Retina laser is done by applying a contact lens on the eye. The laser is projected straight on to the retina. Pain occurs only if high power or high intensity burns are produced. If the right amount of laser intensity is used for the right duration, the patient hardly feels pain. 

It is important for the surgeon to adjust the laser settings in such a way as to just produce a light burn on the retina. Harsh burns suggest high power or high intensity burns.