In East Africa, ocular surface squamous neoplasia (OSSN) is a relatively common aggressive disease affecting younger adults. Treatment usually involves surgical excision, however, recurrent disease is quite common (up to 30-66% by 30 months afterwards) and there have been no randomised controlled trials to investigate how to reduce this. For a long time topical 5-fluorouracil (5FU) has been widely used as adjuvant therapy following surgical excision, with many case reports and series in the literature. However, it has not been formally tested in a randomised controlled trial and so we currently do not know if it is effective in preventing recurrent tumours, particularly in the context where more expensive adjuvants or surgical equipment are not readily available. A Cochrane review shows there have been no randomised controlled trials of the various alternatives in clinical practice to investigate how to reduce recurrence.

We propose to conduct a randomised controlled trial to determine whether OSSN recurrence can be reduced by adjuvant topical 5FU chemotherapy following excision. One month after surgical excision of histopathologically confirmed OSSN when the operation site has healed, participants will be randomised to either 5FU eyedrops, or placebo drops to be taken four times a day for 1 month. Patients will be followed for one year to assess the effect. The primary outcome measure is histopathologically confirmed recurrent OSSN.