Influence of ophthalmic lenses in the angle subtended by a peripheral source point

摘要

When a myopic or hyperopic eye wearing an ophthalmic lens looks at a stimulus and also receives light from a peripheral point, the lens modifies the eccentricity angle with which light originated at this point reaches the eye. Under paraxial approximation, the lens visual magnification (quotient between the angles subtended at the corneal vertex by the point and by its image through the lens) can be evaluated as usual, either considering thick or thin lens. In the first case, the calculation requires data (not always available) concerning source location, lens construction parameters and vertex distance while, in the second, results are imprecise for thick lenses employed by patients suffering severe hyperopia. To avoid these drawbacks, in the present article we obtain a formula for the mean visual magnification of a standard ophthalmic lens of spherical surfaces as a function only of its power. We propose the use of this formula to estimate in a simple and approximate way the effective eccentricity angle corresponding to a far or near point source and to any standard ophthalmic lens and habitual vertex distance.