Effects of short-term moderate versus high intraocular pressure elevation on flicker-induced changes in full- field electroretinogram

Purpose Transient flickering light stimulation (FLS) enhances the electrical activity in the middle retinal layer (MRL) of wild-type mice. This study investigates how short-term moderate and high intraocular pressure (IOP) elevation influences flicker-induced enhancement in the retinal activity using full-field electroretinogram (ffERG). Methods Baseline blood pressure (BP), IOP, mean ocular perfusion pressure (OPP), and ffERG were measured before and after FLS in eighteen C57BL6J mice. The mice were subsequently divided into two groups: ocular hypertension (OHT, n = 9) and control (n = 9). In the OHT group, IOP was firstly transiently elevated to ~  35 mm Hg for 5 minutes (termed as Loop on Phase-1 (LOP-1)) using an adjustable vascular loop in one randomly chosen eye, while the control group had the loop placed without IOP elevation. IOP was further elevated to ~  65 mm Hg in the same eye for another 5 minutes (termed as Loop on Phase-2 (LOP-2)) in the OHT group, while the control group had the loop placed in the same eye without IOP increase. The BP, IOP, mean OPP and ffERG measurements were repeated before and after FLS in each condition. Results While BP showed no significant differences, mean OPP was significantly reduced at LOP-1 and LOP-2 in the OHT group compared to both baseline (p < 0.001) and the control group (p < 0.001). The b-wave amplitudes recorded after FLS were significantly higher than those before FLS at baseline and LOP-1 conditions in both control (p < 0.01) and OHT groups (p < 0.001). In the LOP-2 condition, the OHT group showed no significant difference (p > 0.05) between pre- and post-FLS b-wave amplitudes, while the control group exhibited a significant increase (p < 0.001). The percentage change in b-wave amplitude was significantly reduced in the OHT group at LOP-2 condition (Pre-Loop vs LOP-2: p < 0.01; LOP-1 vs LOP-2: p < 0.001), while the control group maintained a consistent percentage increase in b-wave amplitudes. No such significant changes were found in other parameters of ffERG response after FLS. Conclusions Short-term high IOP elevation (~ 65 mm Hg), but not moderate (~ 35 mm Hg), disrupted flicker-induced enhancement of MRL electrical activity. This implies that the retina can adapt to a short period of moderate IOP, sustaining a normal increase in the retinal electrical activity in response to FLS. However, even a short period of high IOP would cause certain physiological damage to the retina.