The effect of induced monocular blur by bangerter filters on measures of visual acuity and stereoacuity

To evaluate the effect of monocular blur induced by Bangerter filters (BF) on visual acuity (VA) and stereoacuity. Monocular blur was induced by a range of Trusetal BF strengths (0.1, 0.2, 0.4, 0.6) to 23 visually normal adult volunteers (aged 18-25, mean age 20.33 ± 1.79 years). The right monocular and binocular logMAR VA and distance stereoacuity using the FD2 were measured at 6 m with no filter (baseline) and with each filter strength. The order of testing the filters was randomized. Results were analyzed using one factor repeated measures ANOVAs, t-tests using Bonferroni correction and Pearson's product moment correlation. All filters degraded right monocular distance VA from baseline, but less significantly between the 0.4 and 0.6 filters than the other filters (p < .05 and p < .001, respectively). Degradation was in concordance with the labeled filter density, excluding filter strength 0.4. For all filter strengths, binocular VA was significantly but not clinically reduced from baseline (p < .05). Filters statistically and clinically significantly degraded distance stereoacuity from baseline (p < .001). A significant negative correlation existed between the mean degraded right monocular VA and stereoacuity (r = -0.998, p < .02). Trusetal BF significantly reduced monocular VA and stereoacuity but binocular VA remained within normal levels. The impact on VA and stereoacuity in a normal population can be of clinical relevance when applied to the use of BF for management of amblyopia and intractable diplopia. It is advised that clinicians ensure the desired level of degradation has been achieved in clinic before prescribing a particular filter strength.