Effects of residual astigmatism in contact lens wear on visual discomfort in VDT use.

The purpose of this study was to evaluate the effects of the residual astigmatism of contact lens wearers on the visual comfort of these individuals when using a video display terminal (VDT). We hypothesized that small amounts of uncorrected residual astigmatism of the type that is normally left uncorrected produce visual discomfort in the use of these devices even though visual acuity is relatively unaffected. Twelve subjects (ages 18 to 36 years) with corrected visual acuities of at least 20/25 (in each eye at distance with their contact lens correction) participated. All subjects were soft contact lens wearers who reported comfortable, well-adapted lens wear for a minimum of 1 year prior to the study. All subjects had between 0.50 and 1.00 D of residual astigmatism in each eye (mean = 0.68D). Our double-masked cross-over experiment included two 25-minute periods during which the subject read from a VDT. In a trial frame over their contact lens correction, the subjects were randomly assigned to wear either a test lens pair or a control lens pair (+0.12 DS) during the first period and the alternative pair during the second period. The test lens pair corrected all residual astigmatism (the over refraction). The control lens pair was considered a placebo. A questionnaire was used to obtain ratings of visual discomfort. Our analysis of the data indicated greater reported visual comfort for the test lens pair (Wilcoxon signed-rank test, p less than 0.01). These results suggest careful consideration be given to the correction of residual astigmatism of contact lens wearers who are VDT users.

Visual discomfort and astigmatic refractive errors in VDT use.

The purpose of this study was to evaluate the effects of small amounts of uncorrected astigmatism on the visual comfort of video display terminal (VDT) users. We hypothesized that these small errors produce visual discomfort in the use of these devices even though visual acuity is relatively unaffected. Eight subjects (ages 23-35 years) with corrected visual acuities of 20/20 participated. Our double-masked cross-over experiment included two 25-minute periods during which the subject read from a VDT. The subjects were randomly assigned to wear either the test lens pair (+0.50 D x 090) or a control lens pair (+0.12 DS) over their best correction during the first period and the alternative pair during the second period. A questionnaire was used to obtain ratings of visual discomfort. Our analysis of the data indicated greater reported eyestrain for the test lens pair (Wilcoxon signed-rank test, p = 0.01). These results suggest careful consideration be given to the correction of small amounts of astigmatic errors for VDT users.