Observer Variability in Assessing Passive Cyclorotation using Guyton’s Exaggerated Traction Test Before Strabismus Surgery
Tobias E. Torp-Pedersen; Claes S. Loenkvist; Jon Peiter Saunte
Department of Ophthalmology, Rigshospitalet Glostrup
Introduction: As an aid in planning strabismus surgery, we routinely perform Guyton´s exaggerated traction test (ETT) with retroplacement and passive excyclorotation and incyclorotation with forceps for evaluating tension of the superior and inferior oblique muscles, respectively. The purpose of this study was to investigate observer variability in this test.
Methods: Three experienced strabismus surgeons performed individual bilateral ETT on 30 eyes of 15 consecutive patients undergoing strabismus surgery in general anaesthesia. These measurements were compared with the same test using a protractor on the cornea (gold standard). We defined agreement as a deviation of at most 10 and 15 degrees from gold standard for exyclorotation and incyclorotation, respectively.
Results: We found no significant differences in measurements between observers. Observer measurement agreed with gold standard in 81% and 89% of cases for excyclorotation and incyclorotation, respectively. Mean deviation from gold standard for excyclorotation was an underestimation of 3° (95% confidence interval [CI] -17° to 24°). Mean deviation from incyclorotation was an overestimation of 6° (95% CI -19° to 30°).
Discussion: While Guyton´s exaggerated traction test is an excellent test for evaluating tension of the oblique muscles, we found that individual observers agreed less than expected with the gold standard performed with a protractor.
Conclusion: We believe that the present results illustrate the need for an objective measurement in the exaggerated traction test.
References: Guyton DL. Exaggerated traction test for the oblique muscles. Ophthalmology. 1981;Oct;88(10):1035-40.