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Editor,—Choristomas are the commonest limbal tumours in children.1 Four types are recognised—dermoid, dermolipoma, single tissue, and complex choristoma. They arise from metaplastic transformation in the mesoblast lying between the optic nerve and the surface ectoderm. Epithelial and dermal, neural, cartilagenous, smooth muscle, lacrimal, sweat, or sebaceous gland tissue may be present.2-4 They are well circumscribed, white or pale yellow, and may be single or multiple, unilateral, or bilateral5 or form a ring.3 Occasionally, epibulbar choristomata are associated with superficial corneal involvement characterised by a vascularised pannus particularly in those containing lacrimal tissue.6
A 7 year old Malaysian Chinese boy was referred to one of us (CL) with cloudy corneas since birth. His vision had always been poor but no strabismus developed. The pregnancy and developmental history were otherwise normal. There was no family history of ocular disease.
Examination revealed 6/18 part vision right and 6/36 left. Bilateral nasal epibulbar dermoids and reticular anterior stromal opacification were noted (Fig 1A).
Neither refraction nor a diagnostic contact lens improved vision. A left 7.5 mm lamellar corneal graft was secured onto a 7.5 mm bed with 16 interrupted, 10-0 nylon sutures. The graft epithelialised over 5 days, under Chloromycetin (chloramphenicol) cover.
The right eye was then patched for 6 hours daily. The sutures were removed at 6 weeks, and his vision improved to 6/18 right (4.00/−5.00 × 20) and 6/18 left (−1.75/−1.25 × 35).
Patching was continued and the patient was discharged to the referring hospital. Histopathology (Fig 1B) showed stromal opacification to a quarter thickness with a large number of vessels in the superficial stroma. The vessels are abnormal having only a single layer of endothelium and little other murine structure.
A 9 week old prematurely born white boy presented with an unsightly lump on his right eye. There were no other congenital abnormalities noted. A maternal uncle had a mass removed from one of his eyes, the nature of which was not known.
Examination revealed a small pale, yellow tumour 3 mm in diameter, on the superonasal limbus of the right eye with an adjacent corneal pannus (Fig 2A). The left eye was normal. Limbal dermoid was diagnosed and excised at 1 year of age. The eye healed well, with a small residual corneal scar. The corneal pannus was not removed and remained static (Fig 2A). Histopathology showed a goblet cell containing stratified, squamous, non-keratinising epithelium, overlying a spindle cell lesion, which embraces islands of adipose tissue and occasional sweat gland elements.
At 18 months the right eye was found to be hypermetropic (+9.50) with associated exotropia (20 prism dioptres) (visual acuity was unobtainable) managed with a contact lens and intermittent patching of the left eye. Aged 3, he had 2/60 vision right, 6/5 left and a 5 dioptre exotropia. Contact lens wear was intermittent and by the age of 3 years, the right eye was +4.00DS with 2/60 vision.
The incidence of corneal vascularisation with epibulbar dermoids is low. It has been reported with ectopic lacrimal tissue choristoma, which may resemble pterygia.7 The majority are unilateral and lie on the temporal cornea. One third are associated with multiple colobomata.8 Henkind et alreported two cousins born of sisters with unrelated husbands, who presented with bilateral corneal choristomata.5 Histology demonstrated a thickened cornea covered by a keratinising stratified squamous epithelium containing hair tufts. Other abnormalities included absence of Bowman's layer and stromal invasion by a dense vascularised collagenous tissue. Penetrating keratoplasty led to early rejection and graft opacification, but in the contralateral eye a lamellar keratoplasty resulted in rapid visual rehabilitation with low astigmatism (as in our case).
Neither of our cases had lacrimal tissue within the biopsies taken indicating that other forms of limbal dermoid may be associated with or possibly induce stromal vascularisation.
Late referral for a specialist opinion occurred with both children. Early referral, especially in unilateral cases, is vital as lamellar keratoplasty and aggressive patching of the fellow eye could prevent amblyopia.
CL is grateful to Mr John Dart for helpful discussions regarding the management of case 1.