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G. A. Cull, B. Fortune, L. Wang, G. A. Cioffi; Longitudinal Structural Evaluation of Experimental Retinal Nerve Fiber Layer Defects in Rhesus Monkeys. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3343.
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© ARVO (1962-2015); The Authors (2016-present)
To compare longitudinal results from confocal scanning laser ophthalmoscopy (CSLO), scanning laser polarimetry (SLP), and optical coherence tomography (OCT) after initiation of an experimental retinal nerve fiber layer defect (ERNFLD).
Four Rhesus Monkeys had retinal laser burns placed in an arc around the optic disc (~1.5mm from the margin with arc length ~45o) to create an ERNFLD in one eye each. Measurements of retinal nerve fiber layer thickness (RNFLT) were obtained weekly for one month prior to, and 5 weeks after laser in both experimental and fellow control eyes by CSLO (HRT1), SLP (GDx VCC), and OCT (Stratus). Additional evaluation of retinal and optic disc structure included stereophotography and OCT measurements of the macular and burn site. RNFLT estimates were exported for a 3.4 mm diameter circle centered on the optic nerve head for all 3 instruments, and compared over time before and after laser.
During pre-laser baseline, RNFLT estimates were more consistent between sessions, and between right and left eyes for SLP and OCT as compared to CSLO. The average RNFL thickness was 45.9 ± 8.3, 95.4 ± 12.1, and 147.2 ± 30.7 for SLP, OCT, and CSLO, respectively. After laser, one animal was immediately omitted from the study because of complications (intra- and sub-retinal hemorrhage). One week after laser, a statistically significant ERNFLD was present in 2/3 eyes by SLP but not by OCT or CSLO. Between weeks 1 and 3, RNFLT estimates by the OCT, increased then declined in 3/3 eyes. At week 4 a statistically significant ERNFLD was present in 3/3 eyes for both SLP and OCT. CSLO never indicated any RNFL defect.
In this small group of monkeys, OCT provided the most reproducible estimate of normal RNFLT, closely followed by SLP. CSLO estimates of RNFLT were less repeatable and also insensitive to detect ERNFLD. SLP detected the ERNFLD prior to OCT and CSLO. The pattern of results suggests that OCT detected axonal swelling during early stage damage, but that birefringent elements were already disrupted. The discrepancies between SLP and OCT RNFLT estimates may be informative about the pathological status of RGC axons.
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