Serious corneal causes:
Corneal ulcer (bacterial, viral such as HSV or fungal)
Contact lens-related red eye (acanthamoeba keratitis)
Corneal foreign body: there is often a prior history of wind blowing a foreign body into the eye, or the use of hammering or grinding tools.
Usual symptoms include foreign body sensation, photophobia, blurred vision, discharge, and pain.
Visual acuity and pupil reflexes are usually normal.
On examination, there may be severe conjunctival injection, discharge, eyelid swelling and corneal ulceration demonstrated by fluorescein.