In the 1990s, astronomers pioneered a new technology—called adaptive optics, or AO—to help reduce distortion caused by the atmosphere when they looked at stars and planets through Earth-stationed telescopes. Now, vision researchers are using the same technology to reduce distortion caused by imperfections in the eye’s cornea and lens when using light-based devices to look at the retina, the layer of light-sensitive tissue in the back of the eye. The retina houses rod and cone photoreceptors, which are specialized neuronal cells that convert light that enters the eye into electrical signals sent to the brain.
The National Eye Institute recently sponsored a workshop to explore how AO could be incorporated into clinical devices, giving more researchers and eventually eye care professionals access to this powerful technology that can noninvasively capture images of cells 20 times smaller than the diameter of a human hair.
Retinal images taken with scanning laser opththalmoscopy without (l) and with (r) adaptive optics (AO); AO reveals individual photoreceptors.
Photos: Joseph Carroll and Alfredo Dubra, Medical College of Wisconsin
For applications in the eye, AO works by aiming a dim beam of light toward the retina and then measuring distortion in the light reflected with a device called a wavefront sensor. Information collected by this sensor is read by a computer-controlled mirror that corrects the distortion before the light is viewed by the user. AO technology has been incorporated into a variety of imaging techniques, including optical coherence tomography and scanning laser ophthalmoscopy. The results are images with unprecedented sharpness.
“With adaptive optics, some of these high-resolution imaging techniques may provide us with an opportunity to identify early manifestations of disease that are not obvious with standard clinical tools,” said Dr. Jacque Duncan, director of the University of California, San Francisco, retinal degenerations clinic, who helped plan the workshop. Such diseases include glaucoma, age-related macular degeneration and diabetic retinopathy—the three most common causes of vision loss among Americans.
The Clinical Application of Adaptive Optics Retinal Imaging incubator meeting, held at the headquarters of the Optical Society of America in Washington, D.C., explored key design parameters for clinical AO devices, including minimum resolution, ability to integrate with other imaging modalities, cost, portability and ease-of-use. The meeting heard perspectives from scientists and clinicians with diverse interests and requirements. In addition, representatives from Canon, Nidek, Topcon and other companies provided insight from a device manufacturer’s perspective.
Workshop participants identified potential FDA requirements for AO devices used in standard clinical care and for use in clinical trials, which AO imaging could vastly accelerate. Many degenerative eye diseases, such as retinitis pigmentosa, cause vision loss over a period of many years due to a loss of photoreceptor cells. Subtle changes in vision are difficult to measure. AO would allow researchers to easily count rods and cones, providing a more objective means to evaluate a new therapy’s effectiveness.
Participants identified several aspects that must be addressed before AO devices can be successfully integrated into clinical settings, including the need for standardized calibration protocols, defined metrics to gauge image quality and a reference database of “normal” samples. Several working groups were created at the meeting to address these aspects.
Dr. Matt McMahon, NEI senior advisor for translational research, said that standard and joint grant funding mechanisms and challenge prize competitions would help drive innovation in areas where AO technology is lagging, such as computer algorithms to automate photoreceptor cell counting.