétinienne qui présente des désorganisations de la rétine externe. Une analyse en IO a été réalisée sur ce modèle afin d’évaluer la réponse corticale aux stimuli visuels et électriques. Ce travail de thèse, par des approches physiques et physiologiques complémentaires, apporte un certain nombre de réponses qui devraient permettre d’améliorer l’utilisation de futures prothèses rétiniennes par une adaptation physique des matrices d’électrodes ou des patrons de stimulations utiliséesThe aim of this thesis is the functional validation of retinal implants used for vision restoration in blind patients due to the loss of photoreceptors. This work was designed to develop an animal model to experimentally validate prototypes of new implants and new stimulation protocols pattern. Firstly we used the technique of impedance spectroscopy to simulate mathematically the tissue/implant interface. These data confirm the importance of reducing the space between the stimulating electrodes and retinal tissue, as well as the importance of physical characteristics of the electrical stimulus used. In a second approach, we have compared responses of visual cortical neuronal population using optical imaging (OI), evoked either by visual or electric retinal stimulation through subretinal prosthesis. This approach has demonstrated that the stimulation of an electrode induces cortical activation that the size of the cortical response to the retinal implant stimulation is much larger than its corresponding visual stimulus. In the third part, I performed in vitro experiment to measure the performance of stimulation at the level of ganglion cells of isolated retina. We have quantified the response curve as a function of the intensity of the electrical stimulation. Finally, the thesis describes a new animal model of outter retinal degeneration. OI was also performed on this model to assess the response to the visual and retinal prosthesis stimulations. This thesis, through complementary physical and physiological approaches, provides a number of responses that can potentially improve the use of retinal prostheses through specification of their design or patterns of stimulation

Un Modèle de néovascularisation cornéenne expérimentale chez le rat.

AIX-MARSEILLE2-BU Méd/Odontol. (130552103) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

Effects of multiple intravitreal anti-VEGF injections on retinal nerve fiber layer and intraocular pressure:a comparative clinical study

Letter to the edito

Inhibition of corneal neovascularization after alkali burn: comparison of different doses of bevacizumab in monotherapy or associated with dexamethasone

International audienc

Contribution of Short-Time Occlusion of the Amblyopic Eye to a Passive Dichoptic Video Treatment for Amblyopia beyond the Critical Period.

International audienceDichoptic movie viewing has been shown to significantly improve visual acuity in amblyopia in children. Moreover, short-term occlusion of the amblyopic eye can transiently increase its contribution to binocular fusion in adults. In this study, we first asked whether dichoptic movie viewing could improve the visual function of amblyopic subjects beyond the critical period. Secondly, we tested if this effect could be enhanced by short-term monocular occlusion of the amblyopic eye. 17 subjects presenting stable functional amblyopia participated in this study. 10 subjects followed 6 sessions of 1.5 hour of dichoptic movie viewing (nonpatched group), and 7 subjects, prior to each of these sessions, had to wear an occluding patch over the amblyopic eye for two hours (patched group). Best-corrected visual acuity, monocular contrast sensitivity, interocular balance, and stereoacuity were measured before and after the training. For the nonpatched group, mean amblyopic eye visual acuity significantly improved from 0.54 to 0.46 logMAR (p < 0.05). For the patched group, mean amblyopic eye visual acuity significantly improved from 0.62 to 0.43 logMAR (p < 0.05). Stereoacuity improved significantly when the data of both groups were combined. No significant improvement was observed for the other visual functions tested. Our training procedure combines modern video technologies and recent fundamental findings in human plasticity: (i) long-term plasticity induced by dichoptic movie viewing and (ii) short-term adaptation induced by temporary monocular occlusion. This passive dichoptic movie training approach is shown to significantly improve visual acuity of subjects beyond the critical period. The addition of a short-term monocular occlusion to the dichoptic training shows promising trends but was not significant for the sample size used here. The passive movie approach combined with interocular contrast balancing even over such a short period as 2 weeks has potential as a clinical therapy to treat amblyopia in older children and adults