Accuracy of Double Maddox Rod with Induced Hypertropia in Normal Subjects

Abstract

Background and Purpose

The double Maddox rod is a commonly used instrument to test for cyclotorsion in the clinical setting. This paper assesses the ability of patients without torsional complaint to accurately demonstrate torsional status with varying degrees of induced hypertropia as tested by double Maddox rod.

Methods

Thirty-seven orthophoric subjects underwent double Maddox rod testing with vertical prism of 3^Δ, 10^Δ, 16^Δ, 20^Δ, and 30^Δ. Subjective torsion was recorded for each prism diopter.

Results

Mean subjective torsion was recorded as 0.95°, 1.6°, 1.9°, 2.1°, and 2.2° for 3^Δ, 10^Δ, 16^Δ, 20^Δ, and 30^Δ, respectively. Torsion increased in a logarithmic manner as modeled by R™ software version 2.15.2.

Conclusions

The double Maddox rod test as commonly used in clinical practice is both subjective and prone to administrator and subject error. Subjects have more difficulty properly aligning the double Maddox rod as distance between images is increased. It is also possible that recruitment of the oblique muscles during attempted vertical fusion leads to subjective torsion during double Maddox rod testing in otherwise normal participants.

• Double Maddox rod
• torsion
• hypertropia