One eye is congested for no reason, which may be related to the entry of foreign objects into the eye, or may be caused by glaucoma or infectious inflammation of the eye. 1. Foreign body in the eye: If the eye accidentally enters a foreign body and fails to remove the foreign body in time, the prolonged friction and stimulation of the foreign body may cause one eye to become bloodshot for no reason. 2. Glaucoma: If one eye suffers from glaucoma, when the acute attack of glaucoma, it can lead to the patient’s intraocular pressure rise, which may cause one eye to be congested for no reason, and may be accompanied by eye itching, eye pain and other symptoms. 3. Ocular infectious inflammation: it is common for one eye to suffer from conjunctivitis, keratitis and other diseases, because of the inflammatory reaction in the eye, under the stimulation of inflammatory products, it can lead to congestion of blood in one eye for no reason, and it can be accompanied by photophobia, tearing and other symptoms. If one eye is congested for no reason, it may be caused by other reasons, which cannot be relieved by resting, or accompanied by eye pain, loss of vision and other discomforts, you should consult a doctor as soon as possible, so as to avoid delaying your condition.