Purpose:
To detect changes in oxygen saturation of the optic nerve head in a monkey after the onset of a chronic intraocular pressure rise and to develop an early-phase glaucoma model.
Methods:
Chronic unilateral elevation of intraocular pressure in one eye of a monkey was induced with the application of argon laser energy to 180 degrees of the trabecular meshwork (50-100 µm spot size, 0.1 seconds, 1600 mW, 120 shots) in 1 session while the monkey was under general anesthesia. Using a single laser session with a lower amount of laser than was previously used led to a minimal to modest IOP elevation from 8 mmHg to 15mmHg. This pressure remained constant for the five-week period of study.We measured optic nerve head oxygen distribution in this monkey model with a hyperspectral imaging system. Spectral reference curves were obtained from a red-cell suspension prepared from blood drawn from the monkey. References were set to 0% saturation with sodium dithionate and to 97% saturation by equilibrium of room air. Saturation was read by a blood-gas analyzer with a saturation read-out, and samples were imaged in glass capillary tubes. A 100% sample was recorded from the retinal artery while the monkey was breathing of pure oxygen.
Results:
The relative saturation indices for artery, vein, superior, inferior, nasal, temporal, and cup regions of the ONH are summarized in the table.
Conclusions:
The controlled application of a lower than usual amount of laser energy has led to a minimal intraocular pressure elevation that persisted over five weeks, creating an early-phase glaucoma model. Monitoring oxygen saturation of the optic nerve head tissue and overlying retinal vessels did not show any significant change in oxygen saturation. By using the hyperspectral technique, we will be able to detect changes in oxygen consumption over time.
Keywords: blood supply • imaging/image analysis: non-clinical • retina