Elsevier

Ophthalmology

Volume 116, Issue 2, February 2009, Pages 281-285
Ophthalmology

Original article
Defining Real Change in Measures of Stereoacuity

https://doi.org/10.1016/j.ophtha.2008.09.012Get rights and content

Purpose

To establish the thresholds for “real change” in stereoacuity by defining long-term test–retest variability as 95% limits of agreement for 4 stereoacuity tests.

Participants and Controls

We identified 36 patients (median, 17 years; range, 7–76) with any type of stable strabismus who had stereoacuity measured on 2 consecutive visits. Stable strabismus was defined as angle of deviation within 5 prism diopters by simultaneous prism and cover test and prism and alternating cover test.

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. The 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

The 95% limits of agreement for change in stereoacuity thresholds at 2 consecutive visits.

Results

The 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 with the following octave steps (doublings of threshold; e.g., 200–400 arcsec): preschool Randot, 1.95; near Frisby, 0.78; FD2, 2.27; and distance Randot, 1.52.

Conclusions

A change of approximately 2 octaves of stereoacuity threshold are needed to exceed test–retest variability for most stereoacuity tests. Changes <2 octaves cannot be distinguished from test–retest variability. When used to guide patient management, caution should be taken in interpreting changes in stereoacuity of <2 octaves.

Financial Disclosure(s)

The authors have no proprietary or commercial interest in any materials discussed in this article.

Section snippets

Subjects and Methods

Institutional Review Board approval was obtained for this study. All experiments and data collection were conducted in a manner compliant with the Health Insurance Portability and Accountability Act.

Results

The 95% limits of agreement are summarized in Table 1 and represented on the Bland–Altman plots in Figure 1(A–D). The Bland–Altman plots suggest that, for each stereoacuity test, magnitude of the test–retest differences did not seem to be dependent on the level of stereoacuity (Fig 1A–D). When converting the log values of the 95% limits of agreement back to octave steps (doublings) of stereoacuity, the half width of the 95% limit of agreement for the preschool Randot was 1.95 octaves; for the

Discussion

In our study of test–retest variability over time using 4 current stereoacuity tests, patients with stable strabismus and stable visual acuity showed marked variability of stereoacuity thresholds. We found that for most tests a change of ≥2 octaves (doublings) is needed for change to exceed test–retest variability. Changes that exceed test–retest variability are likely to represent real changes.

Stereoacuity thresholds are often used in clinical practice as a guide to management. If stereoacuity

References (18)

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Manuscript no. 2008-626.

Financial Disclosure(s): The authors have no proprietary or commercial interest in any materials discussed in this article.

Supported by National Institutes of Health Grants EY015799 (JMH); Research to Prevent Blindness, Inc., New York, NY (JMH as Olga Keith Weiss Scholar and an unrestricted grant to the Department of Ophthalmology, Mayo Clinic), and Mayo Foundation, Rochester, Minnesota.

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