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Zone of Clear Single Binocular Vision in Myopic Orthokeratology

Gifford, Kate L. Ph.D.; Gifford, Paul Ph.D.; Hendicott, Peter L. Ph.D.; Schmid, Katrina L. Ph.D.

doi: 10.1097/ICL.0000000000000614
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Purpose: To examine the zone of clear single binocular vision (ZCSBV) in myopic children and young adults after 12 months of orthokeratology (OK) wear, in comparison with single-vision soft contact lens (SCL) wear.

Methods: Twelve children (8–16 years) and 8 adults (18–29 years) were assessed with a series of near-point binocular vision tests when myopia was corrected using single-vision SCLs and again after 1 and 12 months of OK wear, and axial length was measured. The ZCSBV was constructed for baseline SCL wear and after 12 months of OK wear.

Results: After 1 month of OK wear, increased accommodative responses were noted in children (C) and adults (A) as increased binocular amplitude (C:P=0.03, A:P=0.04) and reduced accommodative lag (C:P=0.01, A:P=0.01). Divergence reserves improved after 1 month in both groups (P<0.04), and a near exophoric shift was evident at 12 months (C:P=0.01, A:P=0.04). All changes at 1 month maintained stability at 12 months. An increase in accommodation and vergence responses without reduction in range resulted in an expansion of the ZCSBV in both age groups. Axial length did not significantly change in either children (P=0.25) or adults (P=0.72).

Conclusion: In both pediatric and young adult myopes, the ZCSBV expands toward a more divergent, increased accommodation response in OK compared with SCL wear. This occurs without a corresponding loss of convergence or accommodation deactivation, indicating improved depth of focus. These findings are relevant to visual acceptance and possible mechanisms of OK's efficacy for myopia control.

School of Optometry and Vision Science (K.G., P.L.H., K.L.S.), Faculty of Health, Institute of Health and Biomedical Innovation, Queensland University of Technology, Queensland, Australia; and School of Optometry and Vision Science (P.G.), Faculty of Science, University of New South Wales, New South Wales, Australia.

Address correspondence to Kate L. Gifford, Ph.D., School of Optometry and Vision Science, Faculty of Health, Institute of Health and Biomedical Innovation, Queensland University of Technology, 60 Musk Avenue, Kelvin Grove, Queensland 4059, Australia; e-mail: kate@gjo.com.au

The authors have no funding or conflicts of interest to disclose.

Accepted March 11, 2019

© 2019 Contact Lens Association of Ophthalmologists, Inc.