Epibulbar dermoids are benign congenital tumours that contain choristomatous tissue (choristomas are congenital overgrowth of normal tissue in abnormal locations). Most frequent site for epibulbar dermoid is inferior-temporal part of limbus (junction between cornea and conjunctiva). Occasionally, dermoid may be present entirely within cornea or may be localised to conjunctiva. Choristomas consist of ectodermal and mesodermal tissues in varying proportion and may contain epidermal appendages, skin, sweat gland, connective tissue, muscle, tooth, fat, lacrimal gland, bone, cartilage, vascular or neurologic tissue.
There are three broad categories of dermoids depending upon the location:
Limbal: Limbal dermoid straddles the limbus and is the most common type. Limbal dermoids are superficial usually, but may affect deeper structures as well.
Corneal: This includes dermoid which involves superficial cornea only. This spares the limbus, descemet membrane and endothelium.
Anterior segment: This group includes dermoid which involves the entire anterior segment. Dermoid replaces cornea with a dermolipoma or lipodermoid that may involve iris, ciliary body and the lens.
Lipodermoids consists of adipose tissue with surrounding dermis-like connective tissue. Lipodermoids are soft, yellow, movable subconjunctival masses located commonly at the limbus or outer canthus.
Basak Samar K, Atlas of Clinical Ophthalmology, 2nd ed. Jaypee Brothers Medical Publishers (P) Ltd, 2013, New Delhi, P. 61-63.
Kanski,Jack J. Clinical Ophthalmology, A Systematic Approach .Third Edition.UK. Butterworth Heinemann, 1994. P 206-207.
Epibulbar dermoids are present at birth but may be recognised during first or second decade of life. These appear to enlarge as a person matures.
Dermoids may enlarge slowly, especially at puberty or due to irritation or trauma. Enlarging dermoid may produce amblyopia (lazy eye with lack of development of vision not related to eye health problem) if it produces significant corneal astigmatism (refractive optical defect in which sharp focus is not formed on retina) or it blocks visual axis.
Most of the patients present before the age of 16 years and may have symptoms such as:
- Decreased or poor vision.
- Foreign body sensation in eye.
- Enlarging ocular mass.
- Cosmetic disfigurement.
Most of the cases of epibulbar dermoids are sporadic and no relation is found with any known toxin or irritant.
Several theories are proposed to explain development of epibulbar dermoids:-
- One such theory suggests an early developmental error causing metaplastic transformation of the mesoblast between rim of optic nerve and the surface ectoderm.
- Another mechanism suggests sequestration of pluripotent cells during embryonic development of the surrounding ocular structures.
Epibulbar dermoids are generally not inherited except for few exceptions.
Goldenhar syndrome (oculo-auriculo-vertebral dysplasia): In Goldenhar syndrome, there is familial presentation with multi-factorial pattern of inheritance of limbal dermoids in association with systemic disorders.
Two rare forms of dermoids, annular limbal and corneal dystrophy form present in multiple family members.
Diagnosis of dermoid depends upon the clinical presentation.
Dermoids are dome shaped, fleshy and may have fine superficial blood vessels. Dermoids may appear keratinised and may show hair follicles and cilia.
Dermoid is usually single, unilateral pink-white-grey mass, one to five mm in size. Most of the epibulbar dermoids are present at the inferior-temporal part of the limbus. Clinical picture is highly variable. These may be multiple, bilateral, minutely small or big enough to obscure the cornea.
Rarely, dermoids may be localised to cornea or the bulbar conjunctiva only.
Dermoids may show associated ocular abnormalities such as:-
- Lid coloboma (full-thickness defect of the lid).
- Iris and choroidal coloboma.
- Aniridia (absence of iris).
- Microphthalmia (small eyeball).
- Duane retraction syndrome and other ocular motility disorders.
- Lacrimal duct stenosis.
- Staphyloma (protrusion) of cornea and sclera.
Associated systemic abnormalities may be:
- Goldenhar syndrome: In Goldenhar syndrome, limbal dermoids are associated with pre-auricular appendages and auricular fistulae. Other abnormalities include hemi-facial/ craniofacial microsomia (lower half of one side of face is underdeveloped), microtia (pinna or external ear is poorly developed) and vertebral anomalies (such as fused cervical vertebrae, hemi-vertebrae, spina bifida, lumbosacral anomalies and occipitalisation of first cervical Atlas vertebra). Epibulbar dermoid straddles the limbus in the infero-temporal quadrant. It is bilateral in about 25% of cases. A subconjunctival lipodermoid may be present in supero-temporal quadrant in about 50% of cases. This lipodermoid may blend with epibulbar dermoid.
Facial malformations include macrostomia (unusually wide mouth), micrognathia (small jaw), dental abnormalities and facial asymmetry.
There may be associated systemic abnormalities involving cardiovascular, renal, genitourinary and gastrointestinal systems.
- SCALP syndrome: Acronym SCALP includes rare clinical findings such as Naevus Sebaceous (benign neoplasm occurring mainly on scalp and face), Central nervous system malformations, Aplasia cutis congenita (absence of a portion of skin in a localised or widespread area at birth), Limbal dermoid and Pigmented naevus.
Epibulbar dermoids should be differentiated from:
- Foreign body granuloma.
- Corneal scar due to trauma or infection.
- Atypical pterygium (wing like triangular sheet on bulbar conjunctiva).
- Magnetic Resonance Imaging (MRI): MRI may be useful in distinguishing lesions extending into conjunctival fornix or lateral canthus (junction between lower and upper eyelid) and entangling with orbital fat and extra-ocular muscles.
Epibulbar dermoids have choristomatous tissue which includes epidermal appendages, adipose tissue, lacrimal gland tissue, smooth and striated muscle, nervous tissue, tooth, bone and cartilage. It may also have lymphoid nodules and vascular elements. The surface of dermoids consists of corneal or conjunctival epithelium.
Management should be carried out under medical supervision.
Management may include:
- Lubricating drops and ointments: Lubricating drops and ointments help to prevent foreign body sensation.
- Periodic removal of irritating cilia.
Surgical therapy is the mainstay of treatment and is indicated for:
- Interference with vision.
- Significant cosmetic disfigurement.
Surgery is done only when the risk of subsequent scar formation or other complications is outweighed by the benefits of vision improvement and cosmetic appearance.
Attempts at complete removal of epibulbar dermoid are unnecessary. The lesion may extend into deeper structures of the eye and the risk of perforation increases if attempts are made to remove the lesion completely.
Procedure of choice for removal of epibulbar dermoid is:
- Superficial sclero-keratectomy: In superficial sclero-keratectomy, epibulbar dermoid is removed flushed with the surface of eyeball.
After sclero-keratectomy, exposed area may be covered by:
- Conjunctival flap: The exposed sclera should be covered by relaxing adjacent conjunctiva and sewing it to the defect.
- Lamellar keratoplasty is done to cover deep excision of cornea.
- Amniotic membrane graft: Single or multi-layered amniotic membrane graft may be used to cover large patches of bare sclera. It may be secured by sutures or fibrin glue.