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Lily Yu-Li Chang, Peng Guo, Ben Thompson, Mehrdad Sangi, Jason Turuwhenua; Assessing visual acuity – test-retest repeatability and level of agreement between the electronic ETDRS chart (E-ETDRS), optokinetic nystagmus (OKN), and sweep VEP. Invest. Ophthalmol. Vis. Sci. 2018;59(9):5789.
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The gold standard measure of visual acuity (VA), the ETDRS chart, relies on subjective patient responses. This can result in low testability in children and patients with cognitive impairment. Objective measures of VA may solve this problem. We investigated the use of objective VA measures (OKN and sweep VEP) in healthy adults. Our hypotheses were 1) objective methods would have high test-retest repeatability, and 2) VA results would be strongly correlated across the different techniques.
Monocular unaided visual acuity was measured for each eye in 10 healthy adult participants (21.9 ±1.10 years, mean spherical equivalent, -0.71 ±1.28 DS), using E-ETDRS (Jaeb Center for Health Research, USA), OKN (bull’s eye stimulus array with stroke widths equivalent to logMAR 1.0-0.0 in 0.1 steps, 5 trials per logMAR level, stimulus speed 7 deg/s), and sweep VEP (Roland Consult, Havel, Germany). E-ETDRS and sweep VEP both provided a numerical logMAR output. OKN videos were analysed trial by trial, using a mixed subjective (judged by clinical observer) and objective (image processing) protocol. OKN was judged to be present or absent on each trial. Test-retest repeatability and correlations were assessed using Spearman’s Rho because data were non-parametric.
Test and retest measures were strongly correlated within each technique, with the highest correlation being for OKN (r=0.959, p<0.01. Mean logMAR for test +0.31±0.26 vs. retest +0.28±0.27) followed by E-ETDRS (r=0.928, p<0.01. Mean logMAR for test +0.27±0.41 vs. retest +0.25±0.41) and sweep VEP (r = 0.882, p<0.01. Mean logMAR for test +0.10±0.40 vs. retest +0.20±0.34). The OKN VA measure was strongly correlated with the E-ETDRS measure (r=0.865 p<0.01). The sweep VEP measure was not correlated with E-ETDRS (r=0.220, p>0.05).
In healthy adult participants, test retest repeatability was high for all three techniques. Visual acuity measurements by OKN had the best test retest repeatability, and OKN measures were strongly correlated with E-ETDRS measures. Objective measurement of VA has a role in clinical testing, and further investigation of the OKN technique is warranted in populations that can be challenging to test using ETDRS, such as preverbal children and patients with dementia.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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