- Hypertelorism is not a disease but a physical condition in which the orbits are separated by an abnormal distance. This distance is measured radiologically as the distance between the dacryons located at the point of junction of the maxillary bone, lacrimal bone, and frontal bone on the anterio medial wall of the orbit. At birth it is 15 mm and grows to 25 mm in girls by the age of 15 and may grow up to 28 mm in adult males by the age of 18. Widely spaced eyes are a sign of beauty up to a point. Unfortunately and probably incorrectly in most cultures very widely spaced eyes in an individual arouse suspicions of the individuals’ mentation.
- Classically hypertelorism results because of abnormalities in the median part of the neuroectodermal crest resulting in clefts (with or without herniation of intracranial contents) or when this part of the crest is dysplastic causing an abnormal broadening. In either event the normal medial migration of the orbits is stalled. If the clefting is unilateral as when the medial migration of the mesoderm fails to fuse with the central neuroectoderm in the upper part of the skull, a unilateral hypertelorism will result also called dystopia. When the cleft in this area is multi-dimensional the orbit will be translocatedaccordingtothedefect.
- The general description of the operative technique has already been related in the earlier chapter including the separation of the eyeball from its bony shell (see photograph below) leaving the eyeball hanging on the optic nerve.
These are some points specific to the surgical treatment of hypertelorism.
- Hypertelorism is best treated by a combined intra- and sub-cranial approach by a frontal craniotomy.
- In order to move the orbits medially a circumferential osteotomy 360° is required within the orbit. External cuts include all the bones that form the orbit.
- For this purpose sharp oscillating power driven instruments are now commonly used. The osteotomy in the roof, medial and inferior walls should be behind the equator of the eyeball.
- Structures in the medial plane, ethmoids included are reduced proportionate to the excess breadth that they have come to occupy.
- The orbits in their new position need to be effectively and rigidly fixed to each other and to the frontal bar.
- The medial canthal ligaments are brought to their new positions and fixed by a durable suture to each other through the nasal bone.
- Lateral canthal ligaments might be a restraining force against the movement of the eyeball and they too might need to be detached, relocated and fixed.
- Any aesthetic abnormalities caused by the extirpation of the naso-ethmoidal area might need to be corrected by an onlay bone graft which can be harvested from the parietal bone which is already exposed.
- This procedure might need to be performed transcutaneously (externally), if the area is very wide and the overlying skin is in great excess and contains any herniation of intra-cranial contents, these then are reduced and the gap in the dura and the bone is repaired with a suitable material. In this event surgical work on the upper and lower alar cartilages can be also undertaken under vision through this incision.
- The gap left on the lateral side by the movement of the orbits medially can be also filled by a bone graft from the parietal calvarium.
N.B. Hypertelorism caused by a craniostenotic pathology which is treated in early infancy need not be accompanied by surgical treatment of hypertelorism which can follow later.
- Messers Jackson, Munro, Salyer and Whitaker in the year 1982 compiled an atlas of craniofacial surgery with the help of excellent line drawings done by Messers Winn and Barrows.
- This chapter draws heavily from the atlas and that debt is acknowledged. Based on the line drawings in that atlas an actual skull has been used to create diagrams in this chapter. The compiler of these notes also thanks Mukund Jagannathan, Head of the Dept. of Plastic Surgery at the LTMG hospital in Mumbai not only for allowing the use of the skull but for vetting the information in this chapter and also for general guidance. Nitin Mokal who kindly supplied photographs for the previous chapter was also of great help.
Regarding figures 16 and 19: Mukund Jagannathan, Craniofacial surgeon from Mumbai adds:
With the advent of much better implements to effect rigid fixation of bone segments the step of preserving the frontal bar has now been dispensed with and only one craniotomy is performed above the supraorbital ridge. This has one great advantage in that a dystopic orbit can now be de-rotated to place it in the desired location. In the earlier operation the presence of the frontal bar allowed only a medial movement of the orbits because there was little or no space for the arc of de-rotation.