Meridional Anisotropy of Foveal and Peripheral Resolution Acuity in Adults With Emmetropia, Myopia, and Astigmatism

Abstract

Purpose To quantify astigmatism-related meridional anisotropy in visual resolution at central, nasal, and inferior visual fields. Methods Three groups of young adults (range, 18–30 years) with corrected-to-normal visual acuity (logMAR 0) were recruited: (1) myopic astigmats (MA): spherical-equivalent error (SE) < −0.75D, with-the-rule astigmatism ≥ 2.00D, n = 19; (2) simple myopes (SM): SE < −0.75D, astigmatism ≤ 0.50D, n = 20; and (3) emmetropes (EM): SE ± 0.50D, astigmatism ≤ 0.50D, n = 14. Resolution acuity was measured for the horizontal and vertical gratings at central and peripheral visual fields (eccentricity: 15°) using a 3-down 1-up staircase paradigm. On- and off-axis refractive errors were corrected by ophthalmic lenses. Results The MA group exhibited meridional anisotropy preferring vertical gratings. At the central field, the MA group had better resolution acuity for vertical than horizontal gratings, and their resolution acuity for horizontal gratings was significantly worse than the SM and EM groups. At peripheral visual fields, both the SM and EM groups showed better resolution acuity for the radial (i.e., nasal field: horizontal gratings; inferior field: vertical gratings) than tangential orientation. However, the MA group tended to have better resolution acuity for the tangential orientation (i.e., vertical gratings), and their resolution acuity for horizontal gratings was significantly lower than the SM and EM groups at the nasal field. No significant differences were found in the inferior field among the three groups. Conclusions This study provided evidence of astigmatism-related meridional anisotropy at the fovea and nasal visual fields, underscoring the significant impact of astigmatism on orientation-dependent visual functions.

Agreement and Repeatability of Central and Peripheral Refraction by One Novel Multispectral-Based Refractor

“…Moreover, studies involving animal models have demonstrated that the peripheral retina refraction status dominated refractive changes whenever conflicts occur between the fovea and the peripheral visual signals ( 6 ). Therefore, this finding calls for the measurement of both the central and relative peripheral refractive errors with the overarching goal of elucidating the mechanisms of myopic development ( 7 ). It has been reported that inhibiting the progression of myopia by reducing the hyperopic defocus of the peripheral retina following a refractive correction is an effective method ( 8 ).…”

Meridional Attentional Asymmetries in Astigmatic Eyes

“…This confirmed the inversion of the horizontal-vertical foveal asymmetry found in myopic WTR astigmatism. 46 …”

“…This confirmed the inversion of the horizontal-vertical foveal asymmetry found in myopic WTR astigmatism. 46 RA: Horizontal and vertical also showed significant differences in resolution acuity in meridional difference (|V − H| = 6.703 ± 0.486, one sample t(8) = 13.794, p < 0.001), but, in contrast with RTs, the direction of fVHA varied among subjects. fVHA and Refractive Errors RA: When subjects attended target orientation, the vertical-horizontal asymmetry increased in line with the amount of defocus (Figure 3A, fVHA V congruent /H congruent Sph: r(9) = 0.711, p = 0.032; Cyl: r(9) = −0.253, p = 0.512), such that higher myopes had better vertical acuity than lower myopes.…”

“…Thus, in WTR myopic astigmats, it has been shown that there is significant superiority of acuity performance for isolated gratings along the vertical as compared to the horizontal (the horizontal effect). 46 Conversely, in emmetropes, the foveal vertical-horizontal asymmetry was found to be reversed and minimal, 46 leaving the well-known oblique effect 47 – an inferior performance for oblique orientation compared to cardinal (vertical/horizontal) orientation – as the predominant anisotropy observable for isolated gratings. While it appears that no studies have investigated the attentional origin of this neural retuning, anisotropic effects of attention have been previously demonstrated in peripheral vision 48–50 with a dominance of attention in the lower visual field as compared to the upper visual field 48 , 50 and in the vertical meridian as compared to the horizontal 49 for non-foveal stimuli.…”

“…Given the orientation dependence of astigmatic blur, 11,[42][43][44] such modulations could be realized through feature-based orientation. 45 In this respect, a possible neural retuning with refractive errors is indicated by the alterations of performance anisotropy in adult myopic astigmats, 46 as compared to adult myopes and emmetropes, under full optical correction. Thus, in WTR myopic astigmats, it has been shown that there is significant superiority of acuity performance for isolated gratings along the vertical as compared to the horizontal (the horizontal effect).…”