Downloaded from http://bjo.bmj.com/ on February 18, 2016 - Published by group.bmj.com Clinical science Location of the inferior oblique muscle origin with reference to the lacrimal caruncle and its significance in oculofacial surgery Hyun Jin Shin,1 Kang-Jae Shin,2 Shin-Hyo Lee,2 Ki-Seok Koh,2 Wu-Chul Song,2 Young-Chun Gil2 – 1Department of ABSTRACT oblique muscle.11 13 However, these deep bony Ophthalmology, Konkuk Purpose To identify the location of the inferior oblique landmarks are not readily accessible in living sub- University Medical Center, fi Konkuk University School of muscle (IOM) origin with reference to the lacrimal jects and they are not always identi able during Medicine, Seoul, Republic of caruncle in order to facilitate safer oculofacial surgery by surgery. Therefore, an easily accessible external Korea preventing morbidity associated with IOM injury. landmark is required as a reference point. The alae 2 Department of Anatomy, Methods Thirty-seven intact orbits of 20 embalmed of the nose was once used as a reference point for Research Institute of Medical Asian cadavers were dissected. The location of the the IOM origin, but it has high individual variabil- Science, Konkuk University 14–16 School of Medicine, Seoul, medial border of the IOM origin was determined with ity according to the gender and race. Republic of Korea respect to the apex of the lacrimal caruncle. In addition, We have previously reported the usefulness of the size of the IOM origin and the anteroposterior the lacrimal caruncle as an external landmark for Correspondence to distance from the inferior orbital rim to the anterior predicting the location of the trochlea of the super- Young-Chun Gil, Department 17 of Anatomy, Konkuk University border of the IOM origin were measured. ior oblique muscle. The lacrimal caruncle can be School of Medicine, 120 Results The IOM origin was located at a mean used as a reliable external landmark because of its Neungdong-ro, Gwangjin-gu, distance of 1.2 mm lateral and 11.2 mm inferior to the static and less anatomically variable characteristics. Seoul 143-701, apex of the lacrimal caruncle. In half of the orbits, the The purpose of the present study was to determine Republic of Korea; IOM origin was situated just on the vertical line through through cadaveric dissection whether the lacrimal [email protected] the apex of the lacrimal caruncle. The mean length and caruncle can serve as a reliable external landmark Received 5 March 2015 width of the IOM origin were 4.3 and 2.7 mm, for identification of the underlying IOM origin. In Revised 18 May 2015 respectively. The mean anteroposterior distance from the addition, the location of the IOM origin with refer- Accepted 9 June 2015 inferior orbital rim to the IOM origin was 1.9 mm. ence to the lacrimal caruncle, including other alter- Published Online First fi 25 June 2015 Conclusions The lacrimal caruncle is easily identi able native bony landmarks, was investigated. and a reliable external landmark for prediction of the IOM origin. The IOM origin is located approximately MATERIALS AND METHODS where the vertical line through the apex of the lacrimal Thirty-seven intact orbits of 20 embalmed adult caruncle intersects the inferior orbital rim. The findings Asian cadavers (30 male orbits and 7 female orbits; of this anatomical study of the exact location of the IOM 18 right orbits and 19 left orbits), aged 41–96 years origin can help to improve the safety of oculofacial at death (mean, 75.7 years), were dissected. None surgery. of the cadaveric specimens had eyelid or orbital abnormalities. Three orbits that had been disrupted anatomically by previous dissection were excluded. INTRODUCTION This study was performed in accordance with the The inferior oblique muscle (IOM) is a thin, principles outlined in the Declaration of Helsinki. narrow muscle that is responsible for extorsion, ele- Appropriate consent and approval were obtained vation and abduction of the eye. It is the only before using the specimens. extraocular muscle that arises from the anterior The lacrimal caruncle, which is a small, pink, margin of the orbital floor, instead of common ten- triangle-shaped bump in the medial corner of the dinous ring.12Because of this characteristic loca- palpebral fissure, was used as an external landmark tion of its origin, IOM injury has been reported to predict the location of the IOM origin. The – during lower eyelid blepharoplasty,3 5 surgical zygomaticomaxillary suture and the lacrimal tuber- approaches to the orbital floor or the medial cle, which is a small bump on the frontal process of orbit,67and following local anaesthesia for cataract the maxilla situated at the junction between the surgery.89Injury to the IOM is an infrequent lower orbital margin and the anterior lacrimal occurrence, but it can potentially result in devastat- crest, were used as alternative bony landmarks. ing complications such as diplopia, abnormal head posture and ocular motility disturbances.10 Measurements