Orbicularis oculi is a broad, flat, elliptical muscle which surrounds the circumference of the orbit and has three functionally distinct parts. The orbital part of this muscle arises from the nasal part of the frontal bone, the frontal process of the maxilla and the medial palpebral ligament between them.1 The orbital orbicularis then spreads above on the forehead, laterally on the temple and below on the cheek, overlapping parts of frontal and zygomatic bones, anterior temporal fascia as well as elevators of upper lip and nostril.2 Its fibers form complete ellipses without interruption on the lateral side, where there is no bony attachment.1
During routine dissection of a cadaver of an adult male of Indian origin (approximate age: 25-35 years), with no obvious congenital abnormalities or marks indicating surgical intervention, the right orbicularis oculi muscle was found to have a lateral bony attachment.
The orbital part of the muscle was found to have a typical origin from the frontal process of maxilla, the nasal part of frontal bone and the medial palpebral ligament. However, the fibers instead of making concentric loops and sweeping upwards and laterally, were attached to the supero-lateral aspect of the body of zygomatic bone (Figure 1). The inferior part of the fascicle of orbicularis oculi had a less defined upper bundle and a well-defined lower bundle of fibers. The upper less defined bundle was found to pass imperceptibly in a concentric manner and then become fibrotic in nature. The lower well-defined bundle passed almost horizontally lateral and then attached onto the supero-lateral aspect of the zygomatic bone (paper slip has been placed under it, as shown in (Figures 1 and 2). The orbital part of the left orbicularis oculi muscle had the typical concentric arrangement of fibers with no lateral attachment. The zygomaticus major and minor muscles of both sides were seen at their normal position.
Orbicularis oculi develops from mesenchyme in the second pharyngeal or hyoid arch.3 The musculature of pharyngeal arches is derived from the paraxial mesoderm of somitomeres and occipital somites. In the second arch, paraxial mesoderm from the sixth cranial somitomere gives rise to muscles of face including orbicularis oculi.4 Their differentiation begins at the 10-12 mm stage of the embryo. Cells from the second arch begin to grow backwards and upward and spread over the first pharyngeal (mandibular) arch, just under the dermis. This process of differentiation lasts till the 16th week although minor modifications occur later.5 It may be theorised that during this stage of differentiation a few fibers of orbicularis oculi get displaced and obtain a bony attachment on the zygomatic bone laterally. The myoblast cells are derived from an adjacent somitomere and their fate is not determined. Therefore, a probable cause of the aberrant muscle is the abnormal migration of the myoblast cells deviating from their predestined fate.
The attachment of the muscle fascicles of orbicularis oculi at a variant site may cause wrinkling of the skin at an abnormal site. It is well documented that the characteristic folding of the skin overlying the contracting orbicularis oculi, leads to permanent wrinkles radiating from the lateral angle of the eyelids in the middle decades of life - the so-called 'crow's feet'.2
Naugle and co-workers6 have demonstrated the value of mobilisation of orbicularis oculi muscle in periocular reconstruction. Yen et al7 predict future applications for the orbicularis oculi muscle graft in facial aesthetics, particularly as useful adjuncts to replace the volume deficit deformity created by protractor myectomy in patients with essential blepharospasm . During any such procedure, the orbicularis oculi which normally has bony attachment only on the medial side, can usually be lifted clean off the zygomatic bone on the lateral side as required. Knowledge of the described variant lateral attachment may thus be of practical use to the plastic surgeon during cosmetic facial surgery.
1. Salmons SWilliams PL, Bannister LH, Berry MM, Collins P, Dyson M, Dussek JE, et al Muscle Gray's Anatomy.38th edition Edinburgh ELBS with Churchill Livingstone:737–900
2. Bron AJ, Tripathi RC, Tripathi BJBron AJ, Tripathi RC, Tripathi BJ. The ocular appendages: eyelids, conjunctiva and lacrimal apparatus Wolff's Anatomy of the Eye and Orbit. 19978th edition London Chapman and Hall Medical:30–84
3. Moore KL, Persaud TVNMoore KL, Persaud TVN. The Eye and Ear The Developing Human: Clinically Oriented Embryology. 19986th edition Philadelphia WB Saunders Company:491–512
4. Larsen WJLarsen WJ, Sherman LS, Potter SS, Scott WJ. Development of the head, the neck, the eyes and the ears Human Embryology. 20013rd edition Philadelphia Churchill Livingstone:351–417
5. Mann I The development of the human eye. 1950 New York Grune & Stratton
6. Naugle TC, Levine MR, Carrol GS. Free graft enhancement using orbicularis muscle mobilization Ophthalmology. 1995;102:493–500
7. Yen MT, Anderson RL, Small RG. Orbicularis oculi muscle graft augmentation after protractor myectomy in blepharospasm Ophthal Plast Reconstr Surg. 2003;19:287–96