Chromatic Electroretinography in Non-human Primates with and without PDE6C-associated Achromatopsia

Abstract

Purpose : Rhesus macaques have trichromatic vision like humans. Chromatic electroretinography (ERG) can be used to isolate the three different cone subtypes to interrogate their function. Herein, we describe a custom chromatic ERG technique using the RetEvet device (LKC Technologies) in rhesus macaques (Macaca mulatta) wildtype (WT) or homozygous for a PDE6C R566Q mutation that causes achromatopsia.

Methods : Fourteen WT controls and six rhesus macaques homozygous for the p.R656Q mutation were evaluated under anesthesia using photopic chromatic ERG following pupillary dilation. For short wavelength, animals were stimulated with a blue flash (1.0 cd/m2 at 4.2 Hz) on red background (560 cd/m2). For medium wavelength, a green flash (1.0 cd/m2 at 4.2 Hz) on red background (160 cd/m2). For long wavelength, a red flash (1.0 cd/m2 at 4.2 Hz) on blue background (10 cd/m2) was used. Data are presented as mean ± SD and compared using one way ANOVA.

Results : Short, medium and long wavelength responses were isolated and demonstrated in WTs. The short wavelength (blue flash on red background) had an a-wave amplitude of -13.9 ± 3.4 µV (13.8±1.2 ms) and b-wave amplitude of 53.1 ± 16.7 µV (27.9±2.6 ms). The medium wavelength (green flash on a red background) had an a-wave amplitude of -10.0 ± 7.6 µV (14.3±1.2 ms) and b-wave amplitude of 42.0 ± 14.3 µV (27.6±3.8 ms). The long wavelength (red flash on a blue background) had an a-wave amplitude of -10.9 ± 3.5 µV (14.9±1.25 ms) and b-wave amplitude of 41.5 ± 11.8 µV (28.4±3.1 ms). The a- and b-wave amplitudes and times did not significantly differ between the three cone subtypes in WTs (P > 0.05). As expected, typical chromatic ERG activity attributed to cones was absent in PDE6C R566Q homozygotes, though a waveform consistent with incomplete suppression of rod activity was observed in the medium and short wavelength tests. These positive waveforms were measured at 6.25 ± 9.72 µV (12.2 ± 20.3 ms) in the medium wavelength and 4.35 ± 3.3 µV (31.3 ± 11.7 ms) in the short wavelength. Both the medium and short wavelength tests use a red background to suppress the other cone subtypes, which may incompletely suppress rod function.

Conclusions : Chromatic electroretinography can be performed successfully utilizing the RETevet device. Applications of this technique include investigation of color vision in NHPs as well as response to gene therapy targeting cone photoreceptors.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.