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Defining real change in prism-cover test measurements
Jonathan M Holmes1, David A Leske, George G Hohberger
1Department of Ophthalmology, Mayo Clinic, College of Medicine, 200 First Street SW, Rochester, MN 55905, USA. holmes.jonathan@mayo.edu
American Journal of Ophthalmology
|November 30, 2007
Summary
Interobserver variability in strabismus testing was assessed using simultaneous prism and cover testing (SPCT) and alternate prism and cover testing (APCT). Changes of 10 prism diopters or more likely indicate real changes in horizontal deviations.
Area of Science:
- Ophthalmology
- Strabismology
- Clinical Measurement
Background:
- Accurate measurement of horizontal deviations is crucial for managing strabismus.
- Understanding test-retest variability is essential for interpreting changes in measurements.
Purpose of the Study:
- To evaluate the interobserver test-retest variability of simultaneous prism and cover testing (SPCT) and alternate prism and cover testing (APCT).
- To establish 95% limits of agreement for these tests to define clinically significant changes in horizontal deviations.
Main Methods:
- Prospective cohort study involving 23 patients with sixth nerve palsy and 3 controls.
- Two experienced strabismus surgeons independently performed SPCT and APCT at distance and near fixation.
- Bland-Altman plots were used to calculate 95% limits of agreement.
Main Results:
- The 95% limits of agreement half-widths for SPCT were 6.3 prism diopters (pd) at distance and 6.9 pd at near.
- The 95% limits of agreement half-widths for APCT were 10.2 pd at distance and 9.2 pd at near.
Conclusions:
- A change of less than 10 pd in strabismus measurements may be due to test-retest variability.
- Changes of 10 pd or more are likely real and can serve as a threshold for management decisions.
