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Comparison of Suppression, Stereoacuity, and Interocular Differences in Visual Acuity in Monovision and Acuvue Bifocal Contact Lenses

Optometry and Vision Science: December 1999
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Purpose: The relationship between visual acuity and stereoacuity has been well documented: as binocular visual acuity increases, stereoacuity improves. We compared interocular differences in visual acuity and stereoacuity in two presbyopic soft contact lens modalities, monovision and a new soft bifocal contact lens, the Acuvue Bifocal. The Acuvue Bifocal is hypothesized to show a smaller interocular acuity difference, increased stereoacuity, and decreased suppression over monovision at distance and near. Methods: Monovision patients wearing Acuvue or Surevue soft contact lenses were tested for visual acuity, stereoacuity, and suppression at distance and near. Stereoacuity was tested with the Randot Stereotest (near) and the BVAT (distance). Suppression was evaluated with the Acuity Suppression Vectogram (near) and the BVAT (distance). Patients were then fit with the Acuvue Bifocal in each eye. After wearing the lenses for 1 week, the same tests of visual acuity, stereoacuity, and suppression were performed. Results: The mean interocular acuity difference (IAD) at distance with monovision was 0.712 logarithm of the minimum angle of resolution (logMAR) (SD=0.275) and 0.188 logMAR (SD=0.252) (p<0.001) with the Acuvue Bifocal. At near, the mean IAD with monovision was 0.420 logMAR (SD=0.183) and 0.137 logMAR (SD=0.147) (p<0.001) with the Acuvue Bifocal. Of the monovision subjects, 89% (17 of 19) demonstrated suppression at near while only 26% (5 of 19) did with the bifocal lenses (statistically significant at p<0.001). Stereoacuity at near improved from a median of 200 sec arc with monovision to 50 sec arc with the bifocal lenses. Conclusions: In this study, correcting presbyopia with the Acuvue Bifocal versus monovision resulted in a statistically significant decrease in the interocular difference in visual acuity at distance and near. The decreased interocular difference in visual acuity improved certain aspects of binocularity as demonstrated by a decrease in suppression and an increase in stereoacuity.

© 1999 American Academy of Optometry