Localizing Rectus Muscle Insertions

Abstract

To the editor, We congratulate Mirmohammadsadeghi et al. for their study on the use of ultrasound biomicroscopy (UBM) and the Anterior Segment Optical Coherence Tomography (ASOCT) in a cohort of patients undergoing strabismus surgery. However, this is not the first study comparing the UBM and ASOCT in locating muscle insertions. We have recently reported the feasibility and accuracy of determining the extraocular muscle insertion distance from the limbus in previously operated extraocular muscles with the swept-source ASOCT and compared with wide-field UBM. The technique and expertise when using both the instruments must be stressed. In the present study, two operators were doing the two measurements; hence, additional masked interpreters of both images could have strengthened the study. Intraclass correlations could be obtained to make sure one operator was not better than the other or the ease of identifying the muscle insertion could be compared with the same operator doing both measurements. Eye position and degree of head rotation might influence the measurements, and maximum rotation might provide the best delineation. Hence, the degree of rotation can also be standardized. The authors have not mentioned what gel they used as a coupling medium. The clear scan (Clear Scan (ClearScan® Ultrasound Cover CS200, ESI Inc, USA)) or any other sterile disposable cover, is the most comfortable to use without the cup and can image increasing distances, in our experience (No financial interest). The intraoperative caliper measures precisely up to 1 mm, so an estimation of 0.5 mm on the caliper, can be a limitation. The farthest distance measured by the machines is 8.5 and 9.3 mm. We would like to know whether this measurement was of primary or re-operated muscles as the measures are much less than that reported in the literature. The authors mention that five measures on ASOCT were within 1–1.5 mm. This number is very high, so what do the authors speculate about the reason for this variability? Could the authors tell us which muscle (MR/LR) is being referred to when comparing measurements between esotropia and exotropia. We presume the figure shown by the author was that of primary surgery; and we would like to know how did the operators find the delineation of insertions in reoperations? It is important to note that the utility of these instruments is diminutive in cases of primary strabismus surgeries. Hence, more qualitative and quantitative information is required about the measurements in reoperations. The three cases of reoperations reported by the authors do add to the limited literature in this area. We achieved an accuracy of 69% of imaging insertions within 1 mm vs. 38% by the UBM in cases of reoperations. We need more studies in a more significant number of reoperations to expand the utility of the ASOCT. The current evidence indicates that the ASOCT identifies the muscle insertion distance more accurately than UBM, more so in reoperations besides being noncontact and having high patient comfort. The paper by Mirmohammadsadeghi et al. is a valuable addition to the research in this area.