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. Mean SD lacrimal caruncle Horizontal location of IOM origin Location of caruncle From facial midline 1 19.3 1.8 Lateral to On the vertical line Medial to caruncle through caruncle caruncle From bony origin of MCL 2 13.3 1.9 Length of MCL 3 9.0 1.5 Number 16 19 2 IOM origin from the caruncle % 43.2 51.4 5.4 Horizontal 4 1.2 2.1 Mean (mm) 3.1 0 −3.0 * Vertical 5 11.2 1.4 Overall (mm) 1.2 IOM origin from bony landmark *Negative value of the horizontal distance was defined as a variable located medial Zygomaticomaxillary suture 6 5.9 2.9 to the lacrimal caruncle. Lacrimal tubercle 7 5.0 1.2 IOM, inferior oblique muscle. Inferior orbital rim* 8 1.9 0.7 IOM origin Length 9 4.3 0.8 lacrimal caruncle intersects the inferior orbital rim. Interestingly, Width 10 2.7 0.6 despite inter-individual differences, because the breadth of the Detailed descriptions according to numbers are given in the text (measurement fingernail is slightly more than 1 cm, it could also be considered section in the ‘Materials and methods’ section) and in figure 2. that the IOM origin is located immediately inferior and within a *Statistically significant between both genders. fi fi IOM, inferior oblique muscle; MCL, medial canthal ligament. ngernail breadth from the lacrimal caruncle ( gure 5, right). We have reported previously on the location of the trochlea of the superior oblique muscle with reference to the lacrimal The mean horizontal distance from the facial midline to the caruncle. Trochlea is attached to the anteromedial orbital roof. IOM origin (the sum of #1 and #4) did not differ significantly The tendon of the superior oblique muscle passes through the between male and female cadavers (21.0 and 20.7 mm, inside of the trochlea, which redirects it, thus becoming the p>0.05). functional origin of the superior oblique muscle for movement. Figure 3 demonstrates the positional relationship between the The superolateral tip of the trochlea was located at mean dis- IOM origin and the lacrimal caruncle. In approximately half of tances of 1.6 mm lateral and 15.8 mm superior to the apex of the orbits (51.4%), the medial border of the IOM origin was the lacrimal caruncle.17 In the present study, the IOM origin located on the vertical line through the apex of the lacrimal car- was located at a mean of 1.2 mm lateral to the apex of the lacri- uncle, while it was located lateral to the lacrimal caruncle in mal caruncle. The horizontal distance of 1–2 mm is quite small 43.2% and medial to the lacrimal caruncle in 5.4%. There were and it does not allow the surgeon to discriminate the distance no sex-related, side-related or age-related differences among the by palpation with the fingertips in clinical situations. Therefore, three groups (p>0.05; table 2). the findings presented herein suggest that the lacrimal caruncle, trochlea and IOM origin can be regarded as being located in the DISCUSSION same sagittal plane, and that the lacrimal caruncle could be used The results of the present study indicate that the medial border as a reliable landmark for identification of both the IOM origin of the IOM origin was located at mean distances of 1.2 mm and trochlea (figure 5, left). lateral and 11.2 mm inferior to the apex of the lacrimal caruncle Various landmarks have previously been suggested for identi- – (figure 4). The horizontal distance of 1.2 mm is quite small and fying the location of the IOM origin.11 13 Although bony land- does not allow the surgeon to discriminate the distance by pal- marks such as the supraorbital notch, trochlea and infraorbital pation with the fingertips in typical clinical situations. In add- foramen are static structures and are less influenced by traction, ition, in half of the orbits, the IOM origin was located on the they are rarely used in clinical situations due to the following vertical line through the apex of the lacrimal caruncle (table 2). limitations. With respect to the supraorbital notch, it cannot be Therefore, the IOM origin could be regarded as being located palpated without dissection if it is present in the form of a approximately where the vertical line through the apex of the supraorbital foramen rather than a notch, and in some cases

Figure 3 Illustrations of the positional relationship between the inferior oblique muscle (IOM) origin and the lacrimal caruncle. The IOM origin was located lateral to the lacrimal caruncle (A), on the vertical line through the lacrimal caruncle (B), and medial to the lacrimal caruncle (C). In approximately half of the cases (51.4%), the IOM origin was located on the vertical line through the lacrimal caruncle. MCL, medial canthal ligament.

