Light adaptation of ex-vivo ERGs is limited after 6 weeks of diabetes

Abstract

Purpose : Light adaptation is essential for the eye to quickly adapt to increased background illumination and is mediated partly by dopamine. The effects of diabetes on light adaptation of light-evoked ex-vivo electroretinogram (eERG) recordings is not clear. Given the reduced retinal dopamine and dopamine receptor sensitivity in diabetes, we hypothesize that ERG light adaptation will be reduced in the diabetic retina.

Methods : Control (citrate buffer injected, n = 5) and diabetic (streptozotocin injected, n = 5) mice were dark adapted overnight 6 weeks after injections. Retinas were dissected, perfused with oxygenated Ringer’s solution, and placed in an eERG. Light-evoked eERG responses were recorded in the dark-adapted state at five increasing light intensities: 95, 9.5*10², 9.5*10³, 9.5*10⁴, 9.5*10⁵ photons/µm²s¹. Retinas were then exposed to a rod-saturating light intensity of 9.5*10² photons/µm²s¹ for 5 minutes and eERG recordings were repeated. Finally, retinas were exposed to a light intensity of 9.5*10³ photons/µm²s¹ for 5 minutes and eERG recordings were repeated. All light adapted amplitudes were normalized to the dark-adapted values for analysis. Two-way repeated measures ANOVAs were performed in GraphPad to compare A-wave and B-wave amplitudes between control and diabetic retinas.

Results : There is a significant decrease in the A-wave and B-wave amplitudes from the dark-adapted state after both light adaptation levels in control and diabetic retinas (p < 0.0001). However, there is a significantly smaller decrease in A-wave amplitude in the diabetic retinas after a 9.5*10² photons/µm²s¹ light adaptation in response to a 9.5*10⁵ photons/µm²s¹ light stimulation (p = 0.0248). There is also a significantly smaller decrease in B-wave amplitude in the diabetic retinas after 9.5*10³ photons/µm²s¹ light adaptation in response to a 9.5*10⁵ photons/µm²s¹ light stimulation (p = 0.0371).

Conclusions : Both control and diabetic retinas show robust reductions in response after light adaptation. However, both A and B waves amplitudes are partially preserved after light adaptation in the diabetic retinas. This indicates the diabetic retinas respond less to light adaptation than control retinas at the highest light stimulation intensity. Future experiments will explore how dopamine agonists and antagonists will affect eERG responses after light adaptation.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.