Is it possible to heal short-sightedness?

Yes, with time, persistance and energy anything can be healed.
Just use basic healing. Engulph whatever it is that needs healing in Gold-White light/energy and affirm that it is being healed of it's ailment. Remember to never take ownership of the illness or problem. Saying "my cancer" will only help to tie the cancer to you stronger.

-En Haradren Amlug.