Shin HJ, et al. Br J Ophthalmol 2016;100:179–183. doi:10.1136/bjophthalmol-2015-306849 181 Downloaded from http://bjo.bmj.com/ on February 18, 2016 - Published by group.bmj.com Clinical science

nose, the location of the lacrimal caruncle did not differ with gender or age group in the present study. The lacrimal caruncle, in contrast to the bony landmarks, allows for easy identification and does not require complex dissection. Furthermore, it is mechanically supported by the MCL and is thus static and less prone to anatomical variations;16 17 21 for example, this ana- tomical structure maintained its original position despite the presence of eyeball dents caused by tissue variations among the cadavers included in the present study. If the original position of the lacrimal caruncle is changed or cannot be identified due to severe eyelid laceration, tearing of the MCL or the presence of medial canthal lesions such as lacri- mal sac tumours, the oculofacial surgeon may use alternative landmarks to identify the IOM origin. Possible alternatives are the zygomaticomaxillary suture (#6) and the lacrimal tubercle (#7). The medial and lateral borders of the IOM origin were located at a mean of 5.9 mm medial to the zygomaticomaxillary suture and 5.0 mm lateral to the lacrimal tubercle, respectively. Figure 4 Illustration of the main measurement values. IOM, inferior The IOM origin was roughly located midway between the zygo- oblique muscle; MCL, medial canthal ligament; ML, facial midline. maticomaxillary suture and the lacrimal tubercle. Clinically, these anatomical landmarks are located closer than previously (reportedly 5–10%) this structure is entirely absent.18 19 The used bony landmarks such as the supraorbital notch, trochlea trochlea is a structure that is rarely dissected during orbitofacial and infraorbital foramen, and they are more accessible. surgery because of the subsequent associated complications, and Moreover, the zygomaticomaxillary suture line could sometimes the infraorbital foramen is basically an extraorbital structure and be palpated externally without dissection. is somewhat distant from the IOM origin. Several previous studies have investigated the anteroposterior In one previous study, it was suggested that the alae of the distance from the inferior orbital rim to the IOM origin. The nose could be used as external landmarks of the IOM origin.20 cadaveric study performed by Mowlavi et al11 involving orbits Since the alae of the nose are larger in males than in of Caucasians reported a mean distance of 5.14 mm, which is females,14 15 those authors suggested that the IOM origin— greater than that presented herein (1.9 mm) and the range which is located more laterally in males since the skull size is found in another Asian cadaveric study (0.97–3.2 mm).13 20 larger in males than in females—offsets the possible gender dif- This difference in anteroposterior distance may be attributable ference. However, information on gender differences in the to racial differences and differences in the residual soft tissue at IOM origin is currently insufficient. Except the aforementioned the time of measurement. study, no previous study statistically compared the horizontal Limitations of the present study include the use of embalmed location of the IOM origin between the genders. The present cadavers rather than being performed in vivo. Formalin fixation study found that the horizontal location of the IOM origin did typically causes a width reduction of approximately 4% in tissue not differ with gender. Moreover, the position of the nasal alae specimens.22 However, the lacrimal caruncle, which is a dense could be altered by placement of a nasotracheal intubation in fibrous connective tissue that is mechanically supported by the cases requiring general anaesthesia, rendering it an inaccurate MCL, almost maintained its original position irrespective of soft- anatomical landmark for the IOM origin during surgery. tissue alterations such as eyeball dents in the present cadavers. In The lacrimal caruncle appears to be a good landmark for addition, since formalin fixation does not affect the bone size or identification of the IOM origin. Contrary to the alae of the the position of the IOM origin, we believe that the relationship

Figure 5 Illustration demonstrating that the lacrimal caruncle, trochlea and inferior oblique muscle (IOM) origin can be regarded as being located in the same sagittal plane (left). Simple criteria for the positioning of the IOM origin (right). MCL, medial canthal ligament.

