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[Setting the preferential retinal locus. Part 2. When, Where, and how does it become established?]
M Riss-Jayle1, R Giorgi, A Barthes
1Centre de rééducation basse vision, service d'ophtalmologie, CHU Timone, Marseille, France. martine.riss@ wanadoo.fr
Introduction:
The mechanisms underlying the localization of the preferred retinal locus (PRL) for visually impaired people has brought raised a number of hypotheses. In Part 1 we dissociated localizing the PRL from reading and writing tasks. Part 2 presents new hypotheses.
Material:
and methods: This study was conducted on 100 partially sighted people consulting at our low-vision rehabilitation center. The technique used compares angiofluorographies with images recorded with the scanning laser ophthalmoscope during fixation tasks. It localizes the PRL with respect to the fovea.
Results:
The PRL position was related to the size of the scotoma and the patient's visual damage. When there was only slight damage, the PRL was located on the left side or possibly in the superior position. When it worsened, the right position was significantly dominant; when it was severe, the PRL was generally located in the superior position or on the right. These positions were nearly always available for a given person.
Discussion:
The new visual message must be integrated into the most suitable cerebral locations for low spatial frequencies, damaged forms, messages transmitted by retinal rods, and finally global visual perception. It must favor the peri-personal space and near vision. These elements correspond to the new visual surroundings of the visually impaired. We believe that these data are better processed if they are transmitted by the lower and left visual fields. The rehabilitation program must take into account the above considerations. If the vision therapist orients the PRL location using eccentric view training or by having the patient wear a prism, he must keep in mind that the partially sighted's activities of daily life are the most important. At first, the superior side position, which leaves the field open to a maximum of visual tasks, must be trained, followed by the right position. Of course, when this localization has already been achieved, it must be respected.
