Apply drops of sterile saline on the eye.
When a patient presents with a low GCS, you want to perform rapid neurologic exam. I've been seeing our neurologists do a quick simple test for corneal reflexes. Grab a pre-filled sterile saline syringe, typically used to flush IV's, and squirt a few drops on the eye. Look for the patient to blink.
This seems much safer and definitive of a test of the corneal reflex.