Saturday, 25 October 2014
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Far-sighted

Biomedical engineers hope to save the sight of millions by pushing the boundaries of an established imaging device.

They aim to use optical coherence tomography (OCT) to detect the very first evidence of glaucoma — an eye condition that, because it progresses so stealthily, leads to blindness.

'Glaucoma kills the optic nerve — once it's gone, we can't bring vision back,' said physician and biomedical engineering professor Henry Grady Rylander, who is leading the five-year research project at the University of Texas, Austin.

The trouble is that symptoms are very difficult to spot, and often the disease is detected too late, after substantial damage has been done. Also, the causes are not always clear. They are thought to include poor circulation and a build-up of fluid in the eye that puts pressure on vital cells.

Rylander's team has won £1.3m of funding from the US National Eye Institute to see if OCT can reveal in greater detail changes in the internal structures within the extensions of ganglion nerve cells. At the back of the eye, these carry visual information to the brain, and their gradual loss caused by glaucoma limits and eventually destroys vision. Microtubules in the isolated extensions are thought to disappear early in glaucoma. 'Microtubules are probably one of the first structures to go, and if you could discover a non-invasive way to measure their disease-related changes, you could come up with ways to protect them from dying,' said Rylander.

OCT is already used in ophthalmic work, to evaluate conditions that affect the retina, like macular degeneration. The system images eye tissue by bouncing broadband light from either super bright LEDs or lasers off it, similar to the way that ultrasound produces images with soundwaves. It is non-invasive with sub-micrometre resolution, but conventional devices can only penetrate tissue by up to 3mm.

The light from an OCT system is broken into two branches — one to penetrate the sample and the other to be a reference. The combination of backscattered light from the sample branch, and reference light from the reference branch causes an interference pattern. A cross-section image is created by combining several interference patterns.

The researchers will have to modify the OCT equipment to achieve the penetration and resolution needed to monitor changes in the microtubules. Examinations of the eyes of animals will be followed in 2009 with assessments of 40 human volunteers who suffer from glaucoma. Rylander's ultimate goal is to have the glaucoma examination available for ophthalmologists within 10 years.


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