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A. S. Vilupuru, K.-M. Zhang, T. Lin, G. Ruiz, B. Feldmann, W. Orilla, Y. Li, C. Ghosn, J. Burke; Structural Changes Revealed by High Resolution OCT in a Monkey Model of Chronic Experimental Glaucoma. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4640. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To characterize the effects of chronic ocular hypertension (OHT) on retinal structure using high resolution Fourier Domain OCT (FD OCT) and Time Domain OCT (TD OCT) in a primate model of experimental glaucoma and compare it with retinal function measured by photopic negative response (PhNR) of the ERG.
Sixteen anesthetized cynomolgus monkeys weighing 2.8-6.9 kg with unilateral chronic OHT induced by circumferential laser photocoagulation of the trabecular meshwork were used in this study. A FD OCT (Topcon 3D OCT-1000) was used to obtain raster scans (6 mm x 6 mm, 64 b-scans, 512 a-scans/b-scan) centered on the optic nerve head (ONH) and on the fovea to measure peripapillary nerve fiber layer (NFL) and macular thickness. A Stratus OCT (TD OCT) system was used to measure the NFL and macular thickness using standard scanning protocols (512 a scans). Intraocular pressure (IOP) was measured using a pneumatonometer (Mentor O&O) and PhNR was measured with brief red flashes on a rod-saturating blue background using the Espion system (Diagnosys LLC). All measurements were made in both eyes and the data are expressed as mean ± SD.
Median time of chronic experimental OHT was 4 years (range: 3 to 15). The most recent IOP’s in glaucomatous and fellow, normal eyes were 38 ± 10 and 20 ± 3 mm Hg respectively. Average NFL thickness in the normal eye was 93 ± 12 with TD and 83 ± 11 microns with FD OCT. In glaucomatous eyes with severe NFL loss (>75%) the TD OCT NFL segmentation included part of inner retina resulting in over-estimation of NFL. Average loss in NFL thickness in OHT eye relative to the normal eye was therefore smaller in TD OCT (35 ± 22%) compared to FD OCT (61 ± 34%; p = 0.014). There was no significant difference (p = 0.44-0.90) between FD and TD OCT on macular thickness changes between OHT and normal eyes. Central, inferior, superior, nasal and temporal macular thickness changes were 4 ± 4, 11 ± 6, 9 ± 5, 7 ± 5 and 11 ± 5 % respectively in FD OCT and the corresponding values in TD OCT were -4 ± 10, 8 ± 13, 8 ± 10, 6 ± 9 and 9 ± 12 %. The PhNR was reduced by 79 ± 21% in the OHT eye and was significantly correlated with FD OCT NFL loss (r = 0.69, p < 0.05). In 5/16 glaucomatous eyes FD OCT showed "cyst like" changes in the macular inner nuclear layer.
High resolution FD OCT can measure greater NFL loss compared to TD OCT in a primate model of experimental glaucoma. Structure and function showed good correlation in this cross-sectional analysis of chronic experimental glaucoma. High resolution imaging improves the ability to track NFL changes over a larger dynamic range especially in end-stage glaucoma.
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