Researchers eye retinal mapping.

Researchers eye retinal remapping

Technology being developed by NASA for spacecraft orientation and docking operations may one day help patients suffering from vision defects. Richard D. Juday of the NASA Johnson Space Center in Houston and David S. Loshin of the University of Houston College of Optometry are experimenting with a prototype "programmable remapper" that shows promise for patients with a variety of vision-reducing conditions known as field defects.

The defects -- caused by syndromes such as age-related maculopathy and retinitis pigmentosa -- affect the eye's retina and leave patients with part of their visual field missing or distorted. Patients with a central field defect, for example, have a relatively large "blind spot" in the middle of the visual field, making reading and facial recognition difficult. For others, the periphery of the image may be missing, or the image may be fragmented.

The programmable remapper, says Loshin, is a "field compensation" device that can take information from a given coordinate system and remap it onto another coordinate system. In the case of a retinal defect, it remaps or relocates information that otherwise would be missed. "It's taking information falling within a scatoma, or blind area, and taking it out and putting it onto viable [parts of the] retina."

It does so essentially by "stretching" hidden information -- such as typewritten words in the middle of the visual field -- around the defective area. Although the redistribution of this information results in a distorted image, preliminary results show the increase in information provides a net benefit to at least some patients.

The prototype model is too large and expensive for everyday use; the computerized components alone fill a unit the size of a small refrigerator. However, Loshin says, chip designers have assured NASA that the complex algorithms and "look-up" boards the system uses to remap defective coordinate systems all could fit onto a single silicon chip. In that case, the entire unit -- which would include a tiny, closed-circuit TV camera, a mechanism for tracking eye movements (to see where the eyes are looking) and a tiny projector that would display the remapped images for the eyes--could be mounted on a pair of glasses. NASA will conduct clinical trials of the prototype system this fall.

"We've shown static, remapped pictures to patients ... and they claim they can read more easily," Loshin says, "although whether it's going to increase their reading rate we don't know yet." As demonstrated in a sample videotape, shown last week at the World Congress on Medical Physics and Biomedical Engineering in San Antonio, Tex., the technique's benefits are more obvious when seen in moving-picture format. As the camera scans a page, it remaps instantly -- with the warped but mostly readable remapped information flowing smoothly around the defect.

Remapping faces is more difficult than remapping pictures or words, Loshin says. In preliminary work, "we were taking the [blocked-out] nose and remapping the nose all the way around the central field defect, and that doesn't really help to recognize the face." Although subsequent programs are proving more useful, he says, "I think there's going to have to be another kind of algorithm for faces, to try to get some more information from the eyes and maybe the mouth."

For patients with peripheral defects, mobility is a problem because it's difficult to perceive approaching objects or close-at-hand landscapes. By taking peripheral imagery that otherwise would be lost and remapping it toward the center of the retina, Loshin predicts, the system should enable patients to avoid approaching objects -- although distortion may preclude them from knowing precisely what is coming. "I may not know what it is [that's coming]," Loshin says, "but I don't care if it's a Buick or a Volkswagen. I don't want it to hit me."

The technology was originally developed by the military for missile guidance and adapted by NASA to create pattern-recognition systems that would help astronauts orient their crafts for docking operations and to aid in retrieving satellites.