This is commonly called “pink-eye” (as if the name of a disease), although that simply means the eye looks red, which everyone already knows / sees, & therefore it doesn’t mean anything. But the most common reason the eye turns red (or “pink”) is because of a virus. There are lots of viruses that can do this (see Differences Among Germs).
The conjunctiva is the outermost covering of the eyeball, and also lines the eyelids (see Diagram — Anatomy of the Eye). Viruses that infect it eventually go away on their own without causing any damage; it’s not dangerous in any way. And nothing cures a virus [sorry].
But Conjunctivitis may be contagious, & freaks people out. Viral conjunctivitis is just like a cold in the eye, but nobody gets all worked up about a runny nose (so if you don’t skip school or work for a cold, you shouldn’t for this either). Medical providers often prescribe antibiotic eye drops, which are completely useless for viruses. They only serve to sometimes cause allergies, & maybe antibiotic resistance (then the drug won’t work when really needed). But if we give an antibiotic, schools & work-places let the person back.
We diagnose Viral Conjunctivitis by seeing one, or usually two, red eyes, which may itch or feel gritty, but do not hurt (true pain suggests more serious illnesses). There’s usually lots of clear tearing; yellow gunk may pile up in the morning from overnight, but is rarely present during the day. The vision is normal (except it may feel blurry now & then due to tears, but certainly not blurry all the time).
Viral Conjunctivitis only lasts a few weeks at the most. If symptoms have been lasting longer, or if a patient has frequent episodes throughout the year, or if they also have lots of sneezing, they likely have allergies (see Allergic Conjunctivitis [airborne]).
Different over-the-counter drops can relieve itching; one is ketotifen (generic name). But ask a pharmacist for help, & say you don’t want a “vasoconstrictor.” Those get rid of redness, but do so by cutting off circulation, which isn’t healthy at all (certainly not if there’s an infection). And don’t buy artificial tears, which are no more useful than tap water.
I often prescribe ketotifen. So if the patient goes back to school or work, they can say they’re on treatment, which will make others happy. The patient obviously needs to practice careful hygiene & wash their hands, as much as possible. We should write a note saying “safe to return, receiving treatment, allow frequent hand-washing” (no need to specify the treatment).