Received 21 May 2008; received in revised form 22 August 2008; accepted 7 September 2008. published online 16 December 2008.
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.
Design
Retrospective cohort study.
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.
Available online: December 16, 2008.
Department of Ophthalmology, Mayo Clinic, Rochester, Minnesota
Correspondence: Dr Jonathan M. Holmes, Ophthalmology W7, Mayo Clinic, Rochester, MN 55905. Fax: (507) 284-8566
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.
ABSTRACT