Global‐flash mfERG responses to local differences in spherical and astigmatic defocus across the human retina

Abstract

Purpose Emmetropisation is essentially a visually guided, within‐eye process. We investigated differences in global‐flash multifocal electroretinogram (gmfERG) responses to naturally occurring differences in spherical and astigmatic defocus across the retina, which might provide a basis for guiding eye growth. Methods Experiment 1: The gmfERG responses (direct, DC, and induced, IC, amplitudes and latencies) recorded simultaneously from six retinal areas (15° eccentricity, spaced at 60°, areas 3.2°2) were correlated with the uncorrected retinal defocus measured at the six corresponding retinal locations in 20 adults with foveal refractive errors (−4.75 to +1.25D). No correcting lenses were used to avoid introduction of lens‐induced aberrations and magnification. Experiment 2 investigated the effect of superimposing astigmatic defocus (+2.00/−4.00D Jackson Cross Cylinder presented at four orientations) on gmfERG responses. Results Experiment 1: DC and IC response amplitudes were greater in retinal regions naturally exposed to more hyperopic spherical defocus (DC: rho = 0.26, p = 0.005; IC: rho = 0.29, p = 0.001), but response latencies were unaffected by sign or magnitude of spherical defocus (DC: p = 0.34; IC: p = 0.40). Response amplitudes and latencies were unaffected by astigmatic defocus. Experiment 2: Rotating the JCC axis to four different orientations had no effect on the gmfERG responses (DC amplitude, p = 0.39; DC latency, p = 0.10; IC amplitude, p = 0.51; IC latency, p = 0.64). Conclusion The gmfERG responses from discrete retinal areas varied with the sign and magnitude of local spherical defocus, but we found no evidence that retinal responses were affected by astigmatic defocus. Therefore, local astigmatism is unlikely to provide cues for controlling eye growth, whereas differences in response to spherical defocus between different retinal regions could potentially provide cues for controlling eye growth in emmetropisation.

The effect of simultaneous dual‐focus integration on the global flash multifocal electroretinogram in the human eye

“…Finally, the DFCL used in the current study would create two image shells (i.e., in-focus and myopic defocus) on the retina. It is possible that this triggers an integrated activity due to the two focal shells, which differs from the uncorrected defocus in Turnbull et al 32 There are several limitations in the current study. The actual retinal defocus in the three regions experienced by the individuals was not measured.…”

“…Finally, the DFCL used in the current study would create two image shells (i.e., in‐focus and myopic defocus) on the retina. It is possible that this triggers an integrated activity due to the two focal shells, which differs from the uncorrected defocus in Turnbull et al 32 …”

“…A recent study by Turnbull et al 32 investigated the relationship between uncorrected peripheral refractive error and global flash mfERG. Although the peak time was consistent, their findings on the DC and IC amplitudes appeared to differ from the results of the current study.…”

“…A recent study by Turnbull et al 32 . investigated the relationship between uncorrected peripheral refractive error and global flash mfERG.…”

Exogenous Factors Affecting Multifocal Electroretinogram: A mini review

“…Contact lenses are considered better than correction by spectacles (Hood et al, 2012;Hood et al, 2008;Marmor et al, 2003;Robson et al, 2018). In a recent investigation of the local differences in spherical and astigmatic defocus across the human retina using global-flash mfERG, it was found that responses from different retinal areas varied with local spherical defocus, but were not affected by astigmatic defocus (Turnbull et al, 2020). Further investigation is needed to fill the current gaps in information on the effects of hyperopia, presbyopia, and astigmatism on mfERG.…”