Oximetry with the Optos200Tx in Diabetic Retinopathy

Abstract

Purpose: Changes in retinal vascular oxygenation have been reported in diabetic patients (Pts) with dedicated oximetry equipment. Oximetry has also been performed in healthy subjects and patients with retinal vascular occlusions with the Optos200Tx (Optos), a commercially available scanning laser ophthalmoscope. We tested the hypothesis that Optos could be used to reveal retina vascular oxygen saturation changes in diabetic retinopathy (DR), including effects of anti-VEGF treatment.

Methods: Oximetry was performed in 10 eyes of 10 normal subjects (Nls)(age, 49±12 years) and 17 eyes (9 NPDR, 8 PDR) of 17 Pts (age, 63±14 years). Imaging was repeated (approximately 6 weeks apart) in 5 Nls and 11 Pts (4 before and after anti-VEGF treatment). Optos images were acquired at 532 nm and 633 nm. A customized software program was developed to measure retinal vascular caliber and optical density (OD), and calculate optical density ratios (ODR) according to ODR = OD₆₃₃/ OD₅₃₂. Arterial (SO_2A) and venous (SO_2V) oxygen saturations were obtained using an ODR to SO₂ calibration. A minimum of 6 arterial and 6 venous measurements per eye was used to derive vessel caliber, SO_2A and SO_2V. Oxygen extraction fraction (OEF) was calculated as (SO_2A- SO_2V)/ SO_2A. Data were analyzed with student’s t test and ANOVA.

Results: SO_2A were 92.0±13.5 (mean and SD) and 100.8±13.2 % in Nls and Pts, respectively (P=0.11). SO_2V were 57.8±18.7 and 72.8±11.9 % in Nls and Pts, respectively (P=0.017). SO_2A- SO_2V and OEF did not differ statistically between Nls and Pts. No differences in vascular calibers were found between Nls and Pts. In Pts having anti-VEGF treatment SO_2A, SO_2A- SO_2V, and OEF were 97.5±11.0%, 32.8±9.1% and 0.34±0.08 at baseline. These decreased to 90.1±12.6%, 19.7±4.5% and 0.22±0.05 after treatment (all P˂0.05). No significant changes in these factors over time were seen in Nls or in Pts not receiving treatment.

Conclusions: Oximetry with the widely available Optos200Tx instrument detected retinal vascular SO₂ changes in DR and thus may prove useful in managing Pts, especially for monitoring anti-VEGF treatment outcomes.