Abstract
Purpose :
We previously have described an electroretinogram (ERG) protocol, based on rod-cone interaction, that reflects retinal horizontal cell (HC) function. We have validated the protocol in a horizontal-deficient knock-out mouse and have shown horizontal cell function and structure loss in a rat model of traumatic brain injury (TBI) from blast overpressure. Here, we report the results of HC testing in TBI patients as well as in patients having a variety of different diagnoses.
Methods :
The ERG protocol consists of taking the ratio of b-wave amplitudes obtained by flashing a bright light (0.50 log cd.s/m2) onto a dim background (1 cd/m2), to flashing a light of the same luminance (0.50 log cd.s/m2) onto a bright background (30 cd/m2). The flash on a bright background is an isolated cone response and is defined as such in the International Society for the Clinical Electrophysiology of Vision (ISCEV) protocol. Rods contribute to 30-40% of the amplitude of the ERG recorded on the dim background; the rest arise from dark-adapted cones. All patients who were referred for clinical testing underwent standard ERG testing in addition to the 1 extra flash required by this protocol and any additional testing that might better elucidate function changes specific to their condition.
Results :
On average, b-wave amplitudes on the dim background were 1.24 times larger than responses on the bright background in normal observers and in most patients, even though the background light was 30 times dimmer (n = 49, sd = 0.24). Nine patients had ratios that were significantly elevated (X = 2.13, sd = 0.30, p < 0.0001, unpaired t-test), and the distributions of ratios from the 2 populations did not overlap. Patients with TBI, with rod dystrophies, or who were taking the anti-epileptic drug vigabatrin showed elevated ratios (reduced HC function), unlike patients with a variety of other conditions including cone dystrophy, Stargardt’s disease, MEWDS, concomitant rod-cone dystrophy, and chronic open angle glaucoma along with other optic neuropathies. Interestingly, the elevated ratios were cause solely by a reduction in the isolated cone-response (r = 0.40, p < 0.001), which indicates that this measure of cone function can be affected by HC function in the presence of normal cones.
Conclusions :
Rod-cone interaction, as modulated by horizontal cells, can be abnormal in patients with TBI, in patients who are taking vigabatrin, and in patients who have rod dystrophies.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.