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Allison Umfress, Brian J Carlson, Wendi S Lambert, David J Calkins; Early Changes in Retinal Layers Detected In Vivo Following Microbead-Induced Ocular Hypertension. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2412.
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© ARVO (1962-2015); The Authors (2016-present)
Neurodegeneration in glaucoma is characterized by early deficits in retinal ganglion cell axon function in the optic projection. Here, we tested whether optical coherence tomography (OCT) could detect changes in retinal layer thickness in vivo following short-term elevations in ocular pressure in mice induced by microbead injection.
We induced ocular hypertension (OHT) in 3 month C57 mice (n=10) through microbead occlusion (1 ul) of the anterior chamber and monitored ocular pressure using TonoLab rebound tonometry. The contralateral eye received an equivalent volume saline injection. OCT imaging was performed weekly over 2-3 weeks using the Bioptigen Envisu R2200 VHR Rodent OCT with InVivoVue Clinic Acquisition software. Images were taken in each eye at nine locations using the optic nerve head as register. Data including retinal layer thickness were analyzed with the Bioptigen InVivoVue Diver 2.0 Software using the Retina Template panel.
Consistent with published results, microbead-injected eyes exhibited an elevation in IOP of about 30% compared to their saline-injected counterparts. Compared to baseline, 2-3 weeks of OHT induced an 8% increase in retinal nerve fiber layer thickness (p=0.002); thickness in the saline eye remained the same (p=0.10). Over the same period, thickness of the inner plexiform layer varied greatly in both eyes over a range of 38-60 um, with thickness in the OHT retina on average 4% less (p=0.04)
Our results indicate that even short-term elevations in IOP induced by microbead occlusion are associated with detectable changes in retinal layer thickness as measured by OCT. In particular, prior to axon loss in this model, which occurs after 5-6 weeks of OHT, the retinal nerve fiber layer actually increases in thickness. This change likely reflects early stages of ganglion cell axonopathy and could be utilized as a surrogate biomarker for onset of pathogenesis.
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