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Fan Yi, Michael J Collins, Brett A Davis; Optical adaptation to spherical aberration. Invest. Ophthalmol. Vis. Sci. 2019;60(9):597.
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© ARVO (1962-2015); The Authors (2016-present)
It is known that the human eye can adapt to optical aberrations over time and improve its visual performance. This adaptation is generally believed to be neural in origin. In this experiment we examined the eye’s optical response to induced longitudinal spherical aberration (LSA) by measuring the wavefront of the eye over 40 minutes, followed by 15 minutes clear vision.
Six young adults (26 ± 7 yrs) participated in the experiment. Testing was conducted of three conditions on three separate days in a randomized order. Participants monocularly viewed a movie on a TV monitor through an adaptive optics system, where the refractive error of the eye was either: (1) optimally corrected with best sphero-cylinder, or (2 and 3) optimally corrected with an additional + 2 D or -2 D of LSA for a 5 mm pupil. After 20 mins “washout” with optimal correction, one of the three optical conditions was introduced and measurements of the eye’s wavefront were taken every 10 mins, till at 40 mins an optimal correction was reintroduced and the TV was viewed for a further 15 mins (“recovery”).
Repeated measures analysis of variance showed a significant interaction between the blur condition and time (p<0.01). In response to viewing through positive LSA, the wavefront of the eye showed a shift towards negative LSA (change -0.23 ± 0.17 D, p=0.011). After viewing through negative LSA, a positive change of + 0.13 ± 0.06 D LSA was measured (p=0.105). The control condition with optimal correction showed no significant changes in the eyes LSA over 40 mins. In the subsequent 15 min period of clear vision, the LSA of the eye showed regression to near baseline values after both the positive and negative LSA viewing conditions. The natural change in LSA of the eye with accommodation did not contribute to the result and there was no drift of the AO system LSA over time when measured with a model eye.
This small but systematic shift in the LSA of the eye could be the result of adaptive changes in the optics of the eye (eg. crystalline lens) or more likely, be the result of changes in the direction of light emerging from photoreceptors at the fovea. We estimate that the wavefront sensor beam created a spot size of about 50 microns centered at the foveola. A small active reorientation of the photoreceptor direction could account for these observations.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
Figure 1. Change of LSA of the eye in a 5 mm pupil over time.
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