Abstract
Purpose :
Retinal image blur in the periphery varies remarkably between individuals and their refractive state. Furthermore, the sign and shape of peripheral blur may provide a cue for the sign of defocus, and hence may play a role in accommodation and emmetropization. This study sought to investigate the peripheral image quality through-focus and how it depends on the eye’s refractive error.
Methods :
Previously published [1] Zernike coefficients across retinal eccentricity (0, 10, 20 and 30 deg horizontal visual field) were used to compute the monochromatic modulation transfer function (MTF) at 555 nm for a 4 mm pupil. Two-dimensional MTF was computed through-focus, from -3 to +3 D in 0.1 D steps at each eccentricity and used to define two metrics of image quality: (1) overall image quality defined as the volume under the MTF (vMTF) and (2) blur anisotropy defined as the ratio of the horizontal to vertical meridians of the MTF (HVRatio).
[1] Romashchenko, D, R. Rosén, and L. Lundström. "Peripheral refraction and higher order aberrations." Clinical and Experimental Optometry 103.1 (2020): 86-94.
Results :
Across the horizontal visual field (at 10, 20, 30 deg), through-focus vMTF revealed best focus (max vMTF) close to the retina in emmetropes (-0.3, -0.3, 0.0 D, respectively), as opposed to myopes whose best focus was behind the retina (-0.1, 0.4, 1.5 D, respectively) and hyperopes in front of the retina (-0.5, -0.6, -0.6 D). At 0.0 D (on the retina), emmetropes and hyperopes both exhibited radially elongated blur, whereas myopes had circumferentially elongated blur (HVRatio = 0.3, 0.7 and 2.8, respectively, at 30 deg eccentricity). In all groups, peak vMTF (best focus) coincided with radially elongated blur.
Conclusions :
Blur in the peripheral retina is dominated by so-called “odd-error” blur signals, primarily due to oblique astigmatism. Thus orientation of peripheral blur (radial vs circumferential) provides the eye with an optical cue for the sign of defocus and may play a role in mechanisms of accommodation and emmetropization. All subject groups had anisotropic blur in the periphery: myopes exhibited a circumferentially elongated peripheral blur, whereas emmetropes and hyperopes exhibited radial blur. These differences may be due to the interaction between peripheral wavefront aberrations and field dependent axial length (i.e. globe shape).
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.