Abstract
Purpose :
Studies show that glaucoma patients exhibit a reduction in the photopic negative response (PhNR), which is a measure of retinal ganglion cell function. Across animal models, acute elevations of intraocular pressure (IOP) also diminish the PhNR. We have previously demonstrated that transient elevation of IOP also results in a selective reduction in PhNR amplitude and that this loss is dependent on ocular perfusion pressure. To investigate the initial cellular responses to elevated IOP in the living human eye, we sustain elevation in IOP along with a selectively diminished PhNR for a prolonged amount of time. We hypothesize that a non-ischemic level of IOP elevation will selectively diminish the PhNR amplitude over the course of many hours.
Methods :
Three research-consented brain-dead organ donors underwent screening for inclusion criteria. Blood pressure was measured systemically via an arterial line, and tonometry was performed using either an applanation (Tono-Pen AVIA, Reichert, Depew, NY) or a rebound tonometer (IC200, iCare, Vantaa, Finland). PhNR was measured using modified full field electroretinography (RETeval, LKC Technologies, Gaithersburg, MD) with DTL Plus silver nylon thread electrodes (Diagnosys, Lowell, MA). The experimental eye received an injection of viscoelastic (DuoVisc, Alcon, Fort Worth, Texas; Healon, Johnson & Johnson, North Jacksonville, FL) to achieve an IOP of 30 – 40 mmHg while the fellow eye served as a control. Blood pressure, IOP, and PhNR were recorded every 2 hours until organ procurement.
Results :
In all three research-consented brain-dead organ donors, elevated IOP selectively diminished the PhNR amplitude from the time of IOP elevation until organ procurement (difference: -8.67 ± 3.59 µV, paired t-test, t(2) = 4.18, p = 0.0264, one-tailed). The a-wave (paired t-test, t(2) = 1.40, p = 0.1482, one-tailed) and b-wave (paired t-test, t(2) = 2.31, p = 0.073, one-tailed) amplitudes were largely unaffected by the increases in IOP.
Conclusions :
Sub-ischemic, prolonged IOP elevation persistently diminishes the PhNR response of the inner retina without substantially altering responses of the outer retina. Fluctuations in amplitudes are affected by variation in IOP, blood pressure, and, consequently, ocular perfusion pressure. Sustaining this response for a prolonged period of time will be of use in future investigations into early cellular responses to ocular hypertension.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.