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P. P. Ko, G. Gum, R. A. P. de Carvalho; Evaluation of the Photopic Negative Repsonse and Oscillatory Potentials in New Zealand White Rabbits With Retrobulbar Optic Neuropathy and Elevated Intraocular Pressure Following Intracameral Injection of 1% Methylcellulose and Vortex Vein Ligation. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5486.
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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.
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.
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.
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.
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