The effect of Bangerter filters on optotype acuity, Vernier acuity, and contrast sensitivity

Abstract

Purpose Bangerter filters are designed to cause progressive degradation of distance optotype acuity to predicted levels (density label indicating expected decimal acuity) and are used to treat amblyopia and diplopia. Nevertheless, there are few data reporting induced acuity deficits. We investigated the effect of Bangerter filters on distance and near optotype acuity, vernier acuity, and contrast sensitivity. Methods Fifteen subjects with best corrected optotype acuity of at least 20/25 in each eye were blurred sequentially in one eye with 7 Bangerter filters (densities <0.1, 0.1, 0.2, 0.3, 0.4, 0.8, 1.0). At each filter level distance and near optotype acuity (LogMAR), vernier acuity and contrast sensitivity were assessed. Mean log acuities were compared using generalized estimating equation methods. Results The 1.0, 0.8, and 0.4 filters degraded distance optotype acuity to a similar degree (mean 0.22, 0.23, and 0.28 logMAR). Subsequent filters progressively degraded acuity: 0.44, 0.57, 0.93, 1.69 logMAR. Near optotype acuity was reduced in a similar pattern. Vernier acuity was minimally degraded by 1.0, 0.8, and 0.4 filters (18, 19, and 20 arcsec), followed by progressive degradation with subsequent filters (31, 35, 113, and 387 arcsec). Contrast sensitivity was minimally reduced with filters 1.0 through 0.2, and then precipitously degraded with 0.1 and <0.1 filters. Conclusion The 1.0, 0.8, and 0.4 filters cause similar, minimal degradation of distance and near optotype, and vernier acuity, whereas subsequent filters cause progressive degradation. Contrast sensitivity is not markedly reduced until the 0.1 filter. These results have important implications for using Bangerter filters therapeutically.

Does Partial Occlusion Promote Normal Binocular Function?

“…These decrements were on the order of 0.3 logMAR with the 0.2 filter producing a greater deficit of approximately 0.55 logMAR. These results are consistent with previous reports indicating that the midrange filters have very similar 23 and, in some cases, nonmonotonic 21 effects on visual acuity. We found a very similar pattern of results for vernier acuity and, in agreement with previous work, 22,23 the decrement in acuity was correlated with the decrement in vernier acuity suggesting a common action of the microelements within the filters on these two visual functions.…”

“…These results are consistent with previous reports indicating that the midrange filters have very similar 23 and, in some cases, nonmonotonic 21 effects on visual acuity. We found a very similar pattern of results for vernier acuity and, in agreement with previous work, 22,23 the decrement in acuity was correlated with the decrement in vernier acuity suggesting a common action of the microelements within the filters on these two visual functions. Importantly, our results for the effect of the 0.2 strength filter on visual acuity are in direct agreement with those found by Rutstein et al 24 who also reported an average visual acuity of 0.55 logMAR (equivalent to 20/71) when children with amblyopia viewed through a 0.2 filter using their nonamblyopic eye.…”

“…We chose this acuity-based metric as the strength of monocular partial occlusion for amblyopia therapy is based on the rationale that acuity in the fixing eye should be reduced below that of the fellow amblyopic eye. 20 Due to the inherent variability between Bangerter filters of the same nominal strength, 21,23,24 we first fully characterized our batch of filters in terms of their effects on monocular performance measures including acuity, contrast sensitivity, and vernier acuity prior to measuring the effects on binocular function.…”

“…Clinical (Worth-4-dot) and psychophysical measurements of suppression as well as measurements of stereopsis were assessed under partial occlusion conditions induced by a Bangerter filter, optical defocus, or an ND filter. Because the effect of Bangerter filters on visual acuity does not vary reliably with increasing filter density, 23 we selected levels of optical blur and ND filter strength by matching their effects on monocular acuity to those of the Bangerter filters. Specifically, for each participant, we measured monocular acuity for each strength of Bangerter filter.…”

Emergence of categorical face perception after extended early-onset blindness

“…They were tested while wearing blur goggles simulating Snellen visual acuities of 20/300, 20/600, and 20/800 (nonoverlapping groups of 10 children at each blur level). Blurring was achieved by attaching Bangerter Occlusion foils (40) to clear safety goggles. Assessing the performance of normally sighted subjects while they were wearing blurring goggles enabled us to titrate the effects of reduced acuity comparable to the Prakash children's postoperative outcomes, separate from nonoptical factors on face classification performance.…”