Using Near Infrared Light to Detect Hypoxia in Retinal Images

Acute hypoxia poses a serious risk in military aviation because it can lead to impaired performance of safety-critical tasks. Early detection of hypoxia is therefore critical. Oxygen saturation (Spo2) of the retinal blood vessels may serve as a surrogate biomarker for brain hypoxia. This study investigates the feasibility of detecting hypoxia through retinal imaging in the near-infrared (NIR) spectrum, which does not interfere with the pilot's vision.

There were 12 subjects who participated in a hypobaric flight simulation to lower systemic Spo2. Retinal images were captured using a dual-wavelength NIR fundus camera, while Spo2 was measured via fingertip pulse oximetry. The optical density (OD) of retinal blood vessels was extracted from the images at both wavelengths. It was hypothesized that the ratio of vessel OD between the two wavelengths increases with rising Spo2.

Measured Spo2 was compared with the calculated OD ratio. No correlation was found between the OD ratio and Spo2.

NIR retinal imaging appears to be unsuitable for accurate hypoxia detection within an acceptable ±4% error margin using our imaging protocol. This is mainly due to the low contrast of blood vessels in the NIR wavelength region, along with limited imaging repeatability resulting from realignment and refocusing steps in the imaging protocol. These factors have a larger distorting effect on the images than the subtle OD ratio changes related to varying Spo2. Bekkers A, Zoutenbier V, Bussink P, Groen E, Kuijf H, Amelink A. Using near infrared light to detect hypoxia in retinal images. Aerosp Med Hum Perform. 2026; 97(2):111-115.