Ocular surface squamous neoplasia - Review of etio-pathogenesis and an update on clinico-pathological diagnosis.

Ocular surface squamous neoplasia (OSSN) has a varied clinical presentation, the diagnosis of which rests on the histopathological examination of the excised lesion. The term OSSN includes mild dysplasia on one end of the spectrum and invasive squamous cell carcinoma on the other end. This lesion has a multi factorial aetiology with interplay of several factors like exposure to ultraviolet radiation, various chemical carcinogens and viral infections, however role of individual agents is not well understood. With the upsurge of infection with human immunodeficiency virus, a changing trend is seen in the clinical presentation and prognosis of patients of OSSN even in developed countries. Anterior segment optical coherence tomography (OCT) and confocal microscopy, hold promise in in-vivo differentiation of intraepithelial neoplasia from invasive squamous cell carcinoma. Variants of squamous cell carcinoma like Mucoepidermoid carcinoma, spindle cell carcinoma and OSSN associated with HIV infection should be suspected in a case of aggressive clinical presentation of OSSN or with massive and recurrent tumours. Surgery, chemotherapy and immunotherapy are the various treatment modalities which in combination show promising results in aggressive, recurrent and larger tumours.