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 x 10). 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.