Abstract
Purpose :
The optic nerve head (ONH) minimum rim width (MRW) thins prior to retinal nerve fiber layer thickness (RNFLT) in glaucoma. MRW is also sensitive to intraocular pressure (IOP), thinning with IOP elevation and thickening with IOP lowering. The goal of this study was to quantify the rate and extent of MRW thickening with IOP reduction in non-human primate (NHP) experimental glaucoma eyes.
Methods :
The right eyes of 3 NHPs were studied at three stages: 1) baseline, 2) early (< 5% RNFLT change), and 3) mild (5-25% RNFLT change) neuropathy. For each experiment, the anterior chamber was cannulated and IOP controlled via a closed-loop system with a pressure transducer and syringe pump, and radial ONH optical coherence tomography (OCT) scans were acquired at 5 min intervals. Two baseline sessions quantified MRW over a 2-hr period of 10 mmHg IOP, following 2-hr exposure to 25 or 40 mmHg IOP. After laser scarring of the trabecular meshwork, animals were monitored every 2 weeks with OCT until they reached early and mild stages. At each stage, IOP was set to the measured pre-cannulation IOP for 45 min, then 10 mmHg for 2 hrs. MRW, Bruch’s membrane (BM) opening (BMO) area, BMO position referenced to a 12-deg BM plane, and anterior lamina cribrosa surface depth (ALCSD) referenced to the BMO were quantified from OCT scans. MRW data were fit with exponential rise to maximum functions. Values are expressed as median (range).
Results :
At all stages, MRW gradually thickened with IOP lowering. MRW recovery at baseline was greater for 40 mmHg (19.0 µm [15.6-23.6 µm]) than 25 mmHg (12.5 µm [7.1-13.3 µm]). While MRW recovery at early stage glaucoma (16.0 µm [13.9-25.8 µm]) was similar to baseline, greater recovery occurred in mild glaucoma (43.2 µm [17.8-46.6 µm]). Likewise, the BMO moved more anteriorly in mild glaucoma (35.6 µm [23.1-72.0 µm]) compared with healthy (25mmHg: 15.0 µm [10.9-18.1 µm]; 40mmHg: 19.2 µm [15.2-21.8 µm]) or early glaucoma eyes (20.4 µm [14.1-31.3 µm]). MRW half-life, BMO area, and ALCSD did not show consistent changes with disease.
Conclusions :
Mild glaucoma eyes exhibit greater MRW thickening and more anterior BMO displacement with IOP lowering than healthy or early glaucoma eyes. Differences in ONH response to IOP with disease stage likely reflect tissue remodeling. It is possible that ONH morphological response to IOP may be useful for assessing disease stage and/or susceptibility to disease.
This is a 2020 ARVO Annual Meeting abstract.