The causes of blood in the eyes are as follows: 1, inflammation, conjunctivitis, keratitis, iritis, sclerenitis can show eye congestion, blood in the eyes. 2, dry eye, dry eye symptoms are eye fatigue, foreign body sensation, dryness, signs have bulbar conjunctival vasodilatation, congestion, will show blood in the eyes. 3, visual fatigue, refractive error and not wearing the right glasses, after excessive regulation will show red blood in the eyes. 4, glaucoma, glaucoma is a disease of optic nerve damage due to pathological eye pressure increase, glaucoma acute attack will be eye congestion, eye pain, sudden loss of vision, etc.