A health camp is conducted in a government school. A 10 year old boy was discovered to have a peculiar lesion in his left eye. Visual acuity in the left eye is 10/20. He also says that he is unable to see clearly at and after dusk.

What is the appropriate treatment? Source : Giulio Ferrari, M.D., and Maurizia Viganó, M.D. N Engl J Med 2013.