Normal limits of retinal oximetry and retinal venous oxygen saturation in atrophic diseases

Abstract

Purpose : Disturbances in retinal metabolism have been detected in atrophic diseases such as glaucoma and retinitis pigmentosa (RP). There have been speculations that metabolic imaging of the retina could be helpful in monitoring these diseases and perhaps help with diagnosis. The aim of the project was to establish normal limits for retinal oximetry and test whether results from patients with glaucoma and RP fit within these limits.

Methods : Retinal vessel oxygen saturation was measured in 89 healthy individuals, 78 patients with primary open angle glaucoma and normal tension glaucoma and 10 patients with RP. Measurements were performed with a spectrophotometric retinal oximeter, Oxymap T1. The oximeter simultaneously acquires two images of the same area of the fundus at two different wavelengths of light, 600nm and 570nm. A specialized software automatically measures light absorbance of retinal vessels and calculates oxygen saturation.

Results : In the healthy group, 5% of the venous saturation values were above 64%. Six glaucoma patients (8%) and two RP patients (20%) had venous saturation higher than 64%. Mean venular oxygen saturation was higher in advanced glaucoma (MD≥10dB) compared with healthy individuals (57.9%±5.5% vs. 53.8%±6.4%, p=0.007, mean±SD). Venous saturation in RP was also higher than in healthy individuals (58.0%±6.2% vs. 53.8%±6.4%, p=0.05). The visual field mean defect in the six glaucoma patients outside the 95% limit for healthy individuals ranged from -1dB (good visual field) to 26.7dB (advanced visual field).

Conclusions : Most of the patients in both groups (glaucoma and RP) were within normal limits for venular oxygen saturation, even though glaucoma patients with advanced visual field damage and RP patients have increased venular oxygen saturation compared with healthy individuals.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.

 

Table. Mean retinal vessel oxygen saturation in healthy individuals, glaucoma and RP patients.

 

Figure. The relative frequency of venous oxygen saturation levels in healthy individuals, glaucoma patients and RP patients.