Red flags The following findings are of particular concern: Sudden, severe pain and vomiting Zoster rash Decreased visual acuity Corneal crater Branching, dendritic corneal lesion Ocular pressure > 40 mm Hg Failure to blanch with phenylephrine eye drop Interpretation of findings Conjunctival disorders and episcleritis are differentiated from other causes of red eye by the absence of pain, photophobia, and corneal staining.