Optical coherence tomography and histologic measurements of nerve fiber layer thickness in normal and glaucomatous monkey eyes

PURPOSE. To investigate optical coherence tomography (OCT) measurements of retinal nerve fiber layer (RNFL) thickness change associated with elevated intraocular pressure (IOP) over a period of time, and to compare in vivo OCT RNFL thickness measurements with morphologic measurements of the same tissues. METHODS. One eye of each of 12 cynomolgus monkeys was treated with argon laser to the anterior chamber angle to induce elevated IOP. OCT measurements were made weekly in the treated and the contralateral eyes of each monkey for 14 weeks after the laser insult. The monkeys were killed at the conclusion of the experiment, and comparisons were made between the terminal OCT RNFL measurements and quantitative histomorphometric assessments in the same eyes. Effects of exposure to elevated IOP on RNFL were characterized by a mixed-effects model. Linear mixed-effects models provided unbiased analysis of balanced and unbalanced repeated-measures data, detection of group effects (fixed effects), and individual subject effects (random effects), thereby making the best use of all available data. RESULTS. Increased IOP was achieved in 10 eyes. Exposure to high IOP was associated with the loss of mean RNFL thickness at a median rate of 3.77 ± 0.08 μm/wk. On average, OCT RNFL thickness measurements were higher than histomorphologic measurements by 5.7 μm (95% confidence interval, 3.6-7.8; P = 0.003). CONCLUSIONS. Thinning of the RNFL associated with elevated IOP was demonstrated with OCT in a group of experimentally glaucomatous monkey eyes over a period. OCT measurements corresponded with histomorphometric measurements of the same tissues.