There are already a number of inexpensive new devices that allow doctors in developing nations to image patients' retinas. In order to get a better look at what's going on, though, an optical coherence tomography (OCT) scanner is required – and a cheaper one of those has now also been developed.

Instead of simply taking a picture of the surface of a patient's retina, OCT scanners send light waves into the retina, constructing an internal image by analyzing how the phase of those waves has shifted upon being reflected back to the scanner. The devices perform this analysis via an integrated spectrometer, in which the light waves are guided through a W-shaped path of lenses, mirrors and diffraction slits.

Typically, the scanners are large, weighing over 60 lb (27 kg). They also incorporate precision-cut steel components, and must be designed to guard against misalignments caused by temperature changes. As a result, they're quite expensive, reportedly costing between US$50,000 and $120,000. This not only puts them out of the range of most ophthalmologists in poor countries, but even limits their usage in First World clinics.

Led by Prof. Adam Wax and his former grad student Sanghoon Kim, a team at North Carolina's Duke University set about designing an OCT scanner that was much smaller and more affordable. The resulting portable system consists of two largely 3D-printed units: the actual scanning device, and the touchscreen display module. They weigh a combined 4 lb (1.8 kg), and are expected to sell for under $15,000.

Instead of the traditional W-shaped light path, the setup utilizes one that is ring-shaped. This arrangement is said to be much more resistant to misalignment, as any significant temperature-changes cause all of the components to expand or contract in unison with one another, keeping all of the optical elements properly aligned. It also has a larger, more forgiving light detector.

When the Duke OCT scanner was used to examine both eyes of 60 patients, its retinal images were found to be 95 percent as sharp as those obtained by a traditional scanner – this is reportedly sufficient for accurate clinical diagnosis of diseases such as macular degeneration, diabetic retinopathy, and glaucoma.

It is now being commercialized through startup company Lumedica.

"There's a lot of interest from people who want to take OCT to new parts of the globe as well as to underserved populations right here in the US," says Wax. "We hope we can save a lot of people's sight by drastically increasing access to this technology."

A paper on the research was recently published in the journal Translational Vision Science & Technology.

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