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A.S. Vilupuru, N.V. Rangaswamy, E.L. Smith, III, R.S. Harwerth; Optic Nerve Head and Nerve Fiber Layer in Normal and Glaucomatous Eyes of Monkeys . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3375.
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© ARVO (1962-2015); The Authors (2016-present)
To characterize the early structural changes from experimental glaucoma using optical coherence tomography (OCT) measurements of optic nerve head (ONH) and retinal nerve fiber layer (RNFL) parameters.
OCT images of the ONH and RNFL of both eyes of 14 rhesus monkeys (under anesthesia with dilated pupils) were obtained with the commercially available Stratus OCT system using standard, high density scans. Four of the monkeys had undergone monocular laser treatment of their right eyes to induce ocular hypertension and, of these, three showed glaucomatous visual field defects by behavioral assessment with standard clinical perimetry. Intra–subject (single subject on different dates) and inter–subject (across subjects) variabilities were calculated from the left eye measures. ONH and RNFL data from the right eyes of all the monkeys were analyzed to detect structural changes from glaucoma by calculating percent change with respect to the average left eye data.
ONH parameters showed larger intra– and inter–subject variability compared to RNFL parameters. RNFL intra–subject variabilities ranged between 3% (inferior thickness) and 7% (nasal thickness) and for ONH ranged between 6% (horizontal integrated rim width) and 66% (cup volume topography). Intra– and inter–subject variability in RNFL average thickness measures were 3% and 6%, respectively, compared to 10% and 23% for vertical cup–disc ratio (CDR). The comparison of the structural changes in eyes with experimental glaucoma indicated a primary change in vertical CDR of about 50% preceding the change in RNFL thickness.
The greater variability in ONH measures could be due to variation in the manual alignment of the instrument and from imaging artifacts created by large blood vessels. However, the results suggest that, even with the greater variability, the structural changes from experimental glaucoma can be detected earlier at the ONH than in RNFL. Longitudinal measures of ONH and RNFL pathological changes from experimental glaucoma using the OCT provide the potential for a better understanding of the timecourse of glaucomatous optic neuropathy.
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