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Ocular surface squamous neoplasia: Population demographics, pathogenesis and risk factors

Background: Ocular surface squamous neoplasia (OSSN) is a unifying term used to describe conjunctival intra-epithelial neoplasia, squamous cell carcinoma in situ and invasive squamous cell carcinoma.Aim: The aim of this article was to describe the demographics, clinical features, pathogenesis and risk factors of OSSN.Method: A literature search was conducted using the search criteria ‘ocular surface squamous neoplasia’, ‘diagnosis’, ‘epidemiology’, ‘pathogenesis’ and ‘risk factors’.Results: Ocular surface squamous neoplasia is the most common ocular tumour, with incidence rates ranging from 0.01 to 3.4 per 100 000 persons/year. There are two main patterns  of disease presentation: older white males in temperate climates where human immunodeficiency virus (HIV) and human papilloma virus (HPV) are not associated; and a younger patient population in tropical climates where HIV and HPV are more prevalent. The pathogenesis primarily revolves around ultraviolet B exposure and HPV infection that cause genetic mutations and uncontrolled cellular proliferation, whilst HIV infection and vitamin A impair tumour surveillance mechanisms. Ocular surface squamous neoplasia is first suspected clinically before formal confirmation of the diagnosis. Morphologically, it can be divided into three groups: placoid, nodular and diffuse. Placoid lesions can further be sub-divided into gelatinous, leukoplakic and papilliform lesions. Nodular lesions have the poorest prognosis, with the highest risk of metastasis and recurrence.Conclusion: Ocular surface squamous neoplasia is a common ocular tumour associated with ultraviolet radiation, HPV and HIV infection. The pathogenesis revolves around acquired genetic mutations, unregulated cellular proliferation and impaired tumour surveillance mechanisms.