The Validation of a Novel Dynamic Visual Acuity Test, and Examination of the Effects of Different Factors on Dynamic Visual Acuity

Abstract

Purpose: When a target is in motion, two thresholds can be measured: dynamic visual acuity (DVA, the smallest target size at which an observer can resolve target detail) and speed threshold (the fastest target speed at which an observer can resolve target detail). Many different factors can influence DVA and speed threshold, including target trajectory, velocity, size, contrast, and colour. The limitation with research to date is that there is no standardized, validated tool with which to assess either DVA or speed thresholds. The Vision & Motor Performance Lab at the University of Waterloo School of Optometry has recently developed a distance visual acuity chart (moV&, V&MP Vision Suite) that can measure static visual acuity, DVA, and speed thresholds. moV& allows for the specifications of target trajectory, speed, size, contrast, and colour of both the target and background when measuring DVA. The primary objective of this dissertation is to examine the validity and repeatability of the high contrast (100% contrast), low contrast (61% and 20% contrast), and colour (red target on a white background and white target on a blue background) functions of moV&. If reliable, the data will then be used to examine the effect of target trajectory, speed, and size on DVA and speed threshold. Methods: Three cross-sectional studies were conducted in order to address the research objectives. Each experiment required participants to attend 2 study visits separated by a minimum of 14 days. All participants completed the static visual acuity tests before completing the dynamic tests in a randomized order. Experiment 1 (n = 25) determined the validity and repeatability of moV& using targets at 100% contrast. At each visit, static and dynamic visual acuity was measured using Snellen, ETDRS, and moV& charts. Experiment 2 determined the repeatability of the low contrast and coloured functions of moV&. Participants were assigned to either the contrast (n=21) or colour (n=21) study block. For the contrast block, low contrast (61% and 20% contrast) static and dynamic visual acuities were measured using Snellen and moV& charts. For the colour block, coloured optotype and background (red target on a white background, white target on a blue background) static and dynamic visual acuities were measured using the ETDRS and moV& charts. Experiment 3 (n = 67) examined the effect of target trajectory, speed, and size on DVA and speed threshold using the targets studied in Experiments 1-2. Data from Experiments 1 and 2 was used to determine the effect of target trajectory, speed, and size on DVA and speed threshold. A repeated measure ANOVA was used to compare static moV& visual acuity to ETDRS and Snellen charts. Test-retest reliability was determined via Lin’s correlation coefficient of concordance (CCC). Three-way ANOVA was used to determine the effect of trajectory, speed, and size on DVA and speed thresholds. Results: moV& yielded similar high contrast static visual acuity when compared to the EDTRS and Snellen charts. All high contrast static and dynamic visual acuities demonstrate good test-retest repeatability (CCCs ranged 0.451 to 0.953). moV& static visual acuities were significantly better than Snellen at both 61% and 20% contrast (p<0.05) with good repeatability (CCC61% = 0.80 and CCC20% = 0.60). CCCs for DVAs ranged from 0.05 to 0.74, but were better at 61% contrast. For the coloured targets, moV& coloured static visual acuities were significantly better than ETDRS black and white static visual acuities (p<0.05) and coloured DVA demonstrated good test-retest repeatability (CCCs ranged from 0.50 to 0.88, and were similar for both colours). Trajectory had a significant effect on dynamic visual acuity for all contrast and colour combinations, and a significant effect on speed threshold for all optotypes except the white target on a blue background (p = 0.153). Target speed had a significant effect on dynamic visual acuity for all contrast and colour combinations tested except the red target on a white background (p = 0.112), while target size had a significant effect on speed threshold for all optotypes. Discussion: moV& high contrast static visual acuity is comparable to both the Snellen and ETDRS charts. moV& static visual acuity demonstrated good repeatability for all optotypes tested. moV& DVA demonstrated good test-retest repeatability for targets at 100% contrast, red targets on a white background, and white targets on a blue background. At 61% and 20% contrast, test-retest repeatability was worse, especially at 20% contrast. Target trajectory, speed, and size have an effect on dynamic visual acuity and speed threshold, with the exception of a few optotype colour combinations. Further research is needed to explore the role of a wider range of target contrasts and colours on DVA and speed threshold.