A Novel Acuity Testing Method

The primary objective of the project is to develop a valid, reliable, better standardized and more efficient test of visual acuity for use in clinical trials. Accuracy, precision, stability, and utility of the test will be assessed for non-inferiority with Early Treatment for Diabetic Retinopathy Study (ETDRS) protocol, the gold standard for acuity testing in clinical trials.

The experimental protocol (EVA-MOBS {Electronic Visual Acuity - Modified Binary Search}) utilizes a testing strategy that would appear to increase the efficiency and standardization of acuity threshold determination. A more efficient test is justified on the basis of reducing subject burden. Increased measurement efficiency may also reduce both subject- and tester-based bias, while allowing a better means to assess measurement stability through the collection of repeated measures data.

As part of the standard eye examination, replicated visual acuity assessments will be made during regularly-scheduled Clinic visits. Up to 500 opportunistically-sampled subjects from the National Eye Institute will be tested both with the ETDRS and EVA-MOBS protocols over a 12 month study period. Similar testing will take place at two other institutions (Devers Eye Institute, Portland, OR; The Retina Foundation of the Southwest, Dallas, TX) and the data from all three institutions will be combined and analyzed at the JAEB Center (Tampa, FL). Subjects will range in age from 7 years to 90 years and will be classified by clinical diagnosis (normal, high refractive error, age-related macular degeneration, cataract, optic nerve abnormality, corneal abnormality, uveitis, glaucoma, retinal/choroid abnormality, amblyopia and other criteria). First, those with poor acuity will be oversampled by increasing the chance that they will be selected for this testing. Second, patients will only be selected for this extra testing if it will not seriously delay clinic operations on any given day. Order of acuity test type will be randomized. It is estimated that up to 10 patients per day can have this testing performed without compromising clinic operations.

The experimental protocol runs on a Palm handheld that is used to provide instructions to the tester, record the subject's responses, and communicate with a PC/monitor at a test distance of 3 meters. Stimuli are high contrast black-and-white ETDRS letters presented on an ultra high resolution FD Trinitron monitor, that subtend 2.5 to 200 min of arc; each letter appears in isolation under equiluminant conditions, and is flanked with black bars to simulate visual crowding.

Acuity scores will be compared, with the ETDRS score serving as the reference standard. Stability of the acuity estimates from the EVA-MOBS protocol will be assessed with data from repeated measures. A short questionnaire will be administered, following the last acuity test, to determine whether a test type preference exists.

If results indicate that the protocol is well tolerated by clinical populations and that thresholds are accurate, precise, and stable, the method will be standardized for use in future trials. Use of stimuli to test visual resolution acuity, such as the Landolt-C, may subsequently be evaluated.