Peripheral Refraction and Accommodation: What Causes the Change?

Abstract

Purpose: : There is much interest in the relationship between myopia development and peripheral refraction (PR). It has been postulated that hyperopic PR may be a driver of eye growth. While studies have anticipated a myopic-shift in PR on accommodation, the source of this shift is not well understood and may involve optical form changes in the eye and possibly changes in retinal position and shape. We studied the effect of accommodation on PR and attempted to isolate the contribution of optics of the eye from retinal shape changes.

Methods: : Twenty young subjects were enrolled to this study. Soft contact lens was used to correct refractive error throughout. Refraction was measured at 0°, 20°, 30° and 40° eccentricity both nasally and temporally using a Shin-Nippon autorefractor. All measurements were conducted at 2.5 m, 40 and 30 cm viewing distances. For some subjects, additional measurements were made at 21 cm.

Results: : PR becomes more hyperopic with eccentricity but less hyperopic on accommodation. Vertical astigmatism (J₁₈₀) increased with eccentricity and level of accommodation (0.50D-0.75D at 40°). Adopting 3^rd-order theory approximations, the Petzval surface dioptric position (PzP) relative to the retinal surface was estimated by considering the mean sphere (M) and J₁₈₀ terms of PR. Result shows that PzP relative to the retina changes only slightly on accommodation (<0.25D at 40°).

Keywords: myopia • refraction • accomodation