Influence of ophthalmic lenses in the illuminance originated at a peripheral glare source and reaching the eye

Abstract

To study the influence of glare on the visual performance of a subject wearing an ophthalmic lens, it is useful to know how the lens affects the illuminance reaching the eye. In this paper, considering spherical standard ophthalmic lenses and defining the relative illuminance, Er, as the quotient between the illuminance at the cornea with and without lens, a methodology to evaluate Er in terms of easily determined parameters is developed. Three effects are considered, pupil size variation of the system with and without lens; lateral shifts of rays transmitted through the lens and reflections at the lens. Calculations are experimentally verified employing 5 organic ophthalmic lenses of ±6; ±4 and 0.12 dioptres and 2 glass plane parallel plates 1.95 and 6.6 mm thick. Using a photometer whose sensor is 12 mm apart from the lens and 740 mm apart from a glare source subtending an eccentricity angle of 9.6°, it results Er=1.204 for the 6 dioptres lens and Er=0.803 for the -6 dioptres one if sensor diameter is 10 mm while, for a 719 mm distance and a 10° angle, Er=0.922 for the thin plate and a 30 mm sensor and Er=1.006 for the thick plate and a 10 mm sensor. Experimental and theoretical results differ in less than 3%.