EC Ophthalmology

Purpose: To examine the effect of optical chromatic defocus conditions on retinal activity using multifocal-electroretinogram (mf-ERG).

Method: Twelve emmetropic adults (aged 22 to 29 years) with normal ocular health participated in the study. Mf-ERG was performed six times on both eyes. The experimental conditions were: no defocus, positive defocus (+2D), and negative defocus (-2D) conditions with short-pass (blue), long-pass (red), and neutral density (ND) filters. A multifocal-ERG with hexagonal stimulus pattern subtended 60^o horizontally and vertically at a working distance of 33 cm. The amplitudes and implicit times of wave components of mf-ERG responses were pooled into five concentric rings for analysis.

Result: Among the experimental conditions, the retinal P1 amplitude demonstrated a significant change between long-pass and short-pass (20.03 ± 12 nV/deg² and 15.14 ± 9 nV/deg², respectively) (P < 0.05). There was a significant interaction between color filters and type of defocus (p < 0.05). With the long-pass filter, myopic defocus showed a higher P1 amplitude (20.5 ± 10 nV/deg²) compared to hyperopic defocus (18 ± 10 nV/deg²), whereas the blue filter demonstrated a higher amplitude with hyperopic defocus (17 ± 8 nV/deg²) than with myopic defocus (14 ± 10 nV/deg²). Only central and paracentral retinal regions showed a significant amplitude change to chromatic blur. The implicit time was significantly lower (relatively faster) in peripheral retinal regions with no significant difference across all tested conditions.

Conclusion: Showed that chromatic blur caused small but significant changes in mf-ERG amplitudes that are limited to central and paracentral retina, where long-pass filters induced more mf-ERG amplitude under myopic defocus. To better understand whether the shift in the ocular chromatic aberration is one of the cues that the retina uses to differentiate myopic and hyperopic defocus, further studies that account for the posterior ocular shape, peripheral refraction, and off-axis ocular aberrations with a larger sample are required.

Keywords: Chromatic; Defocus; Retinal Response; Electroretinogram; Myopia

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