Abstract
Purpose :
The potential for tissue oxygenation in the retina is affected by several factors, such as the decrease in capillary density in eyes with diabetes. Vessel diameter also affects the assessment of oxygenation, with measurements improved by the delineation of the wall vs. lumen. We are developing metrics of tissue oxygenation by combining measurements from three retinal imaging modalities.
Methods :
We imaged retinal arterioles and surrounding capillaries of 3 subjects, ages 27, 29, and 30 yr. Subjects were selected without high myopia to minimize differences in retinal distances and thickness due to axial length. Images with a point scanning adaptive optics scanning laser ophthalmoscope (AOSLO) were collected at .93 um/pixel at 780 and 815 nm. The same locations were imaged at 1.17 um/pixel with a pseudo-line scanning adaptive optics digital light ophthalmoscope (AO-DLO) using LED illumination with center wavelengths of 630 and 540 nm. A variety of confocal apertures were used with both AO devices to a) visualize vessel walls vs. lumen to obtain accurate vessel widths or b) emphasize reflectivity off flowing particles vs. absorption in the arterioles for motion mapping for capillary density. OCT-A (Heidelberg, Spectralis) was used to provide particle motion maps of the arterioles and adjacent capillaries. Distances between capillaries and the arterioles and lumen widths were computed manually in the posterior pole (Photoshop). The light absorbance (log scale) was measured using bright- and dark-field AO-DLO imaging at 630 and 540nm illumination. The optical density ratio, proportional to oxygen saturation, was calculated as the ratio of the measured light absorbances.
Results :
Particle motion was seen at all wavelengths tested. The average width of the arteriole lumens were 68±5, 69±3, and 53±2 um, with a wall:lumen ratio of 0.265, 0.688, and 0.781, with AOSLO. In the same region, the distance from the lumen to the nearest capillary loop was 59±21, 50±17, and 55±15 um with AOSLO and 53±16, 51±20, and 52±15 um for OCT-A. As expected, the arterial light absorbance was greater for green vs. red illumination in all subjects. Optical density ratio depended on aperture condition, e.g. in 1 subject varying from -0.166 to 0.160.
Conclusions :
Several metrics of tissue oxygenation were evaluated using AOSLO, AO-DLO and OCT-A technology that may be pertinent to early diagnosis and careful monitoring of retinal disease.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.