Human error in strabismus surgery: quantification with a sensitivity analysis

Abstract

Background Reoperations are frequently necessary in strabismus surgery. The goal of this study was to analyze human-error related factors that introduce variability in the results of strabismus surgery in a systematic fashion. Methods We identified the primary factors that influence the outcome of strabismus surgery. For each of the human-error related factors we quantified variation with clinical assessments: measurement of the angle of strabismus, surgical strategy and surgical accuracy. Firstly, six patients were examined by six orthoptists, and accuracy of prism cover tests was assessed. Secondly, a questionnaire with sample cases (10°, 15°and 20°of infantile esotropia) was put to orthoptists, to determine variation in current surgical strategy. Finally, photographs made during surgery were analyzed to assess surgical accuracy. The influence of human-error related factors was related to the influence of inter-patient differences with a mechanical model. The relative contribution of all factors was assessed with a sensitivity analysis, and results were compared to clinical studies. Results The surgical trajectory of strabismus surgery could be modeled mathematically. Measurement of angle of strabismus, surgical technique, anatomy and physiology were considered. Variations in the human-error related factors were: (1) the latent angle at distant fixation was measured with a 90% confidence interval of 5°, and comprised 20% of the total variance of the postoperative angle, (2) orthoptists decided for bilateral recessions of, respectively, 7.3±1.7 mm (total amount of two recessions), 9.1±1.2 mm and 10.3±1.3 mm, which comprised 15% of the total variance, and (3) surgical accuracy was estimated at ±0.5 mm, which comprised 20% of the total variance. Conclusion The human error in strabismus surgery could be quantified with a sensitivity analysis. Approximately half of the reoperations in strabismus surgery are caused by inaccuracy in the measurement of the angle of strabismus, variability in surgical strategy and imprecise surgery.

Automated Diagnosis and Measurement of Strabismus in Children

“…8 Thus, the accuracy of measurements depends largely on the examiner's expertise and the participant's level of cooperation. [7][8][9][10]16,17 Studies showed a significant interexaminer variability in PACT among highly experienced examiners, ranging between 6.9 and 12.5 PD. 18 In this study, the interexaminer variability of the automated test was 4.25 PD, which is much lower than the variability of the manual test, which was 11.95 PD.…”

“…Consequently, this test is subject to high interexaminer variability. [7][8][9][10] In order to develop standardization and reduce the variability of manual measurements, attempts were made to develop objective automated strabismus measurement devices. These include automated image analysis software, 11 videos based on infrared eye tracking, 12 video goggles to perform a Hess screen test, 13 and binocular optical coherence tomography.…”

Inter-examiner variability and agreement of the alternate prism cover test (APCT) measurements of strabismus performed by 4 examiners

“…Several factors have been reported to play a role in the measurement of strabismus, such as examiner experience, examiner bias, positioning of the examiner and target, dissociative techniques, test being used (eg, APCT and simultaneous prism and cover test), neutralization endpoint employed, calibration and position of the prism in front of the eye, magnitude of deviation (eg, 20 PD vs420 PD), test distance, age, and type of strabismus. [1][2][3][4][5][6][7][8][9][10] A number of studies have reported inter-examiner variability and agreement in children and adults comparing 2 examiners. 1,2,8,10,11 In large eye clinics more than 2 examiners often measure the angle of deviation on a patient on separate visits.…”

A randomised comparison of bilateral recession versus unilateral recession-resection as surgery for infantile esotropia

“…The degree of alignment is subject to a large variation 19. Factors contributing to this variation are variation of the preoperative angle of strabismus, variations of measurements of the angle of strabismus, variation of the actual relocation of the muscle insertion during surgery, variation in anatomy, mechanical properties of eye muscles and other unknown parameters 3 6 13 16 19…”