Expansion of the subretinal space and the hyporeflective band reflect two linked aspects of light-induced OCT responses in the outer retina: pH and metabolic activity

Abstract

Purpose : To test the hypothesis that two light-evoked OCT indices in the outer retina, subretinal space elongation and appearance of a hyporeflective band, are correlated, and reflect two stages in an outer retinal signaling pathway.

Methods : OCT images were captured with a dark-light paired design for each of following mice: i) with different backgrounds, ii) with modified inner retinal function (nob7 and nob2), iii) during metabolic stimulation [protonophore 2,4-Dinitrophenol (DNP)], and iv) during acidosis [acetazolamide (ACZ)]. Outer retina thicknesses were measured from ELM to RPE basal, and hyporeflective band intensities were calculated from the averaged OCT intensity profile.

Results : Light-adaptation induced outer retina (ELM-RPE) elongation in all strains. Mutations in either the ON retinal pathway (nob7) or with impaired photoreceptor synaptic transmission (nob2) did not affect this photoresponse when compared with their respective littermates. However, C57 mice showed larger response amplitudes than mice in other genetic backgrounds. The hyporeflective band intensities had a high correlation (R² = 0.915) with ELM-RPE thickness changes for all mice groups with different genetic backgrounds. Although metabolic stimulation by DNP produced a parallel reduction in the light-evoked ELM-RPE thickness and the hyporeflective band, only ACZ-induced retinal acidosis inhibited the light-evoked ELM-RPE expansion but without light-evoked changes in the hyporeflective band intensity.

Conclusions : For the first-time, a correlation is found between two OCT outer retina photoresponses. These studies support the hyporeflective band intensity as sensitive to an upstream signal of light-based metabolic activity and the ELM-RPE thickness as sensitive to a downstream pH-specific signal.

This is a 2020 ARVO Annual Meeting abstract.