Adaptive Optics
The Lowy Medical Research Institute collaborates with a group of extramural investigators who specialize in using adaptive optics to study the retina. “Adaptive optics,” in this case, refers to ophthalmoscopes that have been specially modified to allow scientists to take remarkably clear pictures of the living retina. Individual light sensing cells in the back of the eye, or photoreceptors, can be photographed using this technique.
The LMRI Adaptive Optics Group examines the retinas of MacTel patients to learn how photoreceptors are affected by the disease. The Adaptive Optics Group has made several important observations that have changed the understanding of MacTel.
When a retina affected by MacTel is imaged with adaptive optics, the resulting image typically shows a patch of darkness in the center of the retina. This is referred to as the MacTel lesion, and it is where vision loss occurs due to MacTel. Researchers can’t see photoreceptors in the lesion, though the cells would be there in a healthy eye. It was thought that the photoreceptors in the MacTel lesion were dead, because they could not be imaged. New research using adaptive optics suggests that this is not necessarily the case.
(Left) Fluorescein angiogram of a MacTel retina shows leakage and irregular vasculature temporal to the fovea, typical for this disease. (Right) Same retina, imaged by OCT. OCT en face view of the inner/outer segment photoreceptor junctions shows a disruption of photoreceptors in the foveal region. Images courtesy of Dr. Roorda.
Same retina as above. Adaptive optics scanning laser ophthalmoscope overlay images show photoreceptors throughout much of the image, except in the lesion. Within the lesion, hexagonal RPE cells can be seen (click to zoom). The white spot shows the point of fixation for the individual. Right, retinal sensitivity thresholds (microperimetry) at targeted locations overlaid onto the AOSLO image. This shows that while cones can’t be imaged, there is some remaining function in the lesion. Images courtesy of Dr. Roorda.
Complimentary approaches provide clues that photoreceptors within the MacTel lesion are present and alive, and may retain some function. One of these approaches pairs an ophthalmoscope fitted with adaptive optics and microperimetry. Results are shown in the images above. Microperimetry measures the sensitivity of photoreceptors to light (a lower number indicates higher sensitivity). Surprisingly, there are light-sensitive photoreceptors in the lesions of MacTel eyes. This indicates that cones are most likely present, but they are not reflecting light properly. This finding offers hope for functional recovery of diseased cones in MacTel. This research comes from Dr. Austin Roorda’s lab in Berkeley, CA.
The other approach uses an ophthalmoscope fitted with adaptive optics, along with extra light detectors, known as split-detectors. This research comes from Dr. Joseph Carroll’s group in Milwaukee, Wisconsin. When the information from such imaging devices is processed, the images show photoreceptors in the lesion. The photoreceptors weren’t previously detected because they are not reflecting light in the same way as a normal, healthy photoreceptor. It is possible that the photoreceptors are missing their outer segments, or that their outer segments aren’t properly oriented. These findings agree with what is suggested by Dr. Roorda’s findings, described above.