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The outermost covering of the globe is universally labelled as conjunctiva. It is a mucous membrane similar to the mucous membrane elsewhere in the body, containing blood vessels, nerves and lymphatic channels supplying the anterior segment of the eye. Apart from the nutritive function, it also contributes to the formation of tear film through the microscopic goblet cells which produce mucin. Being at the distinctive position of covering the eye ball, it is frequently involved in array of local and systemic disorders. These vary from conjunctivitis and innocuous pingulecula and Bitot spot’s at the one end to precarious Kaposi’s sarcoma and malignant melanoma at the other end. Very often we come across very innocent looking lesions in which we are very sure of the diagnosis relying on our clinical acumen and experience. Our overconfidence is often shattered when the report of histopathology arrives, forcing us to re-think our strategies to manage such patients. With this background we present our distinctive case of conjunctival cyst which extended to the cornea and gave the appearance of a pterygium.1

A seventy five year old man presented to our department  with chief complaints of diminution of vision in left eye for the past one year , associated with redness and watering for the past six months. There was no history of associated pain, itching or burning sensation from the left eye.  No relief was obtained despite prescription of multiple eye drops (details not available) 

On examination distance vision 6/60  right eye, corrected to 6/24. Counting finger counting close to face  left eye. Slit lamp biomicroscopy revealed  nuclear cataract grade II along with cortical cataract was right eye. Left eye revealed multiple epithelial, sub-epithelial and stromal corneal opacities. Nasal pterygium seen in left eye extended to a cystic growth in forniceal conjunctiva. Mass was translucent, oval, about 4 mm in diameter and freely mobile from the underlying structures (Figure1).

Pterygium was excised completely leaving underlying sclera bare and translucent cyst in inferior fornix was excised  (Figure.2). 

Histopathology revealed hyperplastic stratified squamous epithelium with attached sebaceous glands, hair follicles and lacrimal gland suggestive of conjuctival choristoma. (Figure 3)

Tumors of cornea and conjunctiva often present a diagnostic challenge. Tumors of ocular surface are classified according to the cell type they originate from including epithelium, melanocytes, lymphocytes, vascular epithelium and mesenchymal cells. Conjunctiva has squamous cuboidal cells that cover a rich connective tissue composed of delicate substantia propria with abundant blood vessels, lymphatic channels and nerve endings. The lamellar arrangement of the corneal stroma and the condensation of the outer layer into bowman’s layer protect the cornea  from deep invasion by many tumors that arise in conjunctiva.2 A choristoma is a congenital tumor like growth that contains displaced epithelial cells and other dermis like elements not normally indigenous to the site they are found. Four types of choristoma are recognised: Simple, Dermoids, Dermolipoma and complex choristomas. Dermoids are universally defined as normal tissue in abnormal location. It implies that in case of conjunctiva, stratified squamous epithelium along with hair follicles and sweat glands. If however, special tissue elements like those of cartilage or lacrimal glands are present then it is classified under choristomas. The most common episcleral choristoma is dermoid. Conjunctival dermoids are well well circumscribed, smooth, elevated white, round to oval most commonly present at inferotemporal limbus. On HPE keratinized epithelium, hair, sebaceous and sweat glands, smooth muscles, cartilage etc .Complex choristoma shows presence of bone, cartilage, lacrimal gland , hair follicles etc.3 It differs from hamartoma which is an excessive proliferation of normal tissue at the normal site. Choristomas may occur in association with ocular coloboma, Goldenhar syndrome or epidermal nevus syndrome. The differential diagnosis should include chalazion, dermoid, dermolipoma, pyogenic granuloma and papilloma.4 

Conjunctival choristomas in palpebral conjunctiva are very rare growths. Epibulbar choristomas are common in children, 5 with only 15 cases been reported so far. They commonly present as small translucent swelling resembling the retention cyst. Treatment includes surgical excision when symptomatic or causing cosmetic concern. Recurrences or malignant transformation have not been reported.6  Dermoid cyst presenting as a chronically red eye has been documented.7 The fact that our case of choristoma manifested at  older age of seventy- four , and  masquerading  as inflamed pterygium makes it a rare presentation