There has been a longstanding interest in imaging retinal ganglion cells (RGCs) because
their death causes vision loss in glaucoma, the second leading cause of
acquired blindness worldwide. Despite great efforts, no one has
successfully captured images of individual RGCs, in part because they
are nearly perfectly transparent.
Instead of imaging RGCs directly, glaucoma is currently diagnosed
by assessing the thickness of the nerve fibers projecting from the RGCs
to the brain. However, by the time retinal nerve fiber thickness has
changed detectably, a patient may have lost 100,000 RGCs or more.
‘A new method to non-invasively image the human retina, a layer of cells at the back of the eye that are essential for vision, has been developed by researchers.’
"You only have 1.2 million RGCs in the whole eye, so a loss of
100,000 is significant," said David Williams,
Dean for Research in Arts, Sciences, and Engineering. "The sooner we can catch the
loss, the better our chances of halting disease and preventing vision
Researchers at the University of Rochester Medical Center have
developed a new imaging technique that could revolutionize how eye
health and disease are assessed. The group is first to be able to make
out individual cells at the back of the eye that are implicated in
vision loss in diseases like glaucoma. They hope their new technique
could prevent vision loss via earlier diagnosis and treatment for these
In a study highlighted in the Proceedings of the National Academy of Sciences
Ethan A. Rossi, assistant professor of Ophthalmology at the
University of Pittsburgh School of Medicine, describes a new method to
non-invasively image the human retina, a layer of cells at the back of
the eye that are essential for vision.
The research group was able to distinguish individual RGCs, which bear most of the responsibility of relaying visual
information to the brain.
Rossi and his colleagues were able to see RGCs by modifying an
existing technology - confocal adaptive optics scanning light
ophthalmoscopy (AOSLO). They collected multiple images, varying the
size and location of the detector they used to gather light scattered
out of the retina for each image, and then combined those images.
technique, called multi-offset detection, was performed at the
University of Rochester Medical Center in animals as well as volunteers
with normal vision and patients with age-related macular degeneration.
Not only did this technique allow the group to visualize
individual RGCs, but structures within the cells, like nuclei, could
also be distinguished in animals. If Rossi can achieve that level of
resolution in humans, he hopes to be able to assess glaucoma before the
retinal nerve fiber thins - and even before any RGCs die - by detecting
size and structure changes in RGC cell bodies.
While RGCs were the main focus of Rossi's investigations, they
are just one type of cell that can be imaged using this new technique.
In age-related macular degeneration, cone photoreceptors that detect
color and are important for central vision are the first to die.
has been used to image cones before, but these cells were difficult to
see in areas near Drusen, fatty deposits that are the most common early
sign of the disease. Using their multi-offset technique in age-related
macular degeneration patients, Rossi was able to assess the health of
cones near Drusen and in areas where the retina had been damaged.
"This technique offers the opportunity to evaluate many cell
classes that have previously remained inaccessible to imaging in the
living eye," said Rossi. "Not only RGCs, but potentially other
translucent cell classes and cellular structures."
Rossi and his colleagues warn that their study included a small
number of volunteers and an even smaller number of age-related macular
degeneration patients. More studies will be needed to improve the
robustness of the technique and ensure their results are reproducible
before it can be widely used in the clinic.
Rossi is now setting up his
own laboratory at the University of Pittsburgh and plans to continue
working with Williams' group in studying this technique and its ability
to detect changes in retinal cells over the course of retinal diseases.