Effect of monocular impaired visual acuity across Optonet^TM and non-digital clinical stereotests

Background: Impaired depth perception can be caused by monocular blur and is assessed with a range of stereotests, but differences in test presentation result in varying outcomes. A new testing system Optonet includes a stereo test which has not been evaluated in terms of the impact of blur; therefore, the aim of this study was to compare the effect of simulated impaired visual acuity across differing stereotests including Optonet. Method: Participants aged ≥18 years with visual acuity ≤0.3 logMAR in either eye and <0.2 logMAR interocular difference were included. Visual acuity (VA) was tested using the ETDRS test for near (40cms) and distance (4 meters). Stereoacuity was measured with Frisby, TNO, and Optonet, a random dot-based test on an iPad with red/blue glasses. Blur was induced with Bangerter foils 0.2 and 0.4 and VA and stereodata were remeasured. An arbitrary value of 5000" of arc was given if stereoacuity was not measurable. Results: Twenty-five participants (23 females and 2 males), median age 21 (IQR:2, Range 19-38), were included. Near VA (Median ± IQR) with 0.2 and 0.4 Bangerter foil (right eye) was 0.36 ± 0.18 and 0.50 ± 0.19 logMAR, respectively, with 0.00 ± 0.15 logMAR in left eye. TNO demonstrated the largest degradation compared to Frisby and Optonet (no foil: 60" (TNO) 20" (Frisby) 40" (Optonet), 0.2 foil: 240" (TNO) 40" (Frisby) 119" (Optonet), 0.4 foil: 2000" (TNO) 85" (Frisby) 158" (Optonet)). Significant differences in the amount that stereoacuity was reduced occurred between Frisby and TNO (p < .05, Friedman's two-way analysis of variance). Conclusion: Differences in stereoacuity are evident across stereotests under simulated conditions of blur. For accurate repeatable measures of stereoacuity, a consistent stereotest should be used. Random dot tests such as TNO and Optonet are impacted more by blur than Frisby with Optonet showing the greatest sensitivity to blur.