# Effects of angle of incidence of stimulus light on photopic electroretinograms of zebrafish larvae

## TL;DR

This study shows that the angle of light used in electroretinogram recordings affects the response in zebrafish larvae, suggesting that using a full-field light stimulus is better for maximum results.

## Contribution

The study demonstrates that the angle of stimulus light affects photopic electroretinogram amplitudes in zebrafish larvae.

## Key findings

- Stimulus light at 0° produces significantly larger b-wave and d-wave amplitudes compared to 30° dorsal and ventral angles.
- Implicit times of the b- and d-waves are not significantly affected by the angle of stimulus light.
- Using a ganzfeld stimulus is recommended to maximize photopic ERG amplitudes in zebrafish larvae.

## Abstract

In electroretinographic (ERG) recordings of zebrafish, the light stimulus is usually delivered by a fiber optic cable. The purpose of this study was to determine whether the angle of incidence of the stimulus light from the fiber optic cable will affect the amplitudes and implicit times of the ERGs of zebrafish larvae. The larvae were positioned on their side with the right eye pointed upward. The light stimuli were delivered by a fiber optic cable from three directions of the larvae: frontal 0° (F0°), dorsal 30°(D30°), and ventral 30°(V30°). Photopic ERGs were recorded from 16 larvae at age 5–6 days post-fertilization. Our results showed that the mean amplitude of the b-wave elicited at D30° and V30° stimulation was significantly smaller than that elicited at F0° stimulation (P = 0.014 and P = 0.019, respectively). In addition, the mean amplitude of the d-wave elicited at D30° and V30° stimulation was significantly smaller than that elicited at F0° stimulation (P < 0.0001 and P = 0.015, respectively). However, the difference between the b-wave amplitudes elicited at D30° and V30° stimuli were not significant (P = 0.98), and the d-wave amplitudes were also not significantly different (P = 0.20). The average b-wave amplitudes elicited at D30° stimulation was 84.6 ± 15.7% and V30° stimulation was 84.8 ± 17.4% relative to that of F0° stimulation. The average d-wave amplitudes elicited by D30° stimulation was 85.5 ± 15.2% and by V30° stimulation was 79.0 ± 11.0% relative to that of F0° stimulation. The differences in the implicit times of the b- and d-wave elicited by the different directions of stimulation were not significant (P = 0.52 and P = 0.14, respectively). We conclude that the amplitude of the photopic ERGs is affected by the angle of the incident light. Thus, it would be better to use ganzfeld stimuli to elicit maximum b- and d-wave amplitudes of the photopic ERGs of zebrafish larvae.