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Y.H. Kwon, S.D. Grozdanic, D.M. Betts, D.S. Sakaguchi, R.H. Kardon, I.M. Sonea; Functional Assessment of the Retina and Optic Nerve in the Rat Model of Chronic Ocular Hypertension . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3327.
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Purpose: To functionally characterize the rat retina and optic nerve after chronic elevation of the intraocular pressure (IOP) using electroretinography (ERG) and automated pupillometry. Methods: We induced obstruction of aqueous humor outflow in 11 adult Brown Norway rats by injection of indocyanine green dye (ICG) into the anterior chamber, followed by diode laser treatment (60 spots) of the episcleral veins enriched with the dye. Direct and indirect pupil light reflexes (PLR) were recorded from the unoperated eye, and ERGs were recorded from the operated and control eyes preoperatively and postoperatively. Results: Laser treatment induced significant elevation of the IOP in operated eyes (mean preop=15.5mmHg, 3d postop=28.1, 7d=33.4, 14d=35, 21d=29.3, 28d=31.2, 35d=26.7, 42d=24.2 and 60d=19.4 mmHg). Preoperative pupillary light reflex (PLR ratio(indirect/direct)) was 68.5+4%. Despite significant elevation of the IOP, PLR values were not significantly decreased (60.3+10.3%; p>0.1) 3 days postoperatively compared to preoperative values. Starting day 7 postoperatively the PLR function started to decrease (7d postop=14.6+8%, 14d=11.5+6.7% and 21d=12.6+4%, p<0.01). ERG analysis of operated eyes revealed significantly decreased amplitudes of a- (p<0.001) and b-waves (p<0.001) 10d postoperatively, while oscillatory potentials (OPs) and flicker ERG (flERG) amplitudes were not detectable (Ratio of operated/control=0). However, 28 days postoperatively PLR and OPs partially recovered (PLRratio=38.5+8.6%, p<0.01; OPratio= 7.5+2.3%, p<0.001), while a- wave, b-wave and flERG amplitudes did not significantly changed compared to values observed 10d postoperatively. Starting day 35 postoperatively the PLR function started to decrease again (PLR ratio=17.2+7.4%, 35d postop; 9.5+7.3%, 42d postop) and was 4.2+4% at the last observed time point (60d postop). The ERG analysis of the operated eyes revealed dramatically reduced a-wave (Ratio of operated/control=8.9+2.7%), and b-wave amplitudes (Ratio of operated/control=7.8+2.5%), while OPs and flERG did not have recordable amplitudes 60 days postoperatively. Histological analysis revealed degeneration of all retinal layers (predominantly inner retina layers) and massive degeneration of the optic nerve axons. Conclusions: The function of the retina and optic nerve decreases significantly in a rat model of chronic ocular hypertenstion.
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