Adaptive Optics Sees Eye Rod Cells Clearly
Adaptive Optics (AO), the technology used by astronomers to study distant stars and galaxies clear of distortion has been used by scientists to study the cellular structure of the living eye, clear of the distortion posed by the outer eye. The researchers, from the University of Rochester, Marquette University, and the Medical College of Wisconsin, had to improve the design of non-invasive AO imaging systems. They did just that, pushing the resolution of AO to nearly 2 microns (1/1,000 of a millimeter), which is the approximate diameter of a single rod in the human eye.
There are two types of photoreceptor cells in the eye, rods and cones. Using their AO system with the higher resolution the researchers were able to clearly view even the smallest cone cells which are found at the center of the retina (in the foveal center.) The researchers also report that this is the first time that rods have been clearly and directly imaged in vivo (within a living eye).
The research, published in papers in the Optical Society’s journal Biomedical Optics Express, is significant because according to the researchers the ability to see the cells you are trying to work on is a critical step in the process of restoring a patient’s damaged vision. Retinal disease can be difficult to detect, and is often to the point where significant cellular damage has already taken place by the time treatment is attempted. Many of the eye diseases that are more likely to be treatable affect the rods, therefore this imaging technique could prove to be very useful.
The use of AO for studying the eye isn’t a novel concept. The premise behind AO lies in astronomy, where the technology is used to correct the blurring effect of the Earth’s atmosphere by using a reference point (a bright star), which is monitored and used to create a mirror image with an exact but opposite distortion to the effects of the atmosphere. Ultimately, this results in images with significantly higher resolution.
This time-tested technology was first implemented in optics in the late 1990’s, because similar to light bending and becoming distorted as it passes through the atmosphere, light traveling through the eye is also subject to bending and distortion. This makes medical imaging of the eye extremely difficult. Early AO systems for the eye were effective at imaging cone cells, but without a higher resolution were not capable of capturing clear, contiguous images of rods, which are smaller than cones, and outnumber cones in the retina 20-1.
The design breakthrough that improved the AO imaging system so that it could capture adequate views of the rod cells was a simple fix. The spherical mirrors that act as lenses in the instrument were folded into a 3-D structure, which was enough to make the instrument capable of capturing the contiguous rod mosaic and the entire cone mosaic in the foveal center.
According to the researchers, in addition to developing their design for a widely available clinical model, the next step for AO technology is teaching colleagues to interpret AO images. The researchers predict that in the next 5-10 years, high resolution AO systems will be routinely used to help doctors look into patients’ eyes with enough precision and clarity to view individual rods. This would vastly improve doctors’ ability to provide early intervention for retina disease, and allow the state of individual cells in response to treatments to be easily monitored.
(via Science Direct)