Objective Evaluation of Inferior Oblique Overaction Using an Interocular Level Difference Gauge
- Author:
Hong Won LEE
1
;
Il DOH
;
Yeon-Hee LEE
Author Information
- Publication Type:Original Article
- From:Korean Journal of Ophthalmology 2026;40(1):63-69
- CountryRepublic of Korea
- Language:English
-
Abstract:
Purpose:The conventional method for evaluating inferior oblique overaction (IOOA) relies on subjective, qualitative grading. This study aimed to introduce and perform a pilot evaluation of a novel, objective, and quantitative measurement method for IOOA using a newly designed device, the interocular level difference gauge (IOLDG).
Methods:Sixty-two consecutive patients (124 eyes) with intermittent exotropia, IOOA or superior oblique palsy were recruited. The degree of IOOA was measured using two methods: (1) the conventional subjective grading scale (+0 to +4) by two examiners (A and B); and (2) the objective IOLDG method by two examiners (C and D). The IOLDG utilizes a spectacle-like frame with a 1 mm-spaced horizontal grid to measure the interocular height difference of the inferior corneal margin in millimeters. Interobserver repeatability was assessed using the paired t-test and the intraclass correlation coefficient (ICC).
Results:The conventional method showed a statistically significant difference between examiners (paired t-test, p = 0.002) and moderate repeatability (ICC, 0.749). In contrast, the IOLDG method showed no significant difference between examiners (paired t-test, p = 0.064) and demonstrated excellent repeatability (ICC, 0.903; p < 0.001). The correlation analysis established quantitative equivalents for the conventional grades: grade +1 corresponded to 1.04 ± 0.75 mm, grade +2 to 1.75 ± 0.60 mm, and grade +3 to 2.81 ± 0.75 mm.
Conclusions:The IOLDG provides a highly repeatable, objective, and quantitative measurement for IOOA, largely independent of the examiner’s subjective judgment. This simple, chair-side method offers superior reliability compared to the conventional grading scale.
