Dynamic visual acuity: Normative functions and practical implications

Advances in dynamic visual acuity test research

The dynamic visual acuity test (DVAT) is a functional evaluation tool for the impairment and compensation of the vestibular system, which could reflect the Vestibulo-ocular reflex (VOR) function. We present an overview of DVAT research, displaying recent advances in test methods, application, and influencing factors; and discussing the clinical value of DVAT to provide a reference for clinical application. There are two primary types of DVAT: dynamic-object DVAT and static-object DVAT. For the latter, in addition to the traditional bedside DVAT, there are numerous other approaches, including Computerized DVAT (cDVAT), DVAT on a treadmill, DVAT on a rotary, head thrust DVA (htDVA) and functional head impulse testing (fHIT), gaze shift dynamic visual acuity with walking (gsDVA), translational dynamic visual acuity test (tDVAT), pediatric DVAT. The results of DAVT are affected by subject [occupation, static visual acuity (SVA), age, eyeglass lenses], testing methods, caffeine, and alcohol. DVAT has numerous clinical applications, such as screening for vestibular impairment, assessing vestibular rehabilitation, predicting fall risk, and evaluating ophthalmology-related disorders, vestibular disorders, and central system disorders.

A novel computer software for the evaluation of dynamic visual acuity

Purpose

Dynamic visual acuity (DVA) is defined as the ability to discriminate fine details in a moving target. Albeit a growing interest in DVA, there is a lack of standardized, validated instrumentation and procedures for the assessment of this visual function parameter. The aim of the present study was to analyze qualitative construct validity and test–retest reliability of a novel, computer-assisted instrument (DinVA 3.0) for the measurement of DVA.

Methods

Two different experiments are presented, involving the participation of 33 subjects. The first experiment aimed at testing qualitative construct validity of the DinVA 3.0 by comparing the outcome of a series of trials consisting in different speeds, contrasts and trajectories of the target stimuli with those reported in the literature. The second experiment assessed test–retest reliability by repeating a series of trials at three different time intervals, at maximum target stimuli contrast and either high or low speed configurations.

Results

The results of the first experiment gave support to the qualitative construct validity of DinVA 3.0, as the DVA scores were found to be modulated by the speed of the moving target (high speeds yielded lower DVA), contrast (high contrast resulted in better DVA) and trajectory (DVA was better at horizontal rather than oblique trajectories). Test–retest reliability was found to be good, with a small insignificant trend towards improvement with learning.

Conclusion

The DinVA 3.0 proved to be a valid and reliable instrument for the assessment of DVA and may be considered a promising tool for both clinicians and researchers.

Comparison of dynamic visual acuity between water polo players and sedentary students

In this study, we examined differences in dynamic visual acuity between elite and subelite water polo players and sedentary students. To measure dynamic visual acuity binocularly, we asked participants to indicate the orientation of a broken ring, similar to the Landolt C, which increased in size as it moved across a computer screen. Two different speeds, three possible trajectories, and two different levels of contrast were evaluated. There were statistically significant differences between elite players and sedentary students for each combination of speed, contrast, and trajectory. Elite players achieved better dynamic visual acuity scores, and results also improved for some combinations of speed, contrast, and trajectory. Comparison between elite and subelite groups failed to reveal any

A portable device for the assessment of dynamic visual acuity

Dynamic visual acuity (DVA) thresholds are among the few visual functions predictive of automobile crashes. DVA is also sensitive to alcohol and aging. However, measuring DVA is awkward because there is no standardized, efficient, flexible apparatus for DVA assessment. In this project, we developed a prototype of an automated, portable DVA system using a low-energy laser, and we compared this laser DVA with the traditional device in two within-subjects, repeated measures designs. The two studies included 48 participants (22 males and 26 females with an average age of 18.33 years). The most important findings were that: (1) retest reliabilities of the two DVA devices were comparable and higher with the laser; (2) average correlations between the two devices were r=0.62 (p<0.01) and r=0.65 (p<0.01) for the two designs respectively; and (3) after correction for reliability attenuation these improved to r=0.92 and r=0.78. These findings indicate that a flexible DVA laser device can be developed to measure the same construct as the more traditional bulky DVA device.

The shape and size of crowding for moving targets

Our ability to identify alphanumeric characters can be impaired by the presence of nearby features, especially when the target is presented in the peripheral visual field, a phenomenon is known as crowding. We measured the effects of motion on acuity and on the spatial extent of crowding. In line with many previous studies, acuity decreased and crowding increased with eccentricity. Acuity also decreased for moving targets, but the absolute size of crowding zones remained relatively invariant of speed at each eccentricity. The two-dimensional shape of crowding zones was measured with a single flanking element on each side of the target. Crowding zones were elongated radially about central vision, relative to tangential zones, and were also asymmetrical: a more peripheral flanking element crowded more effectively than a more foveal one; and a flanking element that moved ahead of the target crowded more effectively than one that trailed behind it. These results reveal asymmetrical space-time dependent regions of visual integration that are radially organised about central vision.

Implications for dynamic visual acuity with changes in aged and sex

Using a Landolt ring with a gap of 40' of arc which moved at a decreasing velocity until the gap was discriminated, we measured the dynamic visual acuity of 826 subjects, males and females ages 5 to 92 years, and found rapid development between the ages of 5 and 15 years. This experiment showed that dynamic discrimination peaked at age 15 and then declined at a constant rate from age 20 on. The discrimination of male subjects was superior to that of female subjects at most ages, but a significant sex difference was observed only at age 5. We speculate that males may have better discrimination than females but variability is substantial.

Training effects on dynamic visual acuity with free-head viewing

Training effects on dynamic visual acuity (DVA) were determined over a range of target durations and target velocities under the viewing condition of free-head movement. Dynamic acuity levels were lower than static acuity levels, and training was found to be very effective in improving performance, particularly under the most difficult conditions in which performance was poorest. Improvement was also most evident among those observers who initially exhibited the poorest DVA scores. Preliminary comparisons between DVA scores of a nonselect sample of college students and those of a small group of college athletes indicated that the athletes were not very different from the nonselect group and would also benefit from training on the task.

The effects of target borders on dynamic visual acuity: practical and theoretical implications

The effects of target borders on the ability of observers to resolve moving targets (Landolt Cs) under a range of conditions were examined. Contrary to reported findings with stationary targets, it was predicted that the presence of borders would improve acuity for slow-moving targets because (i) overall stimulus energy is kept relatively constant as target detail varies, and (ii) a low-spatial-frequency component is held constant as target detail varies. In an experiment in which a two-sided border (above and below the target) was used, the predicted beneficial effect of the border at slow speeds was obtained. The results are discussed in terms of practical implications for the assessment of dynamic visual acuity as well as the potential neural mechanisms underlying performance.