182 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 between the lacrimal caruncle and the IOM origin would be 4 Seiff SR. Complication of upper and lower blepharoplasty. Int Ophthalmol Clin similar in the in vivo situation, and is thus directly applicable to 1992;32:66–77. 5 Ghabrial R, Lisman RD, Kane MA, et al. Diplopia following transconjunctival surgical situations. Another limitation is that most of the speci- blepharoplasty. Plast Reconstr Surg 1998;102:1219–25. mens were from elderly individuals, and the anatomical structure 6 Kakizaki H, Nakano T, Asamoto K. Safe limits for the incisional area in a in elderly subjects might differ from that in younger individuals. transcaruncular approach to the medial orbit and ethmoid sinus. Ophthal Plast However, given that the position of the lacrimal caruncle in the Reconstr Surg 2007;23:497–8. present study did not differ significantly among the included age 7 Tiedemann LM, Lefebvre DR, Wan MJ, et al. Iatrogenic inferior oblique palsy: intentional disinsertion during transcaruncular approach to orbital fracture repair. groups, we believe that the results would be applicable to patients J AAPOS 2014;18:511–14. of all ages. The dissections were performed in Asian cadavers, 8 Hunter DG, Lam GC, Guyton DL. Inferior oblique muscle injury from local anesthesia and location of the IOM origin may be different in Caucasian, for cataract surgery. Ophthalmology 1995;102:501–9. African and other ethnicities. Therefore, future studies should 9 Bleik JH, Zaatari GS, Cherfan GM. Inferior oblique muscle injury after peribulbar anesthesia presenting as ipsilateral superior oblique palsy: a clinicopathologic report. investigate racial differences in the IOM origin using the same J AAPOS 1995;10:178–9. landmarks, such as the lacrimal caruncle. 10 Galli M. Diplopia following cosmetic surgery. Orthopt J 2012;62:19–21. In conclusion, we have demonstrated herein that the lacrimal 11 Mowlavi A, Neumeister MW, Wilhelmi BJ. Lower blepharoplasty using bony caruncle can be used as a reliable reference point for identifying anatomical landmarks to identify and avoid injury to the inferior oblique muscle. – the IOM origin because of its static and less anatomically vari- Plast Reconstr Surg 2002;110:1318 22. 12 Yousif NJ, Sonderman P, Dzwierzynski WW, et al. Anatomic consideration in able characteristics. The IOM origin was located at an approxi- transconjunctival blepharoplasty. Plast Reconstr Surg 1995;96:1271–6. mate point where the vertical line through the apex of the 13 Paik DJ, Shin SY. An anatomical study of the inferior oblique muscle: the embalmed lacrimal caruncle intersects the inferior orbital rim. These cadaver vs the fresh cadaver. Am J Ophthalmol 2009;147:544–9. results, when combined with bony landmarks, facilitate predic- 14 Ngeow WC, Aljunid ST. Craniofacial anthropometric norms of Malaysian Indians. Indian J Dent Res 2009;20:313–19. tion of the exact location of the IOM origin and can help 15 Burriss RP, Little AC, Nelson EC. 2D:4D and sexually dimorphic facial characteristics. towards improving the safety of oculofacial surgery. Arch Sex Behav 2007;36:377–84. 16 Farahvash MR, Abianeh SH, Farahvash B, et al. Anatomic variations of midfacial Acknowledgements We are grateful to Kwan-Hyun Youn, PhD, medical illustrator muscles and nasolabial crease: a survey on 52 hemifacial dissections in fresh ([email protected]) for the illustrations. Persian cadavers. Aesthet Surg J 2010;30:17–21. Contributors Planning: HJS, Y-CG. Data collection: K-JS, S-HL, Y-CG. Conduct and 17 Shin HJ, Gil YC, Shin KJ, et al. Identification of the trochlea with reference to the reporting of the work: HJS, Y-CGil, K-SK and W-CS. lacrimal caruncle, and its significance as a landmark in orbitofacial surgery. J Plast Reconstr Aesthet Surg 2015;68:351–5. Competing interests None declared. 18 Wilhelmi BJ, Mowlavi A, Neumeister MW. Upper blepharoplasty with bony Provenance and peer review Not commissioned; externally peer reviewed. anatomical landmarks to avoid injury to trochlea and superior oblique muscle tendon with fat resection. Plast Reconstr Surg 2001;108:2137–40. Data sharing statement No additional data available (technical appendix, 19 Sithiporn A, Thanasilp H, Vilai C. 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Shin HJ, et al. Br J Ophthalmol 2016;100:179–183. doi:10.1136/bjophthalmol-2015-306849 183 Downloaded from http://bjo.bmj.com/ on February 18, 2016 - Published by group.bmj.com

Location of the inferior oblique muscle origin with reference to the lacrimal caruncle and its significance in oculofacial surgery Hyun Jin Shin, Kang-Jae Shin, Shin-Hyo Lee, Ki-Seok Koh, Wu-Chul Song and Young-Chun Gil

Br J Ophthalmol 2016 100: 179-183 originally published online June 25, 2015 doi: 10.1136/bjophthalmol-2015-306849

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