How the Eye Goes Awry

Mention strabismus, and the not-uncommon crossed or lazy eyes of childhood come to mind. But both children and adults may struggle with another eye imbalance that's more difficult to treat, a vertical strabismus in which one eye points higher than the other.

Vertical strabismus typically stems from paralysis of the fourth cranial nerve overseeing the orbital muscles. "People compensate for it, if the difference in gaze is small," says neurologist David Zee, M.D., but great disparity-the sort that brings double vision and flawed depth perception-needs outside help. Surgery is the usual answer: Ophthalmic surgeons operate on the muscles and reattach their tendons at a different spot on the eyeball.

The quiet reality, however, is that surgical results can be less than sublime. "In the best of hands," says Zee, "over- or under-correction is still high" and a second go in the OR isn't unusual.

The problem isn't suspect surgery. Rather, it's having too little information about the particular orbital muscles affected and how they go awry. And broadly, no one understands how the brain, in trying to compensate for the problem, governs those muscles. Zee, however, aims to change that, first by clarifying what goes on eye-wise and then by learning the brain's role throughout.

As a first step, his team, which includes Hopkins ophthalmologists, uses high-resolution MRI to image eye muscles while patients gaze in set directions. Changes in muscle girth show which muscles work at each position. The team found that patients with acquired vertical strabismus-they fall off bikes or get head blows-are more likely to show abnormalities in different muscles from those in people with congenital forms.

Most important, the team has found that patterns of eye motion in patients trying to compensate for double vision may give important clues to what kind of surgery they need.