Evaluation of the Ultrasound Biomicroscope in Strabismus Surgery Patrick Watts, MBBS, MS, FRCOphth, a,b David Smith, MD, CM, FRCSC, a,b Leslie MacKeen, BSc, a Stephen Kraft, MD, FRCSC, a,b J. Raymond Buncic, MD, FRCSC, a,b and Mohamed Abdolell, MSc c,d Purpose: This study was done to determine the ability of the ultrasound biomicroscope (UBM) to define the distance of the horizontal extraocular muscle insertions from the limbus in children undergoing strabismus surgery. Methods: A total of 51 children undergoing primary surgery on their horizontal muscles were recruited for this study. The 50 MHz UBM was used before surgery on the muscle(s) requiring an operation to define the distance of the insertion of the horizontal rectus muscle(s) from the limbus. These data were stored on a computer and masked from the surgeon who measured the actual insertion from the limbus with calipers intraoperatively. An intraclass correlation coefficient was calculated to determine the correlation of the UBM measurement with that performed during surgery. Results: Measurement of the distance of the insertions from the limbus were taken on 79 muscles of the 51 patients: 44 medial rectus (MR) and 35 lateral rectus (LR). Mean age of the patients was 6.4  3.7 years (range, 1-15). A total of 29 children (56.9%) were female. The mean distance of MR from the limbus measured surgically was 5.2  0.6 mm (range, 4-6 mm; median, 5 mm) and measured with the UBM was 5.2  0.9 mm (range, 4-7.6 mm; median, 5.3 mm). Comparable results for the LR muscles were 6.4  0.6 mm (range, 5.5-7.5 mm; median, 6.5 mm) and 6.9  0.7 mm (range, 5.9-8.4 mm; median, 6.9 mm), respectively. An intraclass correlation coefficient of 0.71 signified good agreement between the surgical and UBM measurements of the distance from the limbus of the horizontal rectus muscle insertions. Conclusion: The UBM could be used reliably as a tool before surgery to estimate the distance of the horizontal rectus muscles from the limbus in children with strabismus. (J AAPOS 2002;6:187-90) T he ultrasound biomicroscope (UBM) is a high- frequency (50 MHz) machine (Humphrey Instru- ments, San Leandro, Calif) that depicts the archi- tecture anterior segment structures of the eye in detail, attaining a degree of resolution not possible with the conventional 10 MHz ophthalmic ultrasound. 1 The UBM has been used to image normal eyes, eyes with glaucoma, foreign bodies, tumors, and other disease states of the anterior segment of the eye that fall within its level of penetration of 5 mm. 2-6 It has proven able to define the insertion of extraocular muscles of the eye. 7 Conventional A and B scan ultrasound, 8 computerized tomography, 9 magnetic resonance imaging, 10 and cine magnetic resonance imaging 11 have all been used to define the size and location of the extraocular muscles affected by disease or surgery, but none of these techniques has been able to define the exact insertion of the muscles to the globe and the distance of the insertion from the limbus. The extraocular muscles insert at varying distances from the limbus and standard mean population values are known. 12 Prior strabismus surgery may alter the insertion points of the muscles. A technique that could, before surgery, accurately define the point of insertion of the muscles in relation to the limbus may improve planning for surgical procedures subsequently needed. In this pilot study we used the UBM to calculate the distance of the extraocular muscle insertions in millimeters from the limbus in patients undergoing primary strabis- mus surgery. METHODS A total of 51 patients undergoing primary horizontal stra- bismus surgery at The Hospital for Sick Children, To- ronto, Canada, were recruited for the study. The parents or guardians gave informed written consent, witnessed assent forms were signed when the child was over 7 years old, and the nature and the consequences of the study were explained. Ethical approval was obtained from the hospi- tal’s research ethics board. The research followed the tenets of the Declaration of Helsinki. The inclusion criteria for this study were strabismus cases in children undergoing primary strabismus repair of their horizontal rectus muscles who had normal anterior From the Department of Ophthalmology, The Hospital for Sick Children, Ontario Canada, a University of Toronto, b Department of Population Health Sciences, The Hospital for Sick Children, c and Public Health Services, University of Toronto. d Submitted August 16, 2001. Revision accepted December 14, 2001. Reprint requests: David Smith, MD, Eye Clinic, The Hospital for Sick Children, 555 University Ave, Toronto M5G 1X8, Ontario, Canada. Copyright © 2002 by the American Association for Pediatric Ophthalmology and Strabismus. 1091-8531/2002/$35.00 + 0 75/1/122365 doi:10.1067/mpa.2002.122365 Journal of AAPOS June 2002 187