Evaluation of the Night Vision Spectacles on patients with impaired night vision

Background: The Night Vision Spectacles (NiViS) were developed by a consort ium of European companies to assist individuals who suffer from impaired ni ght vision. They consist of a head-mounted video camera (input) and binocul ar displays (output) connected to a portable computer processor, which uses an algorithm to enhance the luminance and contrast of the video image. Met hods: Eighteen patients with impaired night vision were tested, including t hose with retinitis pigmentosa (7), Usher syndrome (2), fundus albipunctatu s (1) and complete (4) and incomplete (4) congenital stationary night blind ness. Normal trichromats (3) and typical, complete achromats (2) acted as c ontrols. A battery of tests assessed: visual acuity at 5 m (projection unit ) and 1 m (chart) and at high and low contrasts; contrast sensitivity; abso lute and increment threshold; the influence of glare; contrast motion detec tion; and hand-eye performance. The tests were performed, with and without the NiViS, at three adaptation levels: low scotopic (10(-3) cd/m(2)), high scotopic (10(-2) cd/m(2)) and mesopic (10(-1) cd/m(2)). Results: At the low and high scotopic levels, the majority of patients showed improved perform ance on the visual acuity, contrast sensitivity and motion contrast tests w ith the NiViS. At the mesopic level, the advantage with the NiViS was great ly reduced, but still present for contrast sensitivity. Conclusion: Patient s with impaired night vision can benefit from the NiViS when performing tas ks involving contrast and motion perception. Those with normal visual field s and retaining good photopic vision will benefit more than those with cons tricted visual fields and impaired cone vision. Recommendations regarding d esirable improvements of the NiViS and suitability for the individual patie nt are given.