Frequently Asked Questions
- Where can I get the latest documentation for the Oxymap T1?
- Where can I get an example analysis protocol and instructions on how to copy data from the application into Excel?
- Is the Oxymap T1 certified for clinical use?
- How can the oxygen saturation be more than 100%?
- Can the Oxymap T1 be used to take color fundus photographs or to do fluorescein angiography?
- Why are my analysis results different from average values?
- What do I do when the connection to the cameras is lost?
- Why should I choose the new vessel detection algorithm(v2)?
- What is the light source used to illuminate the fundus for oximetry measurements?
- What wavelengths are used for oximetry measurements?
- Why are 570 nm and 600 nm used as measurement wavelengths?
- How long does it take to process an oximetry image?
- What is the spatial resolution of the oximetry images?
- How is the vessel width measured?
- Is it difficult to operate the Oxymap T1?
Where can I get the latest documentation for the Oxymap T1?
You can get it at this page.
Where can I get an example analysis protocol and instructions on how to copy data from the application into Excel?
You can download a .zip file containing text and video instructions at this page.
Is the Oxymap T1 certified for clinical use?
The Oxymap T1 is now CE marked since early September 2013 but not yet intended to aid in diagnosing of diseases or treatment of patients. Oxymap T1 has been installed outside of Europe as an investigational device in several university hospitals in the United States, Asia and Australia.
How can the oxygen saturation be more than 100%?
Readings above 100% do not make a physiological sense but the reason for them is that the device is only capable of delivering ”relative” results but not absolute measurements of oxygen saturation. The calibration procedure is described in the manual and the calibration is set so that mean saturation for arterioles in young healthy individuals should be close to 92.2% and mean saturation for venules close to 57.9%. Do not worry much about occasional >100% in individual vessel values for individual cases if the mean is “normal”.
Can the Oxymap T1 be used to take color fundus photographs or to do fluorescein angiography?
The Oxymap T1 is an add-on for 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.
Why are my analysis results different from average values?
There are several possible explanations for unexpected readings. Do not rule out the possibility that your results may have physiological explanations. Retinal oximetry is a new field of science and our understanding retinal oxygenation is still being improved. Artificial or confounding factors to your study may include:
- The image quality might be poor. Cataract or interference from eye lashes or poorly dilated pupils can make a large difference. The images must have good contrast and the illumination of the retina must be even.
- The alignment of the image may make a difference, see the paper by Palsson et al in IOVS.
- Different protocol used for selecting vessel segments. Not everyone use the same protocol and thus it can give different values.
- The degree of pigmentation can influence the results.
- Low or nonstandard illumination, make sure you choose sufficient flash settings e.g. 50Ws.
- The age might affect the outcome. Studies show slightly less oxygen saturation in the venules in older people (but the difference in arterioles is very small, if any). See Geirsdottir et al.
What do I do when the connection to the cameras is lost?
Make sure you start up the system in the right order. Before you startup the Oxymap Analyzer (the software) you need to turn on the Topcon fundus camera using the switch button on the side of the camera and the Oximap Digitizer (the hardware) by turning on the master switch on the control box.
Make sure the Firewire cables and other cables are firmly connected. You should be able to see both digital cameras if you click on hardware eject icon (in the lower right corner of the screen) to make sure the cameras are recognised by the computer.
If you are still having problems please contact us at firstname.lastname@example.org.
Why should I choose the new vessel detection algorithm(v2)?
The new vessel detection algorithm (v2) has been improved with new the digital image processing filters and optimized the vessel classification algorithm using a much larger training data set acquired with the Oxymap T1. This has considerably improved the performance of the vessel detection.
If you are currently using the old vessel detection algorithm (v1) and choose to start using the new one, statistical comparison of results between your current data and new data may be invalid.
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 of the eye. A halogen lamp is used for observation and a xenon flash for photography. An additional filter is provided by Oxymap with the Oxymap T1 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?
The 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.
Is it difficult to operate the Oxymap T1?
The Oxymap T1 in installed on top of a fundus camera and therefore operates like normal fundus photography. It takes a little practice to acquire good-quality retinal images. This short guide gives tips on how to acquire good images. The Ophthalmic Photographers’ Society has also useful information about image focus and how to adjust the eyepiece.