Variation in the degradation of stereoacuity via monocular blur across multiple stereotests

Purpose: Detecting changes in stereothresholds aids in the diagnosis and management of binocular vision disorders. However, there is variation in the stereoacuity levels measured across a range of stereotests. There are limited data assessing how stereotests respond to degradations of stereoacuity. Therefore, the aim of this study is to compare stereothresholds obtained from four different stereotests across different conditions of induced monocular blur. Methods: Stereoacuity was measured once for each Bangerter foil condition (no foil, 0.2 foil, 0.4 foil) using the Frisby, TNO, Lang-Stereopad and Asteroid stereotests. Inclusion criteria were age ≥18 years, no history of conditions that could impair stereoacuity, best-corrected monocular visual acuity of equal to or better than 0.3 logMAR, an interocular difference of less than 0.2 logMAR, up to date refractive correction (within the last 2 years) if required, and the ability to provide informed written consent. Significance of the differences in values between tests was calculated using the Kruskal-Wallis test, with further pairwise comparisons made via post-hoc analysis. Results: Fifty-one visually normal adults (67% female) of mean age 25 years ±8.35 were included. Statistically significant differences were achieved for most pairwise comparisons (p < .05), except when comparing TNO and Asteroid. The TNO and Lang-Stereopad tests degraded by the same median values between foil conditions, with Frisby showing the least median change between foils (0.135 median difference between 0.2 and 0.4 foils, p < .001). Conclusions: Stereotests detect stereoacuity degradation to varying extents, with the Asteroid test being most sensitive to change via monocular blur. The reasons for these differences lie in the varying methods of presentation. It is therefore recommended that test selection remains constant between appointments for the purpose of assessing subtle changes to aid patient management. Further evaluation of the ability to detect alterations in stereothresholds is required in people with impaired stereoacuity.