Objective Evaluation of Inferior Oblique Overaction Using an Interocular Level Difference Gauge

Area of Science:

• Ophthalmology
• Strabismus Surgery
• Ocular Motility

Background:

• Inferior oblique overaction (IOOA) diagnosis traditionally relies on subjective, qualitative grading.
• This subjectivity can lead to inter-observer variability and diagnostic challenges.

Purpose of the Study:

• To introduce and pilot-evaluate a novel, objective, and quantitative measurement for IOOA.
• To assess the reliability and repeatability of the Interocular Level Difference Gauge (IOLDG).

Main Methods:

• A new device, the Interocular Level Difference Gauge (IOLDG), was designed for objective IOOA measurement.
• Sixty-two patients underwent IOOA assessment using both conventional subjective grading and the IOLDG.
• Interobserver repeatability was evaluated using paired t-tests and Intra-class Correlation Coefficients (ICC).

Main Results:

• The conventional method exhibited moderate repeatability (ICC: 0.749) and significant inter-examiner differences (p = 0.002).
• The IOLDG demonstrated excellent repeatability (ICC: 0.903, p = 0.064) and was largely independent of examiner subjectivity.
• Quantitative equivalents were established: Grade +1 = 1.04mm, Grade +2 = 1.75mm, Grade +3 = 2.81mm.

Conclusions:

• The IOLDG provides a highly repeatable, objective, and quantitative measurement for IOOA.
• This chair-side method offers superior reliability compared to conventional subjective grading scales.