Validity and Reliability of 2 Cirrus Optical Coherence Tomography Procedures for Measuring Objective Ocular Torsion

Torsional eye position by the disc-fovea angle (DFA) is a relevant objective parameter in vertical strabismus. DFA measurement with optical coherence tomography (OCT) has proven to be a good alternative to the gold standard measurement in fundus photography. Our study aims to analyze the validity and reliability of 2 undescribed Cirrus high-definition OCT (HD-OCT; Carl Zeiss Meditec) methods that offer clinical advantages for measuring objective cycloposition in normal patients compared with Spectralis spectral-domain OCT (Heidelberg Engineering) and the reference method.

Prospective validity and reliability analysis.

Objective cycloposition by means of the DFA was measured in the right eyes of 59 binocularly normal individuals attending the ophthalmology service of a medical institution. DFA was obtained by fundus photography (gold standard), FoDi software of Spectralis spectral-domain OCT, HD 1 line scan of Cirrus HD-OCT, and macular cube of Cirrus HD-OCT (fundus, FoDi, line, and cube methods, respectively). Measurements were performed 3 times for each method and the patient was repositioned and realigned between captures. Posterior manual quantification was made by 2 observers with external protractor software for the fundus and cube methods.

The 3 OCT methods showed and excellent agreement with fundus photography (ICC 0.83-0.84) with no significant differences comparing mean values (P = .36 for fundus-FoDi, P = .09 for fundus-line, and P = .09 for fundus-cube). Absolute differences between methods were 1.5°. All methods showed excellent reliability (ICC 0.92 for FoDi, 0.91 for line, 0.92 for cube, and 0.91 for fundus). The minimal detectable change was lower than 3° and the absolute difference between repeated measurements was 1° for all methods. Interrater reliability was excellent for methods requiring manual quantification (ICC 0.98 for cube, ICC 0.94 for fundus).

Measurement of the DFA by Cirrus HD-OCT methods in normal patients was a valid and reliable alternative for the cycloposition assessment. Among the methods, the Cirrus OCT HD 1 line improved clinical performance due to the simplicity and speed of measurement, with no need to export the image for quantification.