The Oxymap T1
It is composed of a custom-made optical adapter and two high resolution digital cameras (1600 x 1200 square pixels) which produce quality images in a 50° field of view without sacrificing pixel resolution across the vessels.
How Does the Oxymap T1 Work?
The Oxymap T1 is installed on a conventional fundus camera which is operated as for color photography. The Oxymap T1 simultaneously acquires two images of the same area of the fundus at two different wavelengths of light. One of the two wavelengths is sensitive to oxygen saturation, i.e. the light absorbance changes with the oxygen saturation, while the other is insensitive to oxygen saturation and is used to calibrate the light intensity.
The two spectral images are automatically processed by the Oxymap Analyzer software. Oxymap Analyzer detects blood vessels and estimates the light absorbance (optical density) at each point along the vessels at each wavelength.
The ratio of the optical densities (optical density ratio or ODR) has been shown to be linearly related to hemoglobin oxygen saturation.1 The parameters for the linear equation were calibrated so that the average oxygen saturation of arterioles and venules was 92,2% and 57,9% respectively, for a group of normal subjects.2
The retinal vessel width is evaluated based on average cross sections of vessel segments which are detected by the vessel detection algorithm.
1. Beach JM, Schwenzer K, Srinivas S, Kim D, Tiedeman JS. Oximetry of retinal vessels by dual-wavelength fundus imaging: calibration and influence of pigmentation. J Appl Physiol. 1999 Feb;86(2):748-58.
2. Schweitzer D, Hammer M, Kraft J, et al. In vivo measurement of the oxygen saturation of retinal vessels in healthy volunteers. IEEE Trans Biomed Eng. 1999;46:1454–1465.