Asymmetric Peripheral Refraction Profile in Myopes along the Horizontal Meridian

Abstract

SIGNIFICANCE:The investigation of peripheral refraction profiles in Indian myopes showed relative peripheral hyperopic refraction in temporal retina and possible dominant role of hyperopic defocus signals from temporal retina in the development of myopia. PURPOSE:Considering that the peripheral refraction profiles were extensively reported to be associated with the central refractive error and vary among different ethnicities, we investigated the peripheral refraction profiles in Indians.METHODS: A total of 161 participants aged between 18 and 33 years were included in the study. All of the eligible participants underwent a comprehensive eye examination. Central and peripheral refractions were determined using an open-field autorefractor in 10°intervals up to ±30°in the horizontal meridian, and in 5°intervals up to ±15°in the vertical meridian. Axial length and central corneal radius were measured using a non-contact optical biometer. Peripheral refraction was compared between the different refractive error groups and myopic subgroups.RESULTS: Myopes showed a significant asymmetrical peripheral refraction profile along horizontal meridian with relative peripheral myopia at nasal 30°and relative peripheral hyperopia at temporal 30°(mean ± standard error at N30°: −0.37 ± 0.13 D vs. T30°: +0.56 ± 0.11 D, P < .05). Emmetropes and hyperopes showed relative peripheral myopia both in nasal and temporal eccentricities. Relative peripheral refraction was significantly different between the refractive groups and myopic subgroups along the temporal retinal eccentricities only (P < .05). Along the vertical meridian, relative peripheral myopia was seen among the three refractive error groups (P < .05). J 0 and J 45 significantly changed with retinal eccentricity along both the meridians in all the refractive error groups (P < .05).CONCLUSIONS: Myopes showed an asymmetric type of peripheral refraction with relative hyperopic defocus in temporal retina and myopic defocus in the nasal retina. Possible role of retinal hyperopic defocus along temporal retina in myopiogenesis needs to be explored.

Association between relative peripheral refraction and corresponding electro‐retinal signals

“…Previous literature on peripheral refraction profiles reported RPH in myopes and RPM in hyperopes and emmetropes, with varying degrees of asymmetry across the horizontal and vertical meridians, especially in myopes 42–47 . We also found an asymmetry in the RPR profiles along the horizontal (RPM nasally and RPE temporally) and vertical (RPM superiorly and RPE inferiorly) meridians in myopes (Figure 2), which is consistent with another recent study by our group in Indian eyes 30 . These differences in the peripheral refraction profiles between myopes and non‐myopes and across the two meridians are mainly attributed to the natural variations in retinal shape and peripheral ocular biometry parameters that determine the peripheral refraction 2,30,33,48,49 …”

“…We also found an asymmetry in the RPR profiles along the horizontal (RPM nasally and RPE temporally) and vertical (RPM superiorly and RPE inferiorly) meridians in myopes (Figure 2), which is consistent with another recent study by our group in Indian eyes. 30 These differences in the peripheral refraction profiles between myopes and non-myopes and across the two meridians are mainly attributed to the natural variations in retinal shape and peripheral ocular biometry parameters that determine the peripheral refraction. 2,30,33,48,49 In the current study, the mfERG responses were maximum at the fovea in both non-myopes and myopes and largely declined with increasing retinal eccentricity.…”

“…30 These differences in the peripheral refraction profiles between myopes and non-myopes and across the two meridians are mainly attributed to the natural variations in retinal shape and peripheral ocular biometry parameters that determine the peripheral refraction. 2,30,33,48,49 In the current study, the mfERG responses were maximum at the fovea in both non-myopes and myopes and largely declined with increasing retinal eccentricity. The maximum mfERG responses at the fovea may be related to the highest cone photoreceptor density at the foveal region.…”

“…The central refraction was measured first followed by the peripheral refraction measurements in 5° steps up to ±30° horizontally and ±15° vertically. Measurements were recorded using the previously used standard protocol, 5,30–32 where participants fixated on the high‐contrast Maltese crosses placed as central and peripheral targets at the aforementioned eccentricities along the horizontal and vertical meridians in the participant's visual field at eye level on a flat wall located 3 m from the eye (Figure 1a) to minimise accommodation. For appropriate alignment of the autorefractor's optical axis with the line‐of‐sight of the participant's eye, the autorefractor was positioned such that the inbuilt fixation alignment red circle coincided with the central external fixation target before initiating the measurements 5,33 .…”

“…The central refraction was measured first followed by the peripheral refraction measurements in 5° steps up to ±30° horizontally and ±15° vertically. Measurements were recorded using the previously used standard protocol, 5,[30][31][32] where participants fixated on the high-contrast Maltese crosses placed as central and peripheral targets at the aforementioned eccentricities along the horizontal and vertical meridians in the participant's visual field at eye…”