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Diana C Lozano, Michael D Twa; Quantification of Circumpapillary Retinal Thickness from Volumetric SD-OCT Images in Normal Rats and in a Rat Model of Glaucoma. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2102.
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Circumpapillary SD-OCT scans of the neural retina are routinely used to quantify structural changes in glaucoma. The purpose of this study was to evaluate structural changes in a rat model of glaucoma using computationally generated and scaled circumpapillary scans.
SD-OCT images were captured using the Spectralis system in 18 normal aged male Brown Norway rats (36 eyes; weight = 422 ± 32 g). Intraocular pressure was surgically elevated in six of these animals (6 eyes) by injecting hypertonic saline into an episcleral vein. Pre- and post-operative images were corrected for lateral magnification using individual ultrasonic axial biometric measurements. Circumpapillary scans (1 mm diameter) were generated from 30° x 25° horizontal volumetric image data sets centered on the optic nerve head. Global and regional (superior, inferior, nasal, and temporal) mean NFL/RGLC, NFL/RGCL+IPL, and total retinal thicknesses were calculated from the circumpapillary scans. Statistical comparisons of global mean thickness measurements between left and right eyes were assessed using a paired t-test, while regional analysis was evaluated using a one-way ANOVA with post-hoc pairwise comparisons.
Left and right eye NFL/RGCL thickness (95% CI: 33 - 38 µm vs. 34 - 39 µm; P = .6), NFL/RGCL+IPL thickness (95% CI: 78 - 85 µm vs. 79 - 86 µm; P = .5), and total retinal thickness (95% CI: 196 - 207 µm vs. 199 - 209 µm; P = .3) were not significantly different. In normal rats, mean temporal NFL/RGCL thickness (39 ± 6 µm) was significantly thicker than inferior (33 ± 5 µm) and superior (31 ± 5 µm) NFL/RGCL thickness. In the rat model of glaucoma, intraocular pressure was significantly higher (95% CI: 17 - 20 mm Hg vs. 21 - 43 mm Hg; P = .02) for 5 - 10 weeks after disease induction. Mean global NFL/RGCL+IPL thickness significantly decreased from 83 ± 11 µm to 73 ± 15 µm (P = .003) and mean global total retinal thickness decreased from 201 ± 13 µm to 170 ± 31 µm (P = .001).
The decrease in circumpapillary retinal thicknesses in the rat model of glaucoma correlated well with histological assessment of optic nerve damage (e.g. gliosis and collapse myelin sheaths). This result suggests that the in-vivo structural measurements are related to intraocular pressure elevation and not a magnification artifact.
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