Optical Coherence Tomography (OCT): A new optical device to scan eye disease

A new optical device puts the ability to find eye disease within the palm of a hand. The tool, about the size of a handheld video camera scans a patient's entire retina in seconds. If found something, doctors will aid the patients within the early detection of retinal diseases as well as diabetic retinopathy, glaucoma and macular degeneration. Researchers at the Massachusetts Institute of Technology (MIT) describe their new ophthalmic-screening instrument during a paper published today within the open-access journal Biomedical Optics express, published by The Optical Society (OSA).

Power grip style (A-B) and
camcorder style design (C-D)
of the prototype OCT scanner
(Credit: Biomedical Optics Express)

Although alternative research groups and companies have created handheld devices using similar technology, the new design is the first to mix innovative technologies like ultrahigh-speed 3D imaging, a little micro-electro-mechanical systems (MEMS) mirror for scanning, and a method to correct for unintentional movement by the patient. These innovations, the authors say, ought to allow clinicians to gather comprehensive data with only one measurement.

Normally, to diagnose retinal diseases, an ophthalmologist or optometrist should examine the patient in his or her workplace, with tabletop instruments. However, few people visit these specialists often. To improve public access to eye care, the MIT group, with the University of Erlangen and Praevium/Thorlabs, has developed a transportable instrument that may be taken outside a specialist's workplace.

"Handheld instruments will enable screening a wider population outside the normal points of care," said researcher James Fujimoto of MIT, an author on the biomedical Optics Express paper. For example, they will be used at a primary-care doctor's workplace, a pediatrician's office or perhaps in the developing world.

How it Works

The instrument uses a technique known as Optical Coherence Tomography (OCT), 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 that uses interferometer to measures changes in the time delay and extent of the returning light echoes, revealing the cross-sectional tissue of the membrane -- like radar or ultrasound imaging. Tabletop OCT imagers became a typical of care in ophthalmology, and current generation handheld scanners are used for imaging infants and overseeing retinal surgery.

The researchers could shrink what has been an oversized instrument into a transportable size by employing an MEMS mirror to scan the oct imaging beam. They tested two designs, one among that is comparable to a handheld video camera with a flat-screen display. In their tests, the researchers found that their device would get images comparable in quality to standard tabletop OCT instruments used by ophthalmologists.

To deal with the motion instability of a handheld device, the instrument takes multiple 3D images at high speeds, scanning a specific volume of the eye many times however with different scanning directions. By using multiple 3D images of the same a part of the retina, it is possible to correct for distortions owing 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. However, the device remains expensive, he added, and before this technology finds its means into doctors' offices or within the field, manufacturers will have to be compelled to find the simplest way to support or lower its price.

Why Early Screening is important

Many people with eye diseases might not even be aware of them until irreversible vision loss happens, Fujimoto said. Screening technology is important because several eye diseases ought to be detected and treated long before any visual symptoms arise. For instance, during a 2003 Canadian study of nearly 25,000 people, nearly 15 percent were found to have eye disease -- even if they showed, no visual symptoms and 66.8 percent of them had a best-corrected eyesight of 20/25 or better. Issues with undetected eye disease are worsened with the increase of obesity and undiagnosed diabetes, Fujimoto said. The center for disease control and prevention estimates that 11.3 percent of the U.S. population over the age of 20 has diabetes, even if many do not understand it.

In the future, Fujimoto envisions that handheld OCT technology will be used in several other medical specialties beyond ophthalmology -- for instance, in applications ranging from surgical guidance to military medicine.

"The handheld platform allows the diagnosis or screening to be performed in a much wider range of settings," Fujimoto said. "Developing screening methods that are accessible to the larger population may reduce unnecessary vision loss."