Redness inside the eyes is considered to be caused by the dilation of the conjunctival blood vessels on the surface of the eyes. Because the surface of the eye is directly exposed to the outside world, it is susceptible to a variety of external stimuli, as well as the influence of pathogenic bacteria appear eye congestion. Because of the lack of rest, the eyes appear visual fatigue, dry eye syndrome, may appear double red blood line increase. If there is a sudden increase in redness in the eyes accompanied by an increase in discharge of varying degrees, the initial consideration is conjunctivitis, which may be related to bacteria, viruses, or fungi. If a foreign body gets into the eye or trauma causes damage to the conjunctiva and cornea, the nerve endings on the surface of the eye are usually stimulated and the eye becomes red, swollen and painful. If there is an increase in redness near the periphery of the black eye, consider that it may be caused by keratitis or uveitis.