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LOWVISION - Processus perceptifs et cognitifs après perte partielle ou totale de la vision maculaire : vers une approche plus écologique

Project Coordinator : LNFP Lille
Project Manager at GIPSA-lab : Nathalie GUYADER

Project realized thanks to the support of : ANR Blanc

Start date : 2011/12/08

Duration : 48 mounths


 

The number of pathologies related to age is in constant progression in western countries. Notably, age related macular degeneration (AMD), inducing a central vision loss, affects about 1 million people in France. AMD is a pathology that gradually reduces sight without warning as its progression is slow and painless (in its common form, see below). Because macular degeneration usually begins slowly and asymmetrically on the two eyes, many people do not immediately realize that they are progressively losing their sight.
There are two types of macular degeneration: wet (neovascular or exudative) and dry (atrophic). The dry form is the most common type, accounting for as much as 90 percent of all cases. Both wet and dry macular degeneration have similar symptoms. Wet macular degeneration can be treated with medication, laser eye surgery, or photodynamic therapy to stop further formation of abnormal blood vessels in the retina. However, the treatment cannot reverse damage that has already occurred. Dry macular degeneration is currently untreatable. AMD is an invalidating pathology that affects social life and induces a loss of autonomy.
AMD affects the region of the retina with the highest density of receptors: the macula, about 6 mm in diameter, covering the central 15-20° of the visual field. As the macula is responsible for high spatial resolution, the patients‟ ability to obtain information about the environment is reduced to peripheral vision, which is characterized by low spatial resolution (the density of receptors decreases with eccentricity). These people report increased difficulties for everyday tasks like reading, driving, cooking, watching TV, recognizing faces and facial expressions, recognizing pictures and finding objects especially when the illumination level is low (Hart et al., 1999; Brody et al., 2001; Holzschuch et al 2002; Hassan et al., 2002; , Rubin et al. 2001; Rubin et al. 1994a; Tejeira et al., 2002; Boucart et al 2008a).
Vision-related Quality of Life questionnaires (Mangione et al 2001; Cahill et al 2005) report that patients suffering from AMD also encounter more difficulties than do age matched normally sighted individuals when shopping (i.e., finding objects on shelves), managing money, preparing meals and performing light housework. Hence, AMD has consequences for social life as these people progressively lose their autonomy. Patients are impaired at finding objects at home and in shops, for driving and using public transportation (being unable to read the directions in the subway or buses), for communication as recognition of facial expression and eye direction represent an important way of communication (Peterson & Rhodes 2003; Itier & Batty 2009 for reviews).
Eye-related aging diseases also have medical and economical impacts. Indeed, as compared to age-matched normally sighted people, many of these people must live in institutions, the risk of fall injuries is two times higher than in age-matched normally sighted people, the number of hip lesions is multiplied by four and the incidence of depression is three times higher than in age-matched normally sighted people. For instance, in the northwest part of France the socio-economical cost of patients with low vision, including ophthalmology, rehabilitation and psychology, is evaluated at about 4000 Euro/month per individual. This cost does not take into account optical devices and glasses.
All of this indicates that there is a need to characterize the specific capabilities, and inabilities, associated with central visual field loss and a need to understand the normal capabilities of peripheral vision for object and scene recognition and for spatial memory.
Indeed, understanding the visual processes impaired, and those spared, is critical (Rubin, 2001) :
- for efficient visual and motor re-habilitation,
- for the development of efficient optical systems taking into account the physiological and cognitive properties of the visual system,
- for adapting the physical environment in which these patients live and interact and, therefore, - for maintaining a relative autonomy in these people notably by improving their reading performance, which is a crucial cognitive function in our societies where written information and images is ubiquitous.

The mechanims of the perceptual and cognitive impairments in AMD patients are still poorly understood in two important domains. First, very little is known about the capabilities of residual vision in the far periphery, and especially above 30° eccentricity as, mainly for technical reasons (the size of computer screens), the majority of the studies on peripheral vision in normally sighted people have been performed below 20°. Secondly, the impact of Central Field Loss (CFL) on the specific processes involved in active vision (i.e., when people move their eyes, head and body) remains very unclear or under-investigated.


Our research program will therefore be organized along two complementary lines of research:
(1) Residual vision in the far periphery: these studies involve basic research. They will focus on the perceptual and cognitive aspects of the visual impairments encountered by people with low vision consecutive to macular degeneration, and particularly on visual object and scene perception in peripheral vision and in spatial memory representations in the far periphery and in central vision (in patients with relative scotoma).
(2) Specific characteristics of Active vision with Central Field Loss Active vision concerns the visual functions that necessitate moving the eyes, head and/or body in order to extract relevant visual information. Reading, which implies a series of gaze fixations along a line of text, is a famous example of active vision. The working hypothesis of this axis of research is that many functional impairments in people with central vision loss result from disorders in active vision.


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