We read the article “Ocular Torsion among Patients with Intermittent Exotropia: Relationships with Disease Severity Factors,” by Shin and associates, with interest. We would like to congratulate the authors on this excellent study. It is a laudable attempt to study a factor that, hitherto, has not been evaluated in purely horizontal deviations with no patterns. This study explored a new avenue that may change our current understanding of the fusional mechanisms in intermittent exotropia. However, we have the following comments regarding the methodology and interpretation of the results.
Previous studies have reported the extent of fundal torsion to be up to 12.5 degrees in normal subjects. Taking this into account, we believe that few of the present study subjects, in both the control group and the intermittent exotropia group, also could have a normal range of fundal torsion, which would confound the study results. Therefore, it may be more appropriate to exclude patients within this normal range and then reanalyze the data to determine if there is any statistically significant difference between the 2 groups.
Also, the authors found that the status of ocular torsion had a strong correlation with the severity of exotropia and the degree of stereopsis. The severity of exotropia was calculated by taking into consideration factors such as distance angle of exotropia, Titmus stereoacuity, and duration of strabismus. However, in intermittent exotropia, it is well known that the actual control of the patient over the exodeviation is a more relevant clinical measure of the severity of the deviation, rather than the numerical angle of the deviation. Therefore, a subjective grading of the degree of control for distance and near using a scale such as the Newcastle scoring system, in addition to the measurement of the angle, may have been more appropriate. Also, in intermittent exotropia, stereopsis for near remains largely unaffected until the deviation is almost constant or the subject has a very poor control for near fixation; therefore, measuring the distance stereopsis is considered to be a more accurate measure of deterioration of fusional control in these cases. Hence, the correlation of near stereopsis with the state of torsion, as measured in this study, may not be clinically significant.