|
Using high luminance point-of-light stimuli, Vernier judgments can be made in the presence of markedly degraded retinal imagery. Without coaching, observers perform center-of-gravity assessments of relative locations of degraded point images. We seek to define, presurgery, individuals who will derive the most benefit from advanced cataract removal (a form of triage), and to determine which of two cataractous eyes has the better postsurgical visual prognosis. There are incredible and growing backlogs of patients with severe cataracts (and other dense media opacities) in the developing world, and generally, limited resources are available for provision of health care. Postcataract surgical failure rates for good visual function are often high, and only one eye is operated on in over 95% of indigent patients treated. Prior to initiating advanced studies in the developing world, at Berkeley we conducted preliminary research on Vernier acuity test techniques on normal adult subjects. We sought to determine the number of repeat trials necessary; to compare a two-point and a three-point Vernier display; to determine the shape of the measured response function at large gap separations between test points (required when testing advanced cataract patients); to assess the effect(s) of a broad range of uncorrected refractive errors on outcomes; and to consider means to minimize refraction-based errors. From these and prior data and analyses, we defined a protocol for use in the developing world. Using a newly designed and rugged precision instrument, these tests were repeated on an advanced cataract population at Aravind Eye Hospital in Madural, India. Although we had much prior experience in India, the initial protocol required major revision on site. Necessary changes in test methods and analytical approaches were made, and next stages in this program were planned. And a new and simple gap "visual acuity" (gap "VA") test was added to the protocol, which greatly facilitated the outcome. The presented material is of interest for several reasons: The health care problems addressed are of considerable social and economic importance; it is valuable to compare the initial protocol and instrument defined in Berkeley and the resultant protocol and instrument designs that finally evolved in India; and the difficulties encountered when seeking to adapt what we thought were simple techniques to patient populations and technical personnel in a "small town setting" (ca. 1 million inhabitants in Madurai alone) in rural south India, are worthy of note. We point out that the Aravind Eye Hospital is an ophthalmological exemplar in the developing world.
|
