Page 11 - Cahier-Progressive Lenses-GB.indd

Physiology C Binocular vision Binocular vision includes simultaneous perception, Sensorial fusion: fusion of the images and the stereoscopic sense. With a To ensure sensorial fusion the retinal images formed in progressive lens the criterion for good binocular vision is each eye must be similar in all directions of gaze. To that 2 to enable natural fusion and perception by the two eyes. end, the power and astigmatism encountered in cor- responding areas of the right and left lenses must be Motor fusion: approximately equal, for all directions of gaze. The The eyes naturally converge when the gaze is lowered for concept of asymmetry of the progressive surface is for near vision. The power progression must be positioned that purpose very important: the lens should be desi- on the lens in order to follow the eye’s path of conver- gned with a symmetry along horizontal lines, on each Progressive lenses gence downwards in the nasal direction. For ease of side of the oblique line of power progression, so as to motor fusion, in all directions of gaze both right and left keep approximately the same image for each eye during lenses must exert approximately equal vertical prismatic lateral rotation of the eyes around the intermediate and effects on each side of the power progression path. near fields. Fig. 8 : Binocular vision with progressive lenses. The physiological criteria for progressive lenses can be defined using two different approaches: - either by considering the average visual requirements of a large number of presbyopes in order to achieve a “universal” progressive design, - or by attempting to highlight specific needs of the wearer in order to achieve a “personalized” design. These opposite but complementary approaches are the origin of the two major categories of progressive designs which are available today, progressives for “universal use” and “personalized” progressives. 11 Copyright © 2006 ESSILOR ACADEMY EUROPE, 13 rue Moreau, 75012 Paris, France - All rights reserved – Do not copy or distribute.