Defocus vibrations improve visual resolution of defocused targets

Abstract

Purpose : To test the hypothesis that rapid step changes in defocus for an out-of-focus retinal image increase visual resolution.

Methods : Visual acuity (VA) of 5 subjects (37 ± 12 y.o.) was measured under monocular conditions with a Freiburg VA test using a microdisplay that showed a high-contrast black Landolt-C letter on a white background. The text was presented at the subject’s far point or 1.00 D beyond it. VA was also measured when the target was at 1.00 D beyond the far point and longitudinal vibrations in defocus were added with different amplitudes. The longitudinal vibrations were generated as step changes at 50 Hz with a deformable mirror in a custom adaptive optics system (MurciAO) and with amplitudes of 0.25, 0.50, 0.75, and 1.00 D. In all trials, the Freiburg VA test was performed using a microdisplay that was seen through a 4-mm artificial pupil. Five repeated measurements were obtained under each viewing condition.

Results : VA of the defocused target improved as the tested amplitude of vibrations increased. Figure shows an example of the object photographed through the optical system by a camera with an exposure time of 1/6 s. Mean logMAR was −0.14 ± 0.07 at the far point, 0.35 ± 0.16 at 1 D beyond the far point and in between these two values when defocus vibrations were generated. More precisely, mean logMAR values were 0.26, 0.22, 0.10, and 0.02 for defocus vibrations with amplitudes of 0.25, 0.50, 0.75 and 1.00 D, respectively. Linear regression analysis showed a negative statistically significant (R² = 0.59 ± 0.17, all p < 0.01) slope of VA with respect to the amplitude of vibrations that ranged between −0.16 and −0.41 logMAR units per D of amplitude.

Conclusions : Visual resolution of defocused targets improves with defocus vibrations. Our study confirms that the theoretical result predicted by Lohmann and Paris (App. Opt. 1965) is applicable to the human eye. The results add more insight into the role of wavefront dynamics in the human eye.

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

 

Figure. Landolt C eye chart seen through the system in focus (left), with 1 D of defocus (middle), and with 1 D of defocus with vibrations of 1 D of amplitude.