Assessment of interlinked double staircase acuity test

Abstract

PurposeTo compare a novel visual acuity threshold algorithm using a predictive double staircase method with standard ETDRS logMAR chart.MethodsSoftware was written in MATLAB to generate a computerised visual acuity test. The algorithm uses a randomly presented double staircase method, the staircases are interlinked using a prediction of threshold based on each prior response. This reduces test duration and increases accuracy. The screen was calibrated using a Vernier scale and there solution of the test was 0.02 log units. Ten threshold measurements were made for each test, the results expressed as the mean and standard deviation. The test was performed by three observers each with an induced range of refractive errors and compared with the result ofETDRS logMAR acuity using a chart generated with the same screen calibration.ResultsMean stair cased acuities were −0.13, 0.02, 0.22, 0.36, 0.56 log unitsfor 0, 0.5, 1, 1.5 and 2 dioptres of defocus respectively. The mean single letter score logMAR acuities were −0.08, 0.01, 0.17, 0.38, 0.58 log units. The mean error in the stair cased test was 0.02 (SD 0.01) log units forall defocus values. The mean difference between the two tests was −0.01 log units (SD 0.09). Bland‐Altmann plots showed no systematic difference. The mean time to perform the staircased test was 93 seconds (SD 19s).ConclusionsThe interlinked double staircase method gives a fast and accurate assessment of visual acuity which compares well with ETDRS logMAR.Ten threshold measures allow error estimation which is not available in a logMAR test. Other advantages over logMAR include a true resolution of 0.02 log units rather than interpolation and random letter generation with no memory effect.