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R. N. Nzokwe, H. Kecova, R. H. Kardon, S. A. Park, K. Hamouche, S. Jacobson, E. Alward, M. M. Harper, S. D. Grozdanic; Early Functional and Structural Optic Nerve Deficits in a Canine Model of Compressive Optic Neuropathy. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3842.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate functional and structural optic nerve deficits in a canine model of compressive optic neuropathy (CON).
CON was induced in healthy laboratory beagles (n=10) by implanting an expandable silicone implant into the orbital space. Controlled optic nerve compression was achieved by inflation of the implant with saline injection. Fluorescein angiography was performed to demonstrate perfusion of the optic nerve and retinal vasculature. Thickness of the retinal nerve fiber layer (RNFL) was evaluated using optical coherence tomography (Spectralis SD-OCT system), while pattern ERG (pERG) was recorded to evaluate retinal ganglion cell (RGC) function.
Despite relatively normal optic nerve perfusion observed by fluorescein angiography, orbital implant inflation resulted in significant pERG deficits immediately after induction of optic nerve compression (0.36+0.13 µV; mean+SEM; p<0.0001, Student’s t-test), when compared to control values (6.2+0.35 µV). OCT linear scans were obtained prior to pERG recordings and scan analysis showed significant increase in the RNFL thickness of area centralis (macula) region in CON dogs (39.54+1.849 µm) when compared to control dogs (26.35+1.53 µm, p<0.0001). Peripapillary circular scan analysis showed significantly decreased RNFL thickness in CON dogs (66.92+3.569 µm) when compared to controls (75.74+1.324 µm, p=0.0098). Linear correlation analysis showed statistically significant negative correlation between macular RNFL thickness and pERG amplitudes (r2= 0.43, p=0.03), while there was no statistically significant relationship between peripapillary RNFL thickness and pERG amplitudes.
Experimental optic nerve compression resulted in macular RNFL thickening and correlated with pERG deficits. Inclusion of blood vessel profile in the peripapillary RNFL analysis seems to decrease detection sensitivity and specificity for RNFL changes associated with compressive optic nerve injury in the dog model.
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