Can Tinted Lenses Be Used to Manipulate Pupil Size and Visual Performance When Wearing Multifocal Contact Lenses?

ABSTRACT

BACKGROUND: The purpose of this study is to investigate the effect of wearing neutral density (ND) filters with different transmittance levels over multifocal contact lenses (MTF CLs) on pupil size, visual functions and the dynamic accommodative response under daylight conditions in early presbyopes. METHODS: Seventeen individuals aged between 40 and 48 years (mean age 42.35±2.62 years) were recruited to participate in this study. This study involved a repeated-measures design with two within-subject factors optical condition (which had five levels), and fixation distance (which had three levels). The five optical conditions were no correction (baseline), MTF CL wear, MTF CL wear + 0.3 ND filter (transmission [Tv]=48.38%), MTF CL wear + 0.6 ND filter (Tv=27.12%) and MTF CL wear + 0.9 ND filter (Tv=14.58%). The three fixation distances were 3 m, 40 cm and 20 cm. Outcome measures were pupil size, the measured accommodative response (optical aid + physiological accommodation), distance visual acuity (VA), near VA and contrast sensitivity (CS). RESULTS: There was no effect of optical condition on the accommodative response; however, there was a significant effect of fixation distance. (Accommodative response was 0.44±0.29, 1.83±0.37 and 4.03±0.46 D for fixation distances of 3 m, 40 cm and 20 cm, respectively; p<0.05.) There was a significant effect of optical condition (p<0.05) and of fixation distance on pupil size variation (5.13±0.90 mm for 3 m, 4.71±0.92 mm for 40 cm and 4.11±1.04 mm for 20 cm; p<0.05). Optical condition had a significant effect on distance VA, near VA and CS (p<0.05). Compared to the reduction in distance VA, near VA was relatively small (two-letter reduction with 0.9 ND) and unlikely to be clinically significant. CONCLUSION: This study demonstrated that in a group of adults with early presbyopia, the use of ND filters enlarged pupil size. However, the combination of enlarged pupils and MTF CL did not improve distance vision, and if transmittance was reduced by 50% it resulted in decrements in vision and CS. MTF CL designs which incorporate tints, or tints that vary in darkness in response to ultraviolet exposure, should consider these findings.