The symptoms of red and painful eyes are usually due to the following reasons: 1. It is caused by iridocyclitis, an autoimmune disease in which patients usually suffer from rheumatoid arthritis, ankylosing spondylitis and other underlying diseases, and the body’s immune system mistakenly attacks normal tissues such as the red membrane and conjunctiva inside the eye as if they were harmful tissues, resulting in inflammation, which is mainly manifested by The main manifestations are obvious congestion, redness and severe pain in the eye, accompanied by loss of vision and photophobia. 2. is caused by keratitis, when there is inflammation of the cornea, it will cause irritated conjunctival congestion, and at the same time cause corneal sensory nerve fiber hypersensitivity, triggering eye pain. 3. is caused by glaucoma, glaucoma patients will have elevated intraocular pressure, high intraocular pressure will cause the wall of the eye to be stretched, thus causing severe eye pain This can also cause reactive conjunctival congestion.