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Gillian J. McLellan, Elyse Kleifgen, Paul L. Kaufman, Carol A. Rasmussen; Detection Of Early Structural Changes By SD-OCT In A Feline Model Of Congenital Glaucoma. Invest. Ophthalmol. Vis. Sci. 2012;53(14):2493.
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To characterize early structural changes in the optic nerve head (ONH) and retinal nerve fiber layer (RNFL) in a feline model of primary congenital glaucoma (PCG).
Cirrus SD-OCT (Carl Zeiss Meditec Inc., Dublin, CA) was used to acquire optic nerve cube scans in cats ranging in age from 0.5-6.5 yrs. These included 15 young PCG cats (0.68 ± 0.28 years); 23 young normal cats (0.84 ± 0.23 years); 8 adult PCG cats (4.35 ± 1.14 years), and 3 adult normal cats (4.79 ± 0.98 years). At least 3- 5 separate scans were acquired per eye and scans excluded from analysis if the animal’s IOP was >45 mmHg. Scans with signal strength <8/10; areas of signal drop-out, or errors in automated segmentation of retinal layers were excluded from analysis. Differences between groups were evaluated by Student's t-test or ANOVA, with p<0.05 considered significant.
Compared to normal age-matched cats, young PCG cats showed significant differences in ONH parameters by 6 months of age, including increase in Cup Volume ; Vertical cup/disc ratio (CDR), and average CDR but these parameters did not subsequently change significantly with age in PCG. Average RNFL thickness was not significantly different in young PCG cats (63.95± 7.85 μm) compared to normal cats (64.4± 6.72 μm). Inferior quadrant RNFL thickness was however significantly decreased by 6 months of age in PCG cats compared to age-matched controls (p=0.013). Thinning in all other RNFL quadrants was noted in adult PCG cats and average RNFL thickness values were significantly less in the adult PCG cats (51.146 ± 4.44 μm) compared to the younger PCG cats as well as adult controls (60.61 ± 3.24 μm).
As early as 6 months of age, PCG cats show pronounced posterior displacement of the lamina cribrosa that persists on normalization of IOP; with changes in ONH parameters and thinning of the RNFL in the inferior quadrant consistent with glaucomatous damage. As the disease progresses more generalized RNFL thinning occurs. Studies are ongoing to correlate these structural changes with electrophysiological functional measures and histological evidence of optic nerve axon loss
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