Frequently Asked Questions
Is the oximeter certified for clinical use?
Not yet.
Can the oximeter be used to take color fundus photographs or to do fluorescein angiography?
The oximeter is built on the Topcon TRC-50DX fundus camera. The specialized optics needed for oximetry are attached to the top port of the fundus camera. The lower port can therefore be used to attach a color digital camera for color fundus photography or fluorescein angiography. The digital color camera is an optional accessory.
What is the light source used to illuminate the fundus for oximetry measurements?
The light sources of the fundus camera are used to illuminate the fundus. A halogen lamp is used for observation and a xenon flash for photography. An additional filter is provided by Oxymap with the oximeter to decrease unnecessary exposure to light. This filter passes wavelengths from 545 nm to 615 nm and thus filters ultraviolet and infrared radiations.
What wavelengths are used for oximetry measurements?
570 nm and 600 nm are used. Two light filters select the measurement wavelengths, one for each digital camera. The centre wavelengths of the filters are 570 nm and 600 nm and the full width at half maximum is 5 nm.
Why are 570 nm and 600 nm used as measurement wavelengths?
These wavelengths are selected based on the absorbance of hemoglobin: to do oximetry measurements, one oxygen sensitive wavelength and one oxygen insensitive wavelength are used. Oxygenated and deoxygenated hemoglobin have the same light absorbance at 570 nm but not at 600 nm. The oxygen insensitive wavelength serves as a reference in the calculation of hemoglobin oxygen saturation.
How long does it take to process an oximetry image?
The color-coded map of the oxygen saturation is generated automatically in less than one minute (the exact time depends on computer power). New images can be acquired while image processing is ongoing.
What is the spatial resolution of the oximetry images?
Full camera sensor size is 1600 pixels x 1200 pixels. While operating the fundus camera in the 50° field of view, the first degree and second degree vessels are 10 to 20 pixels across. The area of the retina which is covered by the oximeter can be seen on this image (50° field of view):
How is the vessel width measured?
The vessel width is evaluated based on average cross sections of vessel segments which are detected by Oxymap's vessel detection algorithm. Vessel width is given in terms of pixel units.
