New imaging technique may help prevent vision loss

Scientists have developed a new non-invasive retinal imaging technique that could help prevent the onset of vision loss in diseases like glaucoma - the second leading cause of acquired blindness worldwide.
Researchers at the University of Rochester Medical Centre in the US hope their new technique could prevent vision loss via earlier diagnosis and treatment for these diseases.
The method can non-invasively image the human retina, a layer of cells at the back of the eye that are essential for vision.
The group led by David Williams from the University of Rochester was able to distinguish individual retinal ganglion cells (RGCs) which bear most of the responsibility of relaying visual information to the brain.

There has been a longstanding interest in imaging 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 fibre thickness has changed detectably, a patient may have lost 100,000 RGCs or more.
"You only have 1.2 million RGCs in the whole eye, so a loss of 100,000 is significant. The sooner we can catch the loss, the better our chances of halting disease and preventing vision loss," said Williams.

Ethan A Rossi, assistant professor at the University of Pittsburgh School of Medicine in the US 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.
The technique, called multi-offset detection, was performed 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 visualise 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.
The study was published in the journal PNAS.