Redness can occur on the surface of the eye, on the conjunctiva, on the lid margins, on the eye lids, and even on the delicate skin around the eyes. Redness is a very common symptom of Dry Eye, and is frequently diagnosed as ocular rosacea or blepharitis. Redness is an indication of inflammation.

Insufficient, poor quality meibum, or aqueous deficiency can cause redness. Infections can cause redness. Epiphora, tears that overflow, can cause redness. Inflamed conjunctival tissue on the inner side of the eye lids may be red due to infection, allergies to elements in the environment, or allergies to topical OTC and prescription drops and ointments. Saponification, tear film that is frothy, causes redness.

Using saline solution to irrigate the eyes frequently, instead of lubricating drops, can cause redness because the saline does not have proteins and components that lubricate.

Staring when performing activities such as reading, driving, or looking at a computer screen, can cause redness because reduced blinking leads to reduced secretion of meibum, and because the lubrication that takes place during blinking is less frequent. Less frequent blinking also can expose the surface of the eye when the oily layer of the tear film breaks up, permitting evaporation.

Delayed tear clearance can cause redness because stagnant tears contain higher levels of various irritants and toxins.

Eye trauma can also cause redness.