Electrophysiological and psychophysical studies of meridional anisotropies in children with and without astigmatism

Tiong Peng Yap, Chi D. Luu, Catherine M. Suttle, Audrey Chia, Mei Ying Boon

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Abstract

PURPOSE. We investigated the pattern of meridional anisotropies, if any, for pattern onset- offset visual evoked potential (POVEPs) responses and psychophysical grating acuity (GA) in children with normal letter visual acuity (20/20 or better). METHODS. A total of 29 children (aged 3-9 years), nine of whom were astigmatic (AS), were recruited. Orientation-specific monocular POVEPs were recorded in response to sinewave grating stimuli oriented along the subjects’ principal AS meridians. Horizontal and vertical gratings were designated Meridians 1 and 2, respectively, for nonastigmatic patients (Non-AS). Binocular POVEPs in response to the same stimuli, but oriented at 45°, 90°, 135°, and 180°, were recorded. Psychophysical GAs were assessed monocularly and binocularly along the same meridians using the same stimuli by a 2-alternative-forced-choice staircase technique. The C3 amplitudes and peak latencies of the POVEP and GAs were compared across meridians using linear mixed models (monocular) and ANOVA (binocular). RESULTS. There were significant meridional anisotropies in monocular C3 amplitudes regardless of astigmatism status (P = 0.001): Meridian 2 (mean ± SE Non-AS, 30.13 ± 2.07 µV; AS, 26.53 ± 2.98 µV) was significantly higher than Meridian 1 (Non-AS, 26.14 ± 1.87 µV; AS, 21.68 ± 2.73 µV; P = 0.019), but no meridional anisotropies were found for GA or C3 latency. Binocular C3 amplitude in response to horizontally oriented stimuli (180°, 29.71 ± 3.06 µV;) was significantly lower than the oblique (45°, 36.62 ± 3.05 µV; P = 0.03 and 135°, 35.95 ± 2.92 µV; P = 0.04) and vertical (90°, 37.82 ± 3.65 µV; P = 0.02) meridians, and binocular C3 latency was significantly shorter in response to vertical than oblique gratings (P ≤ 0.001). CONCLUSIONS. Meridional anisotropy was observed in children with normal vision. The findings suggest that horizontal gratings result in a small, but significantly lower POVEP amplitude than for vertical and oblique gratings.

Original languageEnglish
Pages (from-to)1906-1913
Number of pages8
JournalInvestigative Ophthalmology and Visual Science
Volume60
Issue number6
DOIs
Publication statusPublished - May 2019
Externally publishedYes

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