Defining real change in prism-cover test measurements.
OBJECTIVE
To describe the interobserver test-retest variability of both simultaneous prism and cover testing (SPCT) and alternate prism and cover testing (APCT) in horizontal deviations, and to calculate 95% limits of agreement that might be used to define real change.


METHODS
Prospective cohort study.


METHODS
Twenty-three patients with sixth nerve palsy and three controls were independently examined by two experienced strabismus surgeons. SPCT and APCT were performed at distance and near fixation. Test-retest variability and agreement between tests were evaluated using Bland-Altman plots and 95% limits of agreement were calculated.


RESULTS
For SPCT, the 95% limits of agreement half-widths were 6.3 prism diopters (pd) at distance fixation and 6.9 pd at near. For APCT, the 95% limits of agreement half-widths were 10.2 pd at distance and 9.2 pd at near.


CONCLUSIONS
Based on 95% limits of agreement half-widths between two examiners, a change in strabismus measurements of less than 10 pd may be attributable to test-retest variability. Changes of 10 pd or more are likely to represent real change and might be used as the threshold for management decisions.
Holmes
Jonathan M
JM
Department of Ophthalmology, Mayo Clinic, College of Medicine, 200 First Street SW, Rochester, MN 55905, USA. holmes.jonathan@mayo.edu
Leske
David A
DA
Hohberger
George G
GG
D020434:Abducens Nerve Diseases / Q000175:diagnosis*; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003941:Diagnostic Techniques, Ophthalmological; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D009801:Oculomotor Muscles / Q000473:pathology*; D011446:Prospective Studies; D013285:Strabismus / Q000175:diagnosis*