Low-cost OCT scanner promises to save eyesight

A low-cost, portable optical coherence tomography (OCT) scanner could bring the sight-saving technology to underserved regions in the US and further afield.

OCT scanner
OCT system is 15 times lighter and smaller than current commercial systems (Image: Adam Wax, Duke University)

Thanks to a redesigned, 3D-printed spectrometer, the scanner is 15 times lighter and smaller than current commercial systems and is made from parts costing less than a tenth the retail price of commercial systems.

In its first clinical trial, the new OCT scanner produced images of 120 retinas that were said to be 95 per cent as sharp as those taken by current commercial systems. The results of the work carried out by biomedical engineers at Duke University, North Carolina, appear online in Translational Vision Science & Technology.

OCT imaging has become the standard of care for the diagnosis of many retinal diseases including macular degeneration and diabetic retinopathy. However, OCT is rarely included as part of a standard screening exam since the machines are expensive.

"The key to preventing blindness is early detection," said Adam Wax, professor of biomedical engineering at Duke. "Our goal is to make OCT drastically less expensive so more clinics can afford the devices, especially in global health settings."

According to Duke, OCT is the optical analogue of ultrasound, which sends sound waves into tissues and measures how long they take to come back. To time the light waves bouncing back from the tissue being scanned, OCT devices use a spectrometer to determine how much their phase has shifted compared to identical light waves that have travelled the same distance but have not interacted with tissue.

The primary technology enabling the latest OCT device is a spectrometer designed by Wax and his former graduate student Sanghoon Kim. Traditional spectrometers are made mostly of precisely cut metal components and direct light through a series of lenses, mirrors and diffraction slits shaped like a W. While this setup provides a high degree of accuracy, slight mechanical shifts caused by bumps or even temperature changes can create misalignments.

Wax's design, however, takes the light on a circular path within a housing made mostly from 3D-printed plastic. Because the spectrometer light path is circular, any expansions or contractions due to temperature changes occur symmetrically, balancing themselves out to keep the optical elements aligned. The device also uses a larger detector at the end of the light's journey to make misalignments less likely.

Traditional OCT machines weigh over 60 pounds, take up desk space and can cost between $50,000 and $120,000. The new OCT device weighs four pounds, has a much smaller footprint and, Wax expects, will be sold for under $15,000.

"Right now OCT devices sit in their own room and require a PhD scientist to tweak them to get everything working just right," said Wax. "Ours can just sit on a shelf in the office and be taken down, used and put back without problems. We've scanned people in a Starbucks with it."

In the new study, J. Niklas Ulrich, retina surgeon and associate professor of ophthalmology at the University of North Carolina School of Medicine, put the new OCT scanner to the test against a commercial instrument. He performed clinical imaging on both eyes of 60 patients, half from healthy volunteers and half with some sort of retinal disease.

To compare the images produced by both machines, the researchers used contrast-to-noise ratio -- a measure often used to determine image quality in medical imaging. The results showed that, by this metric, the low-cost, portable OCT scanner provided useful contrast that was only 5.6 percent less than that of the commercial machine, which is still good enough to allow for clinical diagnostics.

Wax is commercialising the device through a start-up company called Lumedica, which is producing and selling first-generation instruments for research applications.