The impact of soft contact lens dynamic movement, patient ocular spherical aberration distribution and clinical refraction error on lens visual correction performance

Abstract

Purpose : Spherical aberration (SPHA) presenting in both soft contact lenses and a wearer's eyes affect visual acuity (VA) by blurring retinal images. Ocular SPHA varies across individuals depending on various factors including accommodation, age, pupil size and spherical refraction. For a contact lens wearer, the two optical systems might not be aligned since the lens moves dynamically on the eye. In addition to the opto-mechanical aspects, in clinical practice, refraction errors also occur. In this study, simulations were conducted to quantitatively investigate these effects.

Methods : Ocular SPHA distribution was obtained based on clinical measurements and a lens was designed with varying SPHA depending on refraction power. Area modulation transfer function (AMTF) based VA (using as the metric) was calculated to quantitatively evaluate the visual correction performance of the lens design. To account for a lens dynamically moving, a 300 µm standard deviation of lens dynamic movement was assumed. A 0.50D standard deviation was employed as the clinical refraction error. Simulations were conducted based on 100 eyes at 3, 4 and 6 mm pupil size and VA at distance, intermediate and near were calculated.

Results : The interaction of SPHA between lens and eye was shown to affect lens visual correction performance significantly in the accommodation process. With a 6-mm pupil size, on average for contact lens with +0.16 D/mm² SPHA, from distance vision (infinity distance) to near vision (2.0D), VA improves from -1.7 to -0.6. While for a contact lens with -0.08 D/mm² SPHA, the VA does not vary significantly. For a lens with -0.17 D/mm² SPHA, from distance to near vision, the VA deteriorates from -1 to -1.4. Simulations also indicate that the biggest VA degradation of 1.4 was observed with a lens with -0.08 D/mm² SPHA at distance due to lens movement, refractive error and patient SPHA distribution.

Conclusions : In general, the lens visual correction performance degrades due to lens movement, ocular SPHA distribution, and clinical refractive error. Interactions between the wearer ocular SPHA and the lens SPHA also have a significant impact on lens vision correction performance especially at distance vision for lens with higher positive SPHA, and near vision for lens with stronger negative SPHA.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.