EXTENDED WEARING TRIAL OF TRIFIELD PRISM VISUAL AID FOR "TUNNEL VISION" AMONG PATIENTS WITH RETINITIS PIGMENTOSA OR CHOROIDEREMIA

Abstract

Abstract: : Purpose: "Tunnel vision" (severely restricted visual fields) impairs mobility. We evaluated a novel spectacle–based prism device proposed to assist such patients (Woods & Peli, ARVO 2002) in a 7–visit wearing trial using several functional performance measures. Methods: To extend the visual fields, two prisms separated by a vertical junction (like a Franklin bifocal) were fitted apex to apex over one eye. The other eye had a conventional correction. This creates visual confusion (two different objects with the same apparent direction). Nine patients with advanced retinitis pigmentosa or choroideremia and an average visual field width of 12±5degrees, wore the Trifield glasses for an average of 11±6 weeks. Adaptation to the change in perceived direction of objects seen through the prisms, a perceptual integration of the Trifield device, was evaluated with a pointing task. At study start and end we evaluated the ability to navigate and walk safely in an unfamiliar shopping mall and perceived quality of life using questionnaires (Rasch analysis). Results: Visual field expansion with Trifield glasses was demonstrated using perimetry. Patients reported detection of obstacles that would otherwise be outside their visual field. However, generally they were unable to determine the location of the obstacle and we found no adaptation to perceived direction. With Trifield glasses patients walked more slowly in the mall at the end of the study. There were no changes in mobility–related quality of life. At the end of the study, only 3 of 6 patients reported a benefit from Trifield glasses. It is possible that our study length did not provide sufficient time to adjust to the complex visual scene created by the Trifield glasses, particularly since patients only wore them about 0.5 hour per day. However, 10±2 months after completing the study only 1 of 5 patients continued to use Trifield glasses. Conclusions: Trifield glasses provided some benefit to some patients, by giving warning of nearby objects and aid in search for missing objects. However, the benefits were limited and only experienced by 3 out of 6 patients. Adaptation to binocular confusion is difficult even when it provides visual field expansion.

Keywords: low vision • clinical (human) or epidemiologic studies: systems/equipment/techniques • retinitis