Both objective and subjective methods of measuring cyclodeviation are important for diagnosing and managing strabismus. Objective measurements involve evaluating the fundus to identify the anatomical position of the eyes while subjective measurements, such as the double Maddox rod (DMR), rely on the patient’s perception of the cyclodeviation. However, few studies have compared DMR with other methods of cyclodeviation testing. A new study in the American Journal of Ophthalmology compares the DMR to other measurements of cyclodeviation and has found good agreement between DMR, largest single Maddox and synoptophore cross in circle.

In a retrospective cohort study, DMR was compared with several other methods of cyclodeviation. Researchers looked at 153 adults who had already been diagnosed with strabismus via DMR and another method of cyclodeviation determination. In addition, DMR patients received at least 1 of the following: fusable synoptophore targets (105 patients), non-fusable synoptophore targets (73 patients), single Maddox rod (118 patients), and fundus photography (54 patients). Mean values were calculated based on single measurements for all tests except DMR, where, if 3 measures were available, a mean was taken.

The researchers then compared the results by calculating the mean difference, 95% confidence intervals, interclass coefficients (ICC), and Bland-Altman plots with linear regression. Researchers found that synoptophore cross in circle targets, or the non-fusable targets, and DMR yielded similar values with a mean difference of 1.2 and ICC of 0.79. Likewise, good agreement was found between single Maddox rod values and DMR with a mean difference of 0.1 degrees and ICC of 0.82. Mean summed single Maddox rod values were also similar to DMR with a mean difference of 1.5 degrees and ICC of 0.85. However, it was noted that differences increased with greater degrees of cyclodeviation (P <.001). Meanwhile, synoptophore house targets, fusable targets, measured a larger excyclodeviation with a mean difference of -2.7 degrees and ICC of 0.71.


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When comparing fundus photography with DMR, researchers found a large, uncorrelated difference both when summing up the right and left eye, with a mean difference of 12.2  degrees and ICC of -0.02, and when using the largest of right and left, with a mean difference of 6.2 degrees with ICC of – 0.21. The difference increased with greater cyclodeviation.

While there is good agreement between MDR, single Maddox rod, and synoptophore cross in circle, researchers note that further is needed to identify which measurement best reflects true cyclodeviation. 

References

Lepor L, Hatt S, Leske D, Klaehn L, Kramer A, Holmes J. Comparison of methods for measuring cyclodeviation. Am J Ophthalmol. Published online November 27, 2020. doi:10.1016/j.ajo.2020.11.005