The differential for eye pain is quite broad. Unlike other symptoms, here is where you need to take a good history. But never forget to rule out the obvious.
How to Talk to a Patient with Eye Pain
DOCTOR: What seems to be the trouble? You look to be in awful distress.
PATIENT: Yes, doctor. My eyes! They ache, they burn, I can't stand the pain.
DOCTOR (after brief pause): Were you staring directly into the sun again?
PATIENT (after longer, awkward pause): Yes...
DOCTOR (disappointed): And what did we talk about last time?
PATIENT (head hung in equal disappointment): Don't stare directly into the sun.