When fit with monovision, most early presbyopes (aged 40 to 50 years) accommodated to near objects by focusing the distance corrected eye, leaving the near corrected eye myopically defocused with reduced image quality. A few were able to switch focus to the near corrected eye retaining a consistently focused image in one eye over a wider range of distances.
The aim of this study was to examine accommodation behavior, pupil responses, and resultant image quality of early presbyopes fit with either bilateral or unilateral (monovision) near adds.
Accommodative response and pupil size of 19 subjects (27 to 60 years), including 13 early presbyopes (40 to 50 years), were measured using an aberrometer as a binocularly viewed 20/40 letter E was moved from 2 m to 20 cm. Each subject was fit with different refractive strategies: bilateral distance correction, bilateral +2 diopters (D) near add, and unilateral +2 D near add placed over the measured right eye or unmeasured left eye. Monochromatic image quality was quantified using the Visual Strehl ratio metric.
With bilateral +2 D near add, all early presbyopes mostly refrained from accommodating (gain = 0.22 D/D) until the target approached closer than the 50-cm far point, and they then accommodated accurately until their maximum accommodative amplitude was reached. With monovision, most (10 of 13 early presbyopes) accommodated to focus the distance corrected eye, leaving the near corrected eye myopically defocused with reduced image quality. As stimulus distance became closer than their distance corrected eye's near point, they continued to exert maximum accommodation. Only two early presbyopes relaxed their accommodation to “switch” focus to the near corrected eye as target distance was reduced, and these two did not experience bilateral drop in image quality as stimulus distance became closer than the near point of the distance corrected eye.
Our data suggest that many early presbyopes will not initially adopt an accommodation strategy that optimizes image quality with monovision, but consistently accommodate to focus the distance corrected eye.
1School of Optometry, Indiana University, Bloomington, Indiana
2Department of Optometry, College of Applied Medical Sciences, King Saud University, Riyadh, Saudi Arabia *email@example.com
Submitted: November 28, 2016
Accepted: September 11, 2017
Funding/Support: None of the authors have reported funding/support.
Conflict of Interest Disclosure: None of the authors have reported a conflict of interest.
Author Contributions and Acknowledgments: Conceptualization: MSA, AB; Data Curation: MSA; Formal Analysis: MSA, BHA, AB; Methodology: MSA, BHA, AB; Project Administration: MSA; Writing – Original Draft: MSA, AB; Writing – Review & Editing: MSA, AB. Some of the data were presented at two meetings: the American Academy of Optometry Annual Meeting, October 2015, New Orleans, Louisiana, and at the Association for Research in Vision and Ophthalmology Meeting, May 2016, Seattle, Washington.