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Annie Oh, Christine Harman, Kristin Koehl, Jiayan Huang, Leandro Teixeira, Laurence Occelli, Eric Storey, Gui-Shuang Ying, Andras Komaromy; Spectral-Domain Optical Coherence Tomography of the Optic Nerve Head in a Canine Model of Primary Open-Angle Glaucoma. Invest. Ophthalmol. Vis. Sci. 2013;54(15):4893.
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Inherited primary open-angle glaucoma (POAG) in Beagle dogs is a well established large animal model of glaucoma, and it is caused by a G661R missense mutation in the ADAMTS10 gene. This study represents the first attempt to describe early glaucomatous optic neuropathy by spectral-domain optical coherence tomography (SD-OCT).
The optic nerve heads (ONHs) of 9 adult, glaucomatous dogs (mean age +/- SD: 43 +/- 2.5 months; mean diurnal intraocular pressure (IOP): 29.9 +/- 1.1 mmHg) and 3 related, age-matched control dogs (IOP: 18.0 +/- 1.3 mmHg) were imaged under general anesthesia by SD-OCT (Spectralis®, Heidelberg Engineering). All of the dogs were sighted with normal retinal function as recorded by flash electroretinography. The thickness of the peripapillary retina was measured at 8 locations, and ONH dimensions were evaluated in the horizontal and vertical planes. OCT measurements were compared between affected and control dogs by ANOVA. The correlations of OCT measurements with IOP and axial globe length were assessed by Spearman correlation coefficient. OCT images from affected and control dogs were compared qualitatively with selected histologic ONH sections.
There were no significant differences in the thickness of any retinal layers evaluated between glaucomatous (mean full retinal thickness: 239 +/- 6.0 μm) and normal control dogs (243 +/- 3.2 μm). Compared to histologic cross-sections, OCT images showed that the normal canine ONH protruded more noticeable into the vitreous. Of all the ONH parameters evaluated, the loss of neuroretinal rim height in the horizontal plane was most significant (from 154 +/-38.4 μm to 9.3 +/- 22.1 μm; p < 0.01). Furthermore, there was a highly significant negative correlation between neuroretinal rim height and IOP (Spearman correlation: -0.86; p<0.0001). Even though the cupping of the ONH dramatically worsened in a few affected dogs, the average cup dimensions were not significantly different between glaucomatous and normal control dogs.
SD-OCT is a useful tool to detect early glaucomatous optic neuropathy in dogs. The decrease in neuroretinal rim height without inner retinal thinning and without obvious functional loss suggests that initial degenerative changes are mostly due to loss of myelin.
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