Page 8 - Cahier-Pratical- Low-Vision-De-2014.indd

Visual Impairment 1. Glare 2. The Phenomenon of Completion Glare is a problem caused by excessive light. Certain pathologies We frequently observe a discrepancy between the results of create an extreme sensitivity to light and therefore cause photopho- tests aimed at measuring sight loss in an objective manner and the subjective view of the person suffering from the loss. This bia, i.e. the experience of ocular pain due to light. Figure 2 shows phenomenon is a physiological mechanism of cerebral plasticity how bright surroundings that would appear cheerful and sunny to most people are a source of visual discomfort to a visually impaired that consists in reconstituting a shape or flling up an area that is not actually seen in its entirety due to the objective scotoma. person, since their visual perception is considerably reduced by the blinding effect of the light. We should note that adapting to In the case of macular degeneration, for example, the perceived darkness is also generally long and diffcult; it takes time and, in central scotoma is often smaller than the extent of the macular lesion would lead us to believe. The information received by very many cases, causes discomfort. healthier retina adjacent to the macular lesion is given priority Figure 2: Importance of glare to a partially sighted person: by the cerebral cortex and this often allows the patient to hide the central blind spot completely or perceive a smaller “deleted area” than the original scotoma. This cortical plasticity is based on adaptive mechanisms and explains the successful development of compensation by rehabilitation. Practical Low Vision Subjective scotoma may be visualised with an Amsler grid, shown to the visually impaired person who is then asked whether the grid can be seen in full or whether one or more sections are missing. Figure 3: The Amsler grid: © Essilor International a) What a scene from daily life looks like to most people. © Essilor International This test may be carried out in either monocular or binocular vision. The former allows the assessment of the perceived scotoma for each eye and the latter enables assessment of the area of visual © Essilor International indicates any missing part of the grid and traces its contour. effciency. In both cases, the person fxates on the central point, b) Example of how it is seen by a partially sighted and photophobic person. 8 Copyright © 2013 ESSILOR ACADEMY EUROPE, 13 rue Moreau, 75012 Paris, France - All rights reserved – Do not copy or distribute. Copyright © 2013 ESSILOR ACADEMY EUROPE, 13 rue Moreau, 75012 Paris, France - All rights reserved – Do not copy or distribute.