Therefore, understanding the detailed anatomy of The medial canthal area and anterior orbital floor the IOM origin is very important to facilitate pro- were carefully dissected in a layer-by-layer fashion cedural approaches and to avoid complications to evaluate anatomical landmarks. Anatomic dissec- during oculofacial surgery. tion was performed by transcutaneous approach. To cite: Shin HJ, Shin K-J, The location of the IOM origin has been deter- The skin, orbicularis oculi muscle, orbital septum, Lee S-H, et al. Br J mined previously using several reference points, orbital fat and soft tissue surrounding IOM were Ophthalmol 2016;100:179– such as the lacrimal fossa, infraorbital foramen, sequentially removed. Then the IOM carefully sepa- 183. supraorbital notch and trochlea of the superior rated from the capsulopalpebral fascia. Great care Shin HJ, et al. Br J Ophthalmol 2016;100:179–183. doi:10.1136/bjophthalmol-2015-306849 179 Downloaded from http://bjo.bmj.com/ on February 18, 2016 - Published by group.bmj.com Clinical science Figure 1 (A) Cadaveric dissection demonstrating the location of the lacrimal caruncle (asterisk), inferior oblique muscle (IOM), zygomaticomaxillary suture (arrows), medial canthal ligament (MCL) and facial midline (ML). The vertical solid and dot lines indicate reference line through the nasion and the apex of lacrimal caruncle, which was defined as the most superior aspect of triangle-shaped bump, respectively. (B) Photograph taken from the superoanterior direction. The IOM origin relative to the inferior orbital rim (horizontal dot-dash line), lacrimal tubercle (arrowhead) and zygomaticomaxillary suture (arrows). was taken not to disturb the IOM and its origin. Also, medial figure 2). The variability of the location of the lacrimal caruncle canthal ligament (MCL), zygomaticomaxillary suture and with age was assessed by dividing the cadavers into the follow- lacrimal tubercle were identified by palpation and dissection ing three age groups: 40–64, 65–79 and ≥80 years. (figure 1). The topographical relationship of IOM origin to the surrounding structures, as well as the lacrimal caruncle, was iden- Statistical analysis tified. Apex of the lacrimal caruncle was defined as the most The calculations and statistical analyses were performed using superior aspect of triangle-shaped bump. The following para- standard computer software (V.18.0, SPSS for Windows, SPSS, meters (referred to below as #1–#10) were measured: Chicago, Illinois, USA). The gender and side-related differences 1. distance from the facial midline, defined as a sagittal line in each variable were analysed statistically using the running through the nasion, to the apex of the lacrimal independent-samples t test and paired t test, respectively. The caruncle; variability in the location of the lacrimal caruncle (#1, #2 and 2. distance from the bony origin of the MCL to the apex of #3) among the age groups was compared using analysis of vari- the lacrimal caruncle; ance. The threshold for statistical significance was set at 3. length of the MCL; p<0.05. 4. horizontal distance from the apex of the lacrimal caruncle to the medial border of the IOM origin; 5. vertical distance from the apex of the lacrimal caruncle to RESULTS the medial border of the IOM origin; All of the measured values are listed in table 1. None of the 6. horizontal distance from the zygomaticomaxillary suture to measurements differed significantly between the left and right the lateral border of the IOM origin; sides, and the only gender-related difference was in the distance 7. horizontal distance from the lacrimal tubercle to the medial from the inferior orbital rim to the IOM origin (#8) (p<0.05). border of the IOM origin; The measurements of #1, #2 and #3 did not differ significantly 8. distance from the inferior orbital rim to the anterior border among the three age groups (p>0.05). of the IOM origin; The IOM origin exhibited a trapezoid shape. The length (#9) 9. length of the IOM origin; and width (#10) of the IOM origin were 4.3 and 2.7 mm, 10. width of the IOM origin. respectively. The parameters related to the location of the IOM origin from the lacrimal caruncle, the horizontal (#4) and verti- All parameters were measured directly on the cadavers using cal (#5) distances, had mean values of 1.2 and 11.2 mm, digital callipers (CD-15CPX, Mitutoyo, Kanagawa, Japan; respectively. Figure 2 Illustrations of the measured parameters. Detailed descriptions of each of the numbered measurements are given in the text (measurements section in the ‘Materials and methods’ section). (A) Anteroposterior view and (B) superoanterior view. IOM, inferior oblique muscle; MCL, medial canthal ligament; ML, facial midline. 180 Shin HJ, et al. Br J Ophthalmol 2016;100:179–183. doi:10.1136/bjophthalmol-2015-306849 Downloaded from http://bjo.bmj.com/ on February 18, 2016 - Published by group.bmj.com Clinical science Table 1 Measurement items Table 2 Positional relationship between the IOM origin and Anatomic variables Measurement no.