Purpose To establish the thresholds for “real change” in stereoacuity by defining long term test-retest variability as 95% limits of agreement for four stereoacuity tests. Design Retrospective cohort study. Participants and/or Controls We identified 36 patients (median age 17 years, range 7 to 76 years) with any type of stable strabismus who had stereoacuity measured on two consecutive visits. Stable strabismus was defined as angle of deviation within 5 prism diopters (pd) by simultaneous prism and cover test (SPCT) and prism and alternating cover test (PACT). Methods Stereoacuity was measured at near using the Preschool Randot and the near Frisby stereotests and at distance using the Frisby Davis Distance (FD2) and the Distance Randot stereotests. Stereoacuity was transformed to log units for analysis. 95% limits of agreement were calculated based on a 1.96 multiple of the standard deviation of differences between test and retest. Main Outcome Measures 95% limits of agreement for change in stereoacuity thresholds at two consecutive visits. Results 95% limits of agreement were 0.59 log arcsec for the Preschool Randot, 0.24 for the near Frisby, 0.68 for the FD2, and 0.46 for the Distance Randot. These values correspond to the following octave steps (doublings of threshold; for example, 200 to 400 arcsec): Preschool Randot 1.95, near Frisby 0.78, FD2 2.27, and Distance Randot 1.52. Conclusions A change of approximately two octaves of stereoacuity threshold are needed to exceed test-retest variability for most stereoacuity tests. Changes less than two octaves cannot be distinguished from test-retest variability. When used to guide patient management, caution should be taken in interpreting changes in stereoacuity of less than two octaves.

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.

Purpose To determine the effect of induced monocular blur on stereoacuity measured using ‘real depth’ and ‘random dot’ tests. Methods Monocular visual acuity deficits (range 20/15 to 20/1600) were induced with 7 different Bangerter filters (<0.1, 0.1, 0.2, 0.3, 0.4, 0.8, and 1.0) in 15 visually normal adults. Stereoacuity was measured using Frisby and Frisby Davis Distance (FD2) ‘real depth’ tests and Preschool Randot (PSR) and Distance Randot (DR) ‘random dot’ tests. Stereoacuity results were grouped as either ‘fine’ (≤60 arcsec), ‘moderate’ (>60 and ≤200 arcsec), or ‘coarse/nil’ (>200 arcsec to nil) stereo. Results Across visual acuity deficits, stereoacuity was more severely degraded with random dot (PSR, DR) than with real depth (Frisby, FD2) tests. Degradation to ‘worse than fine’ stereoacuity consistently occurred at 0.7 logMAR (20/100) or worse for Frisby, 0.1 logMAR (20/25) or worse for PSR, 0.1 logMAR (20/25) or worse for FD2. There was no meaningful threshold for the DR since ‘worse than fine’ stereoacuity was associated with −0.1 logMAR (20/15). Course/nil stereoacuity was consistently associated with 1.2 logMAR (20/320) or worse for Frisby, 0.8 logMAR (20/125) or worse for PSR, 1.1 logMAR (20/250) or worse for FD2, and 0.5 logMAR (20/63) or worse for DR. Conclusions Stereoacuity thresholds are more easily degraded by reduced monocular visual acuity using random dot tests (PSR and DR) than real depth tests (Frisby and FD2). We have defined levels of monocular visual acuity degradation associated with ‘fine’ and ‘nil’ stereoacuity. These findings have important implications for testing stereoacuity in clinical populations.

Editorial group: Cochrane Eyes and Vision Group. Publication status and date: New search for studies and content updated (no change to conclusions), published in Issue 1, 2010.

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