June 2017
Volume 58, Issue 8
Open Access
ARVO Annual Meeting Abstract  |   June 2017
The correspondence between OCT and histological measures in the optic nerve head region of a non-human primate model of glaucoma
Author Affiliations & Notes
  • Kwame Antwi-Boasiako
    College of Optometry, University of Houston, Houston, Texas, United States
  • Louvenia Carter-Dawson
    College of Optometry, University of Houston, Houston, Texas, United States
  • Margaret M Gondo
    College of Optometry, University of Houston, Houston, Texas, United States
  • Ronald S Harwerth
    College of Optometry, University of Houston, Houston, Texas, United States
  • Nimesh Bhikhu Patel
    College of Optometry, University of Houston, Houston, Texas, United States
  • Footnotes
    Commercial Relationships   Kwame Antwi-Boasiako, None; Louvenia Carter-Dawson, None; Margaret Gondo, None; Ronald Harwerth, None; Nimesh Patel, None
  • Footnotes
    Support  P30 EY007551, R01 EY001139, K23 EY021761
Investigative Ophthalmology & Visual Science June 2017, Vol.58, 4025. doi:
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      Kwame Antwi-Boasiako, Louvenia Carter-Dawson, Margaret M Gondo, Ronald S Harwerth, Nimesh Bhikhu Patel; The correspondence between OCT and histological measures in the optic nerve head region of a non-human primate model of glaucoma. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4025.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose : Glaucoma diagnosis is aided by assessing structural changes that occur at the posterior retina using technologies such as optical coherence tomography (OCT). Measures of the circumpapillary retinal nerve fiber layer (RNFL) thickness and the neural rim tissue in the optic nerve head (ONH) sample the majority of RGC axons in the eye. The purpose of this study was to investigate the correspondence between these in vivo measures and the histologically determined optic nerve axonal counts in a non-human primate model of glaucoma.

Methods : Unilateral experimental glaucoma was induced in 15 macaque monkeys (age 4-6 years) using argon laser energy to scar the trabecular meshwork. OCT scans (Spectralis HRA+OCT) were acquired and laterally scaled incorporating optical biometry data (Lenstar, LS900). Using radial scans centered on the ONH, the minimum rim width (MRW) was calculated as the shortest distance between the Bruch’s membrane opening (BMO) and inner limiting membrane (ILM). From 20x20 degree raster scans centered on the ONH, elliptical B-scans 550µm from the BMO were interpolated and used to quantify RNFL thickness, with major retinal vasculature removed. At varying stages of neuropathy, optic nerve sections (~0.5mm thick) were acquired 3-5mm posterior to the globe of each eye. Sections were fixed in 2.5% gluteraldehyde and 2% paraformaldehyde, post-fixed in 2% osmium tetroxide, dehydrated and embedded in epoxy resin. Thin sections were mounted on slides, stained for light microscopy. Images of 26 optic nerves were captured at high magnification (100X) and a semi-automated technique was used to count all of the axons (Bioquant Imaging System).

Results : The mean total axon count in the control eyes was 1,308,155 ± 108,382. Axon loss ratio (axons in experimental eye / control eye) ranged from 0.16 – 0.79. Axon count was linearly related to RNFL thickness (r2=0.96, p<0.01, slope=15,168) and an exponential rise to maximum fit best described the relationship with MRW (r2=0.86, p<0.01, AICc = 1.81).

Conclusions : In experimental glaucoma with mild to moderate RGC loss, the OCT derived RNFL and MRW measures are accurate estimates of RGC axonal content. The nature of the relationships suggests that tissue remodeling, rim tissue orientation and other non-neuronal changes could weaken the predictability of the MRW parameter during early stages of the optic neuropathy.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.

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