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

Abstract

A very useful clinical vernier acuity or vernier alignment test has been developed in this and associated laboratories over a span of two decades. We seek to refine further this test, to seek internal inconsistencies and to optimize parameters used in a variety of devices and environments. Vernier testing, and many aspects of this work have been considered by numerous able scientists over a long time period (not reviewed here), but none have encountered conditions faced by this group, particularly in the developing world. The three point vernier alignment (acuity) threshold test (3Pt VeA test) employed here has broad applications; it can be used as a clinical test of vision 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 leucomas, mature cataracts, intraocular bleeds, as well as combinations of these disorders, with or without a window to the retina. Only retinal and centrally-based neural disorders, eccentricity from fixation, and about 50% of 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 better the special properties and requirements associated with this test. Results 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 background luminance (or adaptation level), contrast, veiling glare, test spot size, clear and variously degraded images, seem not to affect meaningfully 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 precision.

Forever Young: Visual Functions Not Affected or Minimally Affected by Aging: A Review

“…It is assumed, a priori, that each of the stimuli in the vernier display (e.g., points, lines) is distinguishable from the other one(s). Thus, this is not a resolution or a visual acuity task (20)(21)(22)(23)(24)(25)102,103), and, in addition, it is not a threshold detection task (66). Vernier thresholds in normal individuals (and hyper- .s;…”

“…After instruction, at each gap tested, 10 determinations were made. High and low readings in a data set were dropped, and the bias and precision for the remaining group of eight readings were determined (55,60,61,64,66,76,77). The twopoint vernier test display was presented first, and this was followed by the three-point vernier test display.…”

“…Studies ofVeA as a function of age were conducted under a variety of conditions (56,57,60,76,77). A recent study of normal observers has shown that not only age, but also varying luminance, contrast, test stimuli sizes, test stimuli degradations, test distances (all within specific parametric ranges) do not significantly alter outcomes ifthe individual points of light do not overlap, and these stimuli are presented at superthreshold levels (66). Not surprisingly, responses obtained using degraded images may have somewhat higher thresholds.…”

“…When testing vernier acuity in the presence of image degradation, if sufficient separations of display features (or gap separations) exist between the test objects viewed, the individual, without prompting, determines the centers of gravity (mean position or centrum) of the degraded test points, and aligns them with surprising precision if the retinal images are above threshold detection. This feature is important when assessing vision of patients with dense media opacities, even without a "window" through their opacities (60)(61)(62)(63)(64)66). By such means, potential postsurgical visual performance can be predicted.…”

Visuospatial interpolation in typically developing children and in people with Williams Syndrome

“…First, many experimental procedures for measuring visual interpolation are well suited for testing children and atypical populations because they are easy to understand. One common interpolation task is the three-point Vernier alignment task, which is used to efficiently assess retinal and cortical impairments in children (Kim, Enoch, Fang, Lakshminarayanan, Kono, Strada & Srinivasan, 2000), older adults (Yebra-Pimentel Vilar, Giraldez-Fernandez, Enoch, Lakshminarayanan, Knowles & Srinivasan, 1995) and clinical populations (Fang, Enoch, Lakshminarayanan, Kim, Kono, Strada & Srinivasan, 2000). In this task, observers are asked to judge the position of a central dot relative to flanking dots (see Fig.…”