Visual Acuity and “Balanced Progressive” Simultaneous Vision Multifocal Contact Lenses

Objectives. To investigate how add power affects binocular distance visual acuity in subjects wearing simultaneous vision, balanced progressive, multifocal contact lenses. Methods. Twenty-five young normally sighted subjects were fit binocularly, according to the manufacturers’ fitting nomogram, with CooperVision Proclear Multifocal contact lenses. A multifactorial experimental design was used to study distance visual acuity measured to the single letter with repeated measures on add power (+1.00, +1.50, +2.00, +2.50), light level (photopic and mesopic), and Bailey-Lovie chart contrast (high and low). Results. The relationship between add power and visual acuity was analyzed by linear regression for each of the 4 test conditions. The corresponding mean decrease in equivalent Snellen visual acuity from 20/16 to 20/17 between the +1.00 and +2.50 add powers for the photopic light level, high contrast test condition was not significant (F = 3.068, P=0.083). However, the change in visual acuity from 20/24 to 20/27 between the same add powers for the low contrast, photopic test condition was significant (P=0.048), as was the loss in visual acuity from 20/24 to 20/28 for the high contrast, mesopic test condition (P=0.005) and the reduction from 20/45 to 20/61 for the low contrast, mesopic light level test condition (P=1.5 × 10−5). Pupil diameter averaged 3.9 ± 0.07 mm and 6.2 ± 0.12 mm under photopic and mesopic light levels, respectively. Conclusions. Distance visual acuity averaged better than 20/20 for all add powers under high contrast, high illumination test conditions and decreased by a small, but significant amount, under other testing conditions.