There are many causes of pain in a particular side of the eye, and it is necessary to help determine whether the eye pain is accompanied by other symptoms and the nature of the pain.
If it is eyestrain or dry eye, the eye pain may also be accompanied by symptoms such as dryness and photophobia.
if it is an inflammatory disease such as conjunctivitis or keratitis, it is usually accompanied by symptoms such as increased discharge, dryness and tearing.
systemic diseases may also cause eye pain, usually accompanied by other systemic symptoms.
For example, herpes zoster eye disease may also cause pain in one eye, but is mostly accompanied by symptoms such as headache on the same side, orbital pain, pain in the temples, and herpes of the skin on the face.