Effect of experimentally induced astigmatism on functional, conventional, and low-contrast visual acuity

Purpose: To report the changes in functional visual acuity (FVA) in eyes with experimentally induced astigmatism.

Methods: This study included 26 right eyes from 26 healthy participants (mean age: 27.0±4.4 years). After confirming best correction under cycloplegia, the cylinder power ×90° and ×180° (against-the-rule [ATR] and with-the-rule [WTR] astigmatism, respectively) were added with 0.50-diopter (D) steps, from 0.50 to 2.50 D. Conventional visual acuity (VA), FVA as measured by the FVA Measurement System (NIDEK Co Ltd), and 10% low-contrast visual acuity (LCVA) were measured with 3-mm artificial pupil under each condition.

Results: The mean corrected logMAR VA, FVA, LCVA were -0.18±0.00 (20/13), -0.10±0.08 (20/16), and 0.06±0.06 (20/23), respectively. The VA, FVA, and LCVA had a significant linear negative correlation with the addition of cylinder irrespective of the axes. A significant decrease in FVA was noted on addition of ⩾0.50 D WTR astigmatism and ⩾1.00 D ATR astigmatism. With the addition of 1.00 D of cylindrical lens, 96% of eyes with WTR and ATR astigmatism could maintain 20/20 in VA testing, whereas only 50% and 62% of eyes with WTR and ATR astigmatism, respectively, could maintain 20/20 in FVA testing.

Conclusions: Astigmatism may be associated with deterioration of visual function even when conventional VA of 20/20 is attained. Functional VA testing seems to be useful in evaluating the masked astigmatic visual impairment that cannot be detected by conventional VA testing.