Dermoids are choristomas (histologically normal tissue in an abnormal location) and are thought to represent arrest or inclusions of epidermal and connective tissues (surface ectoderm and neural crest cells). They may be associated with abnormal closure of the optic fissure. This collection of epidermal and connective tissue can occur at the limbus (limbal dermoid), in the conjunctiva (dermolipoma), and subcutaneously in and around the orbit. The most common location of subcutaneous periorbital dermoid cysts is the superotemporal and superonasal quadrants of the orbital rim. These dermoids are usually found attached to bone, associated with a cranial suture.
Limbal dermoids are similar to subcutaneous dermoid cysts and consist of epidermal tissue and, frequently, hair (Fig. 1-25). Corneal astigmatism is common in patients with limbal dermoids. Astigmatisms greater than +1.50 are usually associated with meridional and anisometropic amblyopia. Removal of limbal dermoids is often indicated for functional and cosmetic reasons, but the patient should be warned that a secondary scar can recur over this area. Limbal dermoids can involve deep corneal stroma, so the surgeon must take care to avoid perforation into the anterior chamber.
Dermolipomas (lipodermoids) are usually located in the lateral canthal area and consist of fatty fibrous tissue (Fig. 1-26). They are almost never a functional or cosmetic problem and are best left alone. If removal is necessary, only a limited dissection should be performed to avoid symblepharon and scarring of the lateral rectus. Unfortunately, restrictive strabismus with limited adduction frequently occurs after removal of temporal dermolipomas.
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