Objective Measure of Halo Size With Multifocal Contact Lenses

Abstract

Abstract: : Purpose:We have developed a test to measure halos. This study examined the effects of spherical defocus on measured halo size and determined the diameter of halos perceived during multifocal contact lenses wear. Methods:Ten spectacle and 24 presbyopic contact lenses wearers were used in the optical defocus and multifocal lens experiments, respectively. Halos were simulated by having the subjects view a 10 mm diameter luminous aperture against a black background from 3 meters under scotopic condition. The size of halo was scaled relative to the size of the center light and judged using a faint grid visible on the dark background. The drawn halos were digitized. In the defocus session, halo sizes were measured monocularly with best sphere-cylindrical correction and with 0.25D step of defocus up to 1 D. Ultravue 2000 multifocal contact lenses were used in the multifocal lens session as there are different optical characteristics of the distance and near lenses in the dominant and non dominant eyes. Lenses were fit according to manufacturer's guidelines. Optimal powers for both distance and near vision were obtained before lenses were dispensed. Measurement of halo size was done monocularly and binocularly after 2 weeks of lens wear. Subjects also rated how frequently they were disturbed by halos around lights using analogue scales. Results:A significant association between the amount of optical defocus and increase in halo size was found (r=0.99, p=0.00) in the defocus session. Perceived halo size was different in distance and near eyes (Repeated Measure ANOVA p=0.00). Halo sizes measured monocularly with distance eye viewing and binocularly were significantly smaller than that with the near eye viewing (Tukey HSD all p=0.00). The difference in halo sizes between distance and near eye was not correlated to the power difference between distance and near focus in multifocal lens wearers (r=0.32, p=0.13). The measured halo size was not associated with the frequency of self-reported disturbance by halos around lights (r=-0.03, p=0.90). Conclusions:We demonstrated the validity of a simple test in which the perceived halo size could be calculated. Halo size varied linearly with dioptric defocus. The halos perceived during multifocal lens wear appeared not to be solely accounted for by optical defocus.

Keywords: contact lens • cornea: clinical science