Reflectance oximetry via ICCD camera

M. Crittin et al., used the 4 Quik E ICCD camera for reflectance oximetry of the human eye. These measurement technique presupposes a camera suitable for extreme low light conditions.

a) Eye Sequence of reflectance oximetry b) Photograph of the retinal oximeter.

a) A typical set of images taken with the retinal oximeter using a ICCD camera. For the oximetry evaluation, the images at 600nm and at 569nm are used.
b) Photograph of the retinal oximeter showing the ICCD camera (A), image splitter (B) and the fundus camera (C).

Intensified cameras are a superior tool for reflectance oximetry.

This technique enables measurements of oxygen saturation in retinal vessels of the human eye.

Non-invasive optical measurements of the human eye must not use strong light sources. This condition confront the detector of these measurements with specific challenges. These low light imaging conditions need specific detector solutions which enable a good signal to noise ratio even at lowest light conditions. ICCD cameras provide superior intensified imaging with a photonic gain up to 106 and convince with an all in one head solution. Therefore, the reflectance oximetry measurements take advantage of the ICCD cameras and its most impressive performance at low light conditions.

Detection of the oxygen supply of the human eye

The retina of an human eye has a high oxygen demand. Therefore, the alteration of the oxygen supply plays an important role in retinal vascular diseases. The oxygen supply within the retina can be diagnosed by determination of the oxygen saturation in the human eye. For that reason a non-invasive measurement has numerous potential clinical applications like the diagnosis and monitoring of ocular diseases. Furthermore these measurements are essential for a better understanding of the relationship between oxygen consumption, activity, and metabolism in the retina.

Reflectance oximetry is non-invasive

The reflectance oximetry of the retina enables the non-invasive determination of the oxygen saturation. This technique is based on the fact that the light absorption by blood depends on the blood oxygen saturation. Blood absorbs different wavelength of the incoming light depending on its oxygen saturation. The oxygen saturation of the blood can then be calculated by the ratio of reflected light by different wavelengths. This means that a retinal oximeter must image the retina at multiple wavelengths.

Extreme low light conditions requires a ICCD camera

Challenging of the reflectance oximetry of the human eye is the non-invasive constraint. Since the human eye is a sensitive organ the amount of light used to image the retina is limited. Additionally, the retina has by nature a weak reflectance due to the fact that the retina uses as much light as possible for the human vision. Hence, reflectance oximetry requires a detector suitable for extreme low light conditions. The 4 Quik E intensified CCD camera allows good image quality even at extremely low light conditions. The ICCD cameras enable very good signal to noise ratios even without active cooling of the camera. Hence, intensified CCD cameras are a user-friendly tool for very low light measurements.

Title: Hemoglobin oxygen saturation (So2) in the human ocular fundus measured by reflectance oximetry: preliminary data in retinal veins
Author: M. Crittin, H. Schmidt, C. E. Riva
Institute: Laboratoire d'Optique et de Biophysique, Sion, Switzerland

Title: Functional imaging of the human papilla and peripapillary region based on flicker-induced reflectance changes
Author: M. Crittin, C. E. Riva
Institute: Laboratoire d'Optique et de Biophysique, Sion, Switzerland