The modern microscope has given science an unmatched window on the world of the very small.
Now, a new type of technology is offering ophthalmologists a similar perspective on the eye, providing detailed cross-sectional images of the retina--the delicate tissue that harbors the eye's light-sensing machinery.
The technology is optical coherence tomography (OCT), and it's the latest product of an ongoing collaboration between Professor James Fujimoto of the Department of Electrical Engineering and Computer Science (EECS) and the Research Laboratory of Electronics; Carmen Puliafito, head of the New England Eye Center in Boston; and Eric A. Swanson, an assistant group leader at Lincoln Laboratory.
Michael Hee, an MD/PhD student in EECS and one of the developers of OCT, noted that the system resembles in principle another medical technology. "It's similar to ultrasound," he said, "but it uses light instead of sound."
The system works by comparing a reference light beam to one that goes into the retinal tissue. Measuring the tiny differences in how long it takes the two beams to be reflected, the device allows for stunningly detailed images of the retina.
Consider how OCT is used to diagnose macular holes--tiny openings that can develop in the macula, a retinal structure located opposite the eye's lens. The problem, relatively common in older women, doesn't cause blindness but it can cost patients the kind of vision used in tasks like reading. OCT reveals such holes down to a diameter of one-tenth of a millimeter, or about the twice the width of a human hair.
Traditional systems which only image surfaces can't come close to the acuity provided by OCT's cross-sectional capabilities. Such instruments, said Mr. Hee, "may offer hints of some sort of irregularity, but you can't be sure it's a macular hole."
Mr. Hee said OCT is likely to become the approach of choice for diagnosing macular holes. But the system may also be used to catch early hints of diabetic retinopathy-the vision-threatening swelling of the retina that afflicts many diabetics. In addition, it could offer clues to glaucoma's presence long before the disease has a noticeable impact on vision.
Glaucoma, the third-leading cause of blindness in the United States, injures the nerves carrying signals from the eye to the brain. However, in the disease's early stages, it's difficult to diagnose. "You can lose 50 percent of your nerve tissue before signs of the problem show up in a visual field exam," said Mr. Hee.
OCT may help identify the ailment long before then by revealing a subtle thinning of the nerve layer. "We've already shown we can differentiate individuals with healthy eyes from patients known to have glaucoma," said Mr. Hee. "Now, we're planning a multi-center patient trial to see if we can identify the disease in individuals who are at risk for the disease but haven't been diagnosed with it."
Professor Fujimoto is one of several faculty members associated with the Research Laboratory of Electronics who will be presenting talks on current research at the RLE's 50th anniversary celebration November 1-2. His talk will be part of a symposium from 10am-1pm on November 2 in the Tang Center (Building E51). For more information on the celebration, call Dorothy Fleischer at x3-4653.
A version of this article appeared in MIT Tech Talk on September 25, 1996.