David Bragason

Retinal vessel oxygen saturation and vessel diameter in retinitis pigmentosa.

To assess retinal vessel oxygen saturation and retinal vessel diameter in retinitis pigmentosa.

Retinal Oximetry Imaging in Alzheimer's Disease

BACKGROUND Structural and physiological abnormalities have been reported in the retina in Alzheimers disease (AD). Retinal oximetry detects changes in retinal oxygen metabolism in many eye diseases, where structural changes are seen. OBJECTIVE To compare oxygen saturation in retinal blood vessels in patients with AD and a healthy cohort. METHODS Oxygen saturation of hemoglobin was measured in retinal blood vessels, using imaging with spectrophotometric noninvasive retinal oximeter. 18 individuals with mild to moderate dementia of the Alzheimer-type (stage 3-5 according to the Global Deterioration Scale) and 18 healthy subjects underwent retinal oximetry in a case control study. RESULTS Retinal oxygen saturation in arterioles and venules in patients with moderate AD was significantly elevated compared to healthy individuals. Retinal arterioles have 94.2 ± 5.4% oxygen saturation in moderate AD compared with 90.5 ± 3.1% in healthy subjects (mean ± SD, n = 10, p = 0.028). Retinal venules were 51.9 ± 6.0% saturated in moderate AD compared with 49.7 ± 7.0% in healthy subjects (mean ± SD, n = 10, p = 0.02). CONCLUSION This is the first study of retinal oxygen metabolism in any central nervous system disease. It discovers abnormalities in retinal oxygen metabolism in AD. The findings are similar to those seen in age-related macular degeneration and diabetic retinopathy. Noninvasive retinal oximetry may offer new insights into pathophysiology of AD. Further studies are needed to confirm and expand these findings.

Venous oxygen saturation is reduced and variable in central retinal vein occlusion

Purpose To estimate the presence and variability of retinal hypoxia in patients with central retinal vein occlusion (CRVO).

Retinal oximetry measures systemic hypoxia in central nervous system vessels in chronic obstructive pulmonary disease

Background Determination of the blood oxyhemoglobin saturation in the retinal vessels of the eye can be achieved through spectrophotometric retinal oximetry which provides access to the state of oxyhemoglobin saturation in the central nervous system circulation. The purpose of this study was to test the capability of the Oxymap T1 oximeter to detect systemic hypoxemia and the effect of supplemental oxygen on retinal vessel oxyhemoglobin saturation. Methods Oxygen saturation of hemoglobin in retinal arterioles and venules was measured in 11 subjects with severe chronic obstructive pulmonary disease (COPD) on long term oxygen therapy. Measurements were made with and without their daily supplemental oxygen. Eleven healthy age and gender matched subjects were measured during ambient air breathing for comparison of oxyhemoglobin saturation in retinal arterioles and venules. Retinal arteriolar oxyhemoglobin saturation in COPD subjects inspiring ambient air was compared with finger pulse oximetry and blood samples from radial artery. Results COPD subjects had significantly lower oxyhemoglobin saturation during ambient air breathing than healthy controls in both retinal arterioles (87.2%±4.9% vs. 93.4%±4.3%, p = 0.02; n = 11) and venules (45.0%±10.3% vs. 55.2%±5.5%, p = 0.01). Administration of their prescribed supplemental oxygen increased oxyhemoglobin saturation in retinal arterioles (87.2%±4.9% to 89.5%±6.0%, p = 0.02) but not in venules (45.0%±10.3% to 46.7%±12.8%, p = 0.3). Retinal oximetry values were slightly lower than radial artery blood values (mean percentage points difference = -5.0±5.4, 95% CI: -15.68 to 5.67) and finger pulse oximetry values (-3.1±5.5, 95% CI: -14.05 to 7.84). Conclusions The noninvasive Oxymap T1 retinal oximetry detects hypoxemia in central nervous system vessels in patients with severe COPD compared with healthy controls. The instrument is sensitive to changes in oxygen breathing but displays slightly lower measures than finger pulse oximetry or radial artery measures. With further technological improvement, retinal oximetry may offer noninvasive “on-line” measurement of oxygen levels in central circulation in general anesthesia and critically ill patients.

Response to the letter to the editor: Venous oxygen saturation is reduced and variable in central retinal vein occlusion

Dear editor; We want to thank Yolcu et al. for their insightful letter about our study. We fully agree with their opinion on pertinence for oximetric results of central retinal vein occlusion (CRVO) eyes with and without macular edema or retinal ischemia to be compared with each other. We also agree that its results can be compared with fluorescein angiography and optical coherence tomography findings in different sectors of the retinal fundus. This is important in order to explore the clinical utility of the oximeter. Our study [1] demonstrates variable retinal hypoxia in CRVO eyes that in general seems to get better with time, treatment and improving clinical symptoms. Our preliminary findings suggest a correlation between retinal oximeter measurements and clinical signs and symptoms. Hypoxia measurements in retinal venules were consistent with capillary nonperfusion on fluorescein angiography [1]. We agree that assessing patients by optical coherence tomography and fluorescein angiography and comparing with retinal oximeter measurements will provide valuable information for the pathogenesis and management of CRVO. We have started a multicenter study in order to answer the aforementioned questions and pursue the clinical utility of retinal oximetry in CRVO.