Abstract
Purpose: :
The objective of this study was to evaluate the electroretinogram (ERG) photopic negative response(PhNR) & oscillatory potentials(OPs) in three models of retinal ganglion cell(RGC) loss due to traumatic-induced retrobulbar optic neuropathy(TIRON) or increased intraocular pressure (IOP) in New Zealand White rabbits following intracameral injection of 1% Methyl Cellulose or vortex vein ligation.
Methods: :
Ten New Zealand White rabbits received in the right eye an intracameral injection of 0.125 mL of 1% methyl cellulose after an equal volume of aqueous humor was collected from a separate intracameral port. In the second group, the right eye had three out of four vortex veins ligated. In the third group, a vascular clamp with pressure of 50g and 125g was applied to six rabbits' right retrobulbar optic nerves for one minute & released. Clinical progression was evaluated by ERG, fundus color photography, fluorescein angiography(FA) & Ocular Coherence Tomography(OCT). ERG, IOP, OCT, fundus color photography, FA & ophthalmic observations were performed at multiple time points throughout the study. All rabbits were scotopically adapted for 60 minutes prior to the ERG procedures. ERGs were recorded with a 20 msec stimulus of scotopic & photopic luminance. ANOVA statistical analysis was performed.
Results: :
In eyes with vortex vein ligation, the amplitudes of ERG PhNR and OP had declined progressively over time compared with the baseline. By Day 9, the mean PhNR amplitudes at +5dB decreased by an average of 50% (p=0.0210) and by 30% at +12.5dB (p=0.1625) after vortex veins ligation. In the eyes after intracameral injection, the mean PhNR amplitudes at +5dB decreased by an average of 38% (p=0.1434). After retrobulbar optic nerve clamping, the mean PhNR amplitudes at +5dB decreased by an average of 28% (p<0.05) by day 16. The ERG data showed that the decreased amplitudes of PhNR correlated with the increased IOP & TIRON progression.
Conclusions: :
The decreased amplitudes of PhNR & OP indicate the damage at the RGC & inner retinal plexiform layers. These ERG parameters have the potential to monitor in vivo the effect of pharmacological interventions to prevent or slow down cell loss at RGC & inner retinal plexiform layers.
Keywords: ganglion cells • intraocular pressure • optic nerve