In a study of specially designed peripheral prism glasses for hemianopia patients (blinded in half the visual field in both eyes), scientists found that two-thirds of patients continued to wear the glasses at the end of the study period and beyond, indicating a high level of success.
They also found that the brains of patients had not fully remapped to adjust for the prisms, which means that improved training in their use could further enhance the benefits, says principal investigator, Dr. Eli Peli, a senior scientist at Schepens Eye Research Institute and inventor of the glasses.
The study, published in the May 2009 issue of Optometry and Vision Science, not only reaffirms previous clinical studies, but also adds a deeper understanding of the neurological processes at play when a patient uses prisms for this purpose, adds Peli.
More than a million Americans suffer from hemianopia, which blinds the vision in one half of the visual field in both eyes -- the result of strokes, tumors or trauma. Hemianopia patients are often unaware of what they cannot see and frequently bump into walls, trip over objects or walk into people on the side where the visual field is missing.
The prisms, attached above and below the center of a spectacle lens in Peli's invention, shift images from one side of the visual field to the other side and alert patients to objects and obstacles not otherwise visible to them. Alerted to the existence of these objects, patients turn to look, or, if their brains are fully adapted (remapped), perceive quickly where the objects are and automatically avoid them without turning their eyes and head. (In earlier designs by other scientists, the prism was in the middle of the lens and caused double vision.)
"The best case scenario," says Peli, "is for a patient to be able to make rapid decisions based on the perception rather than moving their heads when an unseen object is detected."
Peli and his team asked 28 patients with complete hemianopia to wear the peripheral prism glasses as much as possible for the duration of the study, which averaged about nine weeks. Success was measured by continued wear, visual field expansion, perceived direction (caused by brain remapping), and perceived improvement in quality of life.
The research team found that 67 percent of patients chose to continue to wear the glasses at the end of the study. They also found that all patients had expansion of their visual field of about 22 degrees and expressed reduced difficulty in noticing and avoiding obstacles. On the other hand, only two patients demonstrated even an intermittent adaptation to the change in visual direction produced by the peripheral prism glasses, which means that no patient had remapped his or her brain to automatically make the perceptual adjustment.
Based on these results, Dr. Peli and his team plan to conduct future research that will examine the best way to train patients to reprogram their brains to perceive direction automatically.
The research team consisted of Mr. Robert Giorgi and Drs. Russell Woods and Eli Peli, all of the Schepens Eye Research Institute.
This study was conducted with a prototype of the glasses, on which the prisms are temporarily applied. There are now permanent prism glasses available, which continue to be studied and perfected in on-going multi-center trials.
Patients interested in trying the peripheral prism glasses can contact Chadwick Optical for referral to a doctor in their area. Go to http://www.chadwickoptical.com/ for contact information.
Schepens Eye Research Institute is an affiliate of Harvard Medical School and the largest independent eye research institute in the nation.