A new optical device that could aid primary care physicians in the early detection of a host of retinal diseases has been developed by researchers at the Massachusetts Institute of Technology (MIT). The device is about the size of a handheld video camera and scans a patient’s entire retina in seconds.
The MIT researchers describe their new ophthalmic-screening instrument in a paper published in the open-access journal Biomedical Optics Express, published by The Optical Society (OSA).
The new design is the first to combine cutting-edge technologies such as ultrahigh-speed 3D imaging, a tiny micro-electro-mechanical systems (MEMS) mirror for scanning, and a technique to correct for unintentional movement by the patient. These innovations, the authors say, should allow clinicians to collect comprehensive data with just one measurement.
Normally, to diagnose retinal diseases such as diabetic retinopathy, glaucoma and macular degeneration, an ophthalmologist or optometrist must examine the patient in his or her office, typically with tabletop instruments. However, few people visit these specialists regularly. To improve public access to eye care, the MIT group, in collaboration with the University of Erlangen and Praevium/Thorlabs, has developed a portable instrument that can be taken outside a specialist’s office.
‘Handheld instruments can enable screening a wider population outside the traditional points of care,’ said researcher James Fujimoto of MIT, an author on the Biomedical Optics Express paper. For instance, they can be used at a primary-care physician's office, a pediatrician's office or even in the developing world.
The instrument uses a technique called optical coherence tomography (OCT), which the MIT group and collaborators helped pioneer in the early 1990s. The technology sends beams of infrared light into the eye and onto the retina. Echoes of this light return to the instrument, which uses interferometry to measures changes in the time delay and magnitude of the returning light echoes, revealing the cross sectional tissue structure of the retina. Tabletop OCT imagers have become a standard of care in ophthalmology, and current generation handheld scanners are used for imaging infants and monitoring retinal surgery.
The researchers were able to shrink what has been typically a large instrument into a portable size by using a MEMS mirror to scan the OCT imaging beam. They tested two designs, one of which is similar to a handheld video camera with a flat-screen display. In their tests, the researchers found that their device can acquire images comparable in quality to conventional tabletop OCT instruments used by ophthalmologists.
To deal with the motion instability of a hand-held device, the instrument takes multiple 3D images at high speeds, scanning a particular volume of the eye many times but with different scanning directions. By using multiple 3D images of the same part of the retina, it is possible to correct for distortions due to motion of the operator’s hand or the subject’s own eye. The next step, Fujimoto said, is to evaluate the technology in a clinical setting. But the device is still relatively expensive, he added, and before this technology finds its way into doctors' offices or in the field, manufacturers will have to find a way to support or lower its cost.