There are many causes of redness and congestion of the eyes, the most common cause is external stimulation, but also may be caused by ocular disease factors, such as conjunctivitis, dacryocystitis, glaucoma and so on. 1. External irritation (1) Visual fatigue: Due to staying up late or reading books and newspapers for a long time, playing cell phones, watching computers, and doing fine work in dim light, the eyes can not get normal rest and visual fatigue occurs, which is manifested as redness and congestion of the eyes. (2) Foreign bodies in the eyes: due to the wind, sand, flying insects and other foreign bodies into the eyes, in the eyes of the friction caused by redness, congestion, pain and so on. (3) Eye trauma: redness, congestion and pain in the eyes due to eye contusion, chemical injury and electric light stimulation injury. 2. Eye diseases (1) Conjunctivitis: Inflammation of blood vessels in the conjunctiva due to bacterial, viral, allergic and other stimuli, manifested as redness, congestion and swelling of the eyes. (2) Dacryocystitis: Narrowing or blockage of the nasolacrimal duct due to various reasons leads to retention of tear fluid in the lacrimal sac, which triggers bacterial infection, resulting in redness, congestion, pain, photophobia, and tearing of the eyes. (3) Glaucoma: Optic nerve atrophy due to pathologically high intraocular pressure, manifested by redness and congestion of the eyes, photophobia, tearing, eye blurring and vision loss. Redness and congestion of the eyes, with no relief of symptoms after rest, should be examined and treated under the guidance of a doctor.