Last Updated: 2008-05-26 9:00:41 -0400 (Reuters Health)

NEW YORK (Reuters Health) – Peripheral prism spectacles expand the visual field of patients with hemifield visual defects and significantly improve visual function and mobility, according to a study published in the May issue of the Archives of Ophthalmology.

Homonymous hemianopia — loss of visual capacity in one half of the visual field – results from damage to the primary visual cortex caused by stroke, trauma, or tumors. Previous lens adaptations to treat this condition shifted images to a functional part of the visual field or modestly expanded visual field, which caused central diplopia, Dr. Alex R. Bowers and his colleagues explain.

The device tested in the current study uses high-power prism segments placed across the width of the spectacle lens above and below the pupil area on the side of the field loss.

"The peripheral prism design offers the advantage of visual field expansion that is present all of the time and in all lateral positions of gaze," the authors point out. "Patients are taught to view through the central, prism-free area of the spectacle lens (never looking into the prisms), so that central diplopia does not occur."

To determine the functional utility of peripheral prism glasses, Dr. Bowers, at Schepens Eye Research Institute in Boston, and his group evaluated 43 patients with complete homonymous hemianopia fitted by 15 community-based vision rehabilitation practitioners.

Thirty-two subjects (74%) continued to wear the modified spectacles at week 6, and 20 (47%) were still wearing them 12 months later. Interviews with patients who discontinued indicated that further training may have helped them better adapt to the lenses.

Obstacle avoidance was a primary advantage to the lenses. According to the authors, "Long-term wearers reported that the prisms were particularly helpful when in shopping malls and stores and moving in crowded and unfamiliar areas."

Sixteen of 19 long-term wearers were willing to pay $600 for permanent prism glasses, "an indication of the perceived importance of the benefits of the glasses in their everyday lives."

Based on these promising results, Dr. Bowers’ team is now conducting a randomized, cross-over trial using real and sham prisms.

Arch Ophthalmol 2008;126:657-664.

Copyright Reuters 2008. Click for Restrictions