Light distortion of soft multifocal contact lenses with different pupil size and shape

Purpose: To study the light distortion effects of soft multifocal contact lenses and the influence of different pupil size and shape.Methods: A total of 14 eyes of 7 healthy contact lens users (mean age 28.6 +/- 8.5 years) were recruited. The "Light Disturbance Analyser" device was employed for light characterization. The selected lenses were the monthly disposable "Biofinity multifocal" (CooperVision, CA, USA), both centre-distance and centre-near designs (addition power + 2.50 D). Two circular pupils of 3 mm and 5 mm of diameter, and an elliptical shape (3 horizontal and 5 vertical mm) were used. Metrics such as the light distortion index (LDI), best-fit circle radius and its irregularity were analysed, among others.Results: The LDI was generally higher with multifocal lenses, varying from 3.7 +/- 0.3 % of the single vision lens to 6.1 +/- 3.3 % of the multifocal centre-distance design and the 5-mm pupil. Larger pupils gave higher LDI values, changing from 4.5 +/- 2.0 % (3 mm) to 6.1 +/- 3.3 % (5 mm) with the centre-distance design. The elliptical pupil produced the largest discrepancy in the distortion size between the vertical and horizontal directions. The centre-distance and centre-near designs behaved similarly in terms of light distortion.Conclusions: The multifocal contact lenses of the study increased light distortion effects under low light conditions, especially with larger pupils. The shape of the distortion pattern is associated with the shape of the pupil. It seems that not all, but a big percentage of light distortion would be produced by the presence of the out-offocus images given by a multifocal lens.This research was supported in part by a "Formacion de Profesorado Universitario" Grant (FPU13/05332, Ministerio de Educacion, Cultura y Deporte) awarded to Daniel Monsalvez-Romin, and by the research project GV/2015/043, from "Conselleria d'Educacio, Investigacio, Cultura i Esport de la Generalitat Valenciana", awarded to Alejandro Cervino. Work performed at University of Minho has been partially supported by projects PTDC/SAU-BEB/098391/2008, PTDC/FIS-OPT/0677/2014 and UID/FIS/04650/2019