The three point vernier alignment or acuity test (3Pt VA test): an analysis of variance

A very useful clinical vernier acuity or vernier alignment test has been de veloped in this and associated laboratories over a span of two decades. We seek to refine further this test, to seek internal inconsistencies and to o ptimize parameters used in a variety of devices and environments. Vernier t esting, and many aspects of this work have been considered by numerous able scientists over a long time period (not reviewed here), but none have enco untered conditions faced by this group, particularly in the developing worl d. The three point vernier alignment (acuity) threshold test (3Pt VeA test) em ployed here has broad applications; it can be used as a clinical test of vi sion status, for triage, and as a reference standard for vision testing (in general). As one example, if sufficient luminance is employed, the test is applicable in the presence of truly dense media disorders, even advanced l eucomas, mature cataracts, intraocular bleeds, as well as combinations of t hese disorders, with or without a window to the retina. Only retinal and ce ntrally-based neural disorders, eccentricity from fixation, and about 50% o f hypermature cataracts affect outcomes. With minor alterations, this test can be employed to assess the visual field. An analysis of variance (ANOVA) was performed on a defined set of parameters, to enable us to understand b etter the special properties and requirements associated with this test. Re sults are not significantly altered between ages 10-94 years (not assessed here). Employing settings well above threshold for test spot detection and well separated individual test spots, changes in test spot luminance, or ba ckground luminance (or adaptation level), contrast, veiling glare, test spo t size, clear and variously degraded images, seem not to affect meaningfull y measured outcomes. If an observer can define well a center of gravity for each test spot viewed, he can align the three points with remarkable preci sion. (C) 2000 The College of Optometrists. Published by Elsevier Science L td.