The Machine With a Vision

The watchmaker, draftsman and student who spend hours squinting over their work may soon have less trouble focusing if Harvard researchers can apply recent findings on near-sightedness, uncovered through the youthful science of biomechanics.

Thomas McMahon, McKay Professor of Applied Engineering and author of McKay's Bees, and his research assistant Peter Greene specialize in biomechanics, a newly invented scientific method which unites biology and engineering. Constructing synthetic models of limbs, eyes and other body parts, the pair attempt to solve medical problems by discovering, simply, what went wrong in the mechanics. They have already made headlines for their peculiar specialty: in 1977, they experimented with artificial legs to discover the ideal running ground and came up with the celebrated new track for Harvard's Indoor Tennis and Track Building. The track has both improved the team's times and decreased its injuries. In their lifesized dummy of the human leg, aluminum bars substitute for bones, simple springs for muscles and a fluid shock absorber for tendons. When the same surface they designed from their model was put down in Madison Square Garden, records fell and McMahon and Greene found themselves sought after by the unlikely technical journals, Sports Illustrated and The New Yorker, for cover stories.

Their latest toy is an artificial eye. Though McMahon and Greene are just starting to apply biomechanics to myopia, its potentials alone signify a major advance. The field has long been what Greene calls a "thicket of controversy." No study has conclusively settled the origins of myopia, nor how much heredity or eye-strain is to blame. "Myopia has been associated with everthing from pregnancy to tooth decay," Greene says. Researchers agree only that myopia is the abnormal bulging of the back of the eye or "posterior sclera," usually around the gap for the optic nerve. But no one is sure what causes the swelling, whether myopics are born with bulge or have brought it on themselves by reading in dark corners.

Recent experiments with animals led McMahon and Greene to apply their methods to eyes. Dr. Torsten N. Wiesel, professor of Neurobiology, and Dr. Elio Raviola, professor of Anatomy at the Medical School, did experiments in which they forced monkeys to read, and found that they quickly developed myopia. Dr. J. Wallman at New York University discovered that chickens, when forced with blinders to look straight ahead instead of sideways as they normally do, also become near-sighted. These results indicate that myopia can be induced. Further, because the animals' eyes degenerated at similar rates, which can be computed mathematically, McMahon and Greene deduced that the answer might lie in mechanics.

So McMahon and Greene set to work building a mechanical eye. The model immediately provided two insights. First, strain occurs when the two oblique muscles--the muscles in the back of the eye which control its rotation--are tensed greatly, as in reading. The tension stretches and strains the sclera. Though such stretching is normally elastic, if it is both frequent and extreme enough the sclera does not return to its normal position and myopia develops. Second, the eye is least able to reduce strain near the point where the optic nerve enters the eye--Greene draws an analogy with the rivet holes in airplane wings, the weakest point of an airplane's body. This factor may explain why myopia is concentrated about the optic nerve.

The biomechanical model shows that myopia is both acquired and inherited. Excessive stress may explain how it is acquired, while location of the oblique muscles explains how it may be inherited. If someone is born with their oblique muscles attached near the optic nerve, they are more prone to myopia than most individuals.

McMahon and Greene have come up with several possible solutions, but have tested none so far. One is the surgical relocation of the oblique muslcles, which Greene claims is a relatively simple operation. Another is to flare surgically the point of attachment of these muscles, dispersing the strain. McMahon and Greene also talk about prescribing prismatic eyeglasses, lenses which dupe the eyes into "thinking" they are focused on a distant point. These solutions remain speculative, but for the 30 to 40 per cent of all Americans who suffer from myopia, hope is in sight.

'Myopia has been associated with everything from pregnancy to tooth decay.'