An eye becomes red when the conjunctival vessels are engorged. There are many, many causes of a red eye (not a complete list, only to illustrate)
Infections:
1. globe---conjunctivitis, keratitis, iritis, retinitis
2. Surrounding structures---eyelids, sinuses, nasolacrimal system…
Inflammations:
scleritis, episcleritis, uveitis, iritis, retinitis…
Anatomic:
entropion, ectropion, trichiasis, proptosis, nocturnal lagophthalmos, telangiectasia and hemangiomata of the conjunctival vessels…
Mechanical:
Contact lenses, foreign body
SYMPTOM
1. Itching
2. Scratchiness
3. Burning
4. Localized tenderness
5. Deep, intense pain ***
6. Photophobia ***
7. Halos ***
*** potentially serious symptoms
CAUSE
1. Allergy
2. Foreign body, dry eye
3. Lid, conjunctival, corneal disorders
4. Stye, chalazion
5. Corneal abrasions, iritis, acute glaucoma, sinusitis
6. Corneal abrasions, iritis, acute glaucoma
7. Corneal edema
Red Eye