A Convenient Method to Estimate Alignment of Eyes Under General Anesthesia in Strabismus Subjects

<b>Introduction:</b> This study aims to describe an objective and simple method to estimate the alignment of eyes under general anesthesia (GA) in strabismus subjects, which may vary from the angle measured preoperatively.<b>Materials and Methods:</b> Through the operating microscope, pictures of the eye position of 94 subjects with horizontal strabismus were captured under GA. A curved caliper was placed parallel to the horizontal meridian, and the distance between the center of cornea and the corneal reflex spot of the microscope was measured. The eye position was estimated with a quantified Hirschberg method for each eye, and the values were added to reflect the global binocular angle of deviation. To validate this method, four strabismus surgeons blindly evaluated the strabismus angle based on these pictures, and the results were compared. Agreement between the four measurements was estimated using the ICC (Intraclass Correlation Coefficient) index.<b>Results:</b> ICC coefficients and their 95% confidence interval were 0.93 (0.88-0.95) for the overall angle, 0.91 (0.89-0.94) for the right eye and 0.86 (0.77-0.91) for the left eye, indicating good to excellent reliability of these measurements.<b>Conclusion:</b> Evaluating the evolution of the strabismus under GA may be of clinical interest and have potential therapeutical consequences. The described technique is fast, convenient, and reliable and provides a tool to encourage surgeons to take into account this parameter of strabismus.