Handheld OCT Device Catches Eye Disease Early
CAMBRIDGE, Mass., Dec. 23, 2013 — A handheld optical device that combines ultrahigh-speed 3-D imaging with a microelectromechanical systems (MEMS) scanning mirror could make early detection of certain eye diseases as easy as scanning a bar code.
Photographs of the power grip style (A-B) and camcorder style designs (C-D) of the prototype OCT scanner developed at MIT. Both devices acquire 3-D OCT images of the retina. Images courtesy of Biomedical Optics Express.
The ophthalmic-screening instrument uses optical coherence tomography (OCT) to scan a patient's retina in seconds and could aid primary-care physicians in the early detection of a host of retinal diseases, including diabetic retinopathy, glaucoma and macular degeneration. It was developed at MIT and is about the size of a handheld video camera.
Although other groups and some companies have created handheld devices using similar technology, MIT's is the first to use cutting-edge techniques such as 3-D imaging, MEMS, and a technique to correct for a patient's unintentional movements. These innovations, the team says, should allow clinicians to collect comprehensive data with just one measurement.
Normally, to diagnose retinal diseases, an ophthalmologist or optometrist must examine the patient in his or her office, typically with tabletop instruments. However, few people visit these specialists regularly, and many people are not aware they have eye diseases until irreversible vision loss occurs. Screening is important because many eye diseases should be detected and treated long before any visual symptoms arise.
To improve public access to eye care, the MIT group, in collaboration with the University of Erlangen and Praevium/Thorlabs, developed a portable instrument.
"Handheld instruments can enable screening a wider population outside the traditional points of care," said MIT researcher James Fujimoto of MIT, who, with collaborators, helped pioneer OCT at MIT in the early 1990s. For instance, the instruments can be used at a primary-care physician's office, a pediatrician's office or even in the developing world.
A high-definition OCT image of the retina allows clinicians to noninvasively visualize the 3-D structure of key regions, such as the macula (region near the fovea) and the optic nerve head, to screen for signs of disease pathology. Shown is a wide-field view (A) as well as detailed vertical cross sections (B), (C) and (D) and a circular cross section (E).
In OCT, beams of IR light are sent 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 — similar to radar or ultrasound imaging. 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 shrunk 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 similar to a handheld video camera with a flat-screen display. They found that their device could acquire images comparable in quality to conventional tabletop OCT instruments.
To deal with the motion instability of a handheld device, the instrument takes multiple 3-D images at high speeds, scanning a particular volume of the eye many times but with different scanning directions. By using multiple 3-D images of the same part of the retina, distortions resulting from motion of the operator's hand or the subject's own eye can be corrected.
The next step, Fujimoto said, is to evaluate the technology in a clinical setting. But the device is still relatively expensive, and before the technology finds its way into doctors' offices or in the field, manufacturers will have to find a way to support or lower its cost, he added.
The technology could be used in medical specialties beyond ophthalmology; e.g., in applications ranging from surgical guidance to military medicine, he said.
The research appears in Biomedical Optics Express http://dx.doi.org/10.1364/BOE.5.000293
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