Early morphological changes in non–human primate eyes with laser–induced ocular hypertension assessed with ultrahigh–resolution Optical Coherence Tomography, Scanning Laser Polarimetry and Scanning Laser Tomography.

Abstract

Abstract: : Purpose:To study early changes in retinal morphology in cynomolgous monkey eyes after unilateral induction of ocular hypertension (OHT). To assess and compare morphological measurements acquired with ultrahigh–resolution optical coherence tomography (uhrOCT), scanning laser polarimetry (SLP) and scanning laser tomography (SLT). Methods:OHT was induced unilaterally in 6 cynomolgous monkeys by photocoagulation of the trabeculum. 3 baseline experiments were performed prior to laser surgery. After surgery, study days were scheduled every 2–3 weeks over 3–6 months. On each study day IOP, uhrOCT, SLP and SLT measurements were performed in both eyes. IOP was measured 4 times during each experiment with a Tono–Pen. Using uhrOCT, horizontal and vertical cross–sectional images of the macula and optic nerve head (ONH) with approx. 3 µm axial resolution were obtained. Several circular scans along the parapapillary area with increasing diameter centered at the ONH were acquired. Thickness of the nerve fiber layer (NFL)as well as intraretinal layers were calculated. A GDx VCC system (Laser Diagnostic Technology) was used to acquire NFL thickness maps. Cornea compensation was performed for each measurement separately. Confocal SLT (Heidelberg Retina Tomograph, Heidelberg Engineering) was utilized to acquire focal image sequences of the ONH. Results: Baseline experiments showed a good reproducibility for all measurement systems assessing retinal morphology and topography. After laser surgery, IOP developed differently in different monkeys. Two animals displayed a stable increase in IOP of 20–35 mmHg. These monkeys showed marked changes in ONH topography already at day 20 post surgery with a pronounced cupping as delineated by uhrOCT and SLT measurements. The GDx also detected a reduction of NFL thickness already at day 20 and progressing subsequently. Three animals showed only sporadic and/or a mild increase in IOP of 10–15 mmHg. Morphological changes could also be evidenced with the employed techniques in these animals, but to a much lesser extend. Conclusions: Changes in retinal morphology can be detected at very early stages after induction of ocular hypertension in the non–human primate model of glaucoma. These changes can consistently be observed with all 3 techniques utilized.

Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • optic disc • nerve fiber layer