Location of the inferior oblique muscle origin with reference to the lacrimal caruncle and its significance in oculofacial surgery

Purpose To identify the location of the inferior oblique muscle (IOM) origin with reference to the lacrimal caruncle in order to facilitate safer oculofacial surgery by preventing morbidity associated with IOM injury. Methods Thirty-seven intact orbits of 20 embalmed Asian cadavers were dissected. The location of the medial border of the IOM origin was determined with respect to the apex of the lacrimal caruncle. In addition, the size of the IOM origin and the anteroposterior distance from the inferior orbital rim to the anterior border of the IOM origin were measured. Results The IOM origin was located at a mean distance of 1.2 mm lateral and 11.2 mm inferior to the apex of the lacrimal caruncle. In half of the orbits, the IOM origin was situated just on the vertical line through the apex of the lacrimal caruncle. The mean length and width of the IOM origin were 4.3 and 2.7 mm, respectively. The mean anteroposterior distance from the inferior orbital rim to the IOM origin was 1.9 mm. Conclusions The lacrimal caruncle is easily identifiable and a reliable external landmark for prediction of the IOM origin. The IOM origin is located approximately where the vertical line through the apex of the lacrimal caruncle intersects the inferior orbital rim. The findings of this anatomical study of the exact location of the IOM origin can help to improve the safety of oculofacial surgery.