Epiphora, or tearing, can occur in one or both eyes, and can have multiple causes. According to the West Boca Eye and Cosmetic Center, the main causes of tearing are the production of too many tears due to irritation, infection or a blockage of the tear drainage system. These conditions typically affect both eyes, but some conditions can cause tearing in only one eye at a time.
Tear Duct Blockage
The tear drainage system in some children may not be fully developed at birth, so these children may have tearing in the one eye when the tear duct is blocked. Typically, the tear duct system opens up by the time the child is a year old, according to the KidsHealth website; if it has not, the child may need a surgical procedure. Adults may develop a blockage of a tear duct in one eye because of sinus problems, injury around the eye or tumor growth, according to the CIGNA website.
Eye Infection
Eye infections may cause epiphora in one eye as well. The eye infection conjunctivitis, which may be caused by either a virus or bacteria, may cause tearing in one eye, according to EyeDoctorGuide.com. Bacterial conjunctivitis usually occurs in both eyes, but can occur in only one, while viral conjunctivitis typically occurs only in one eye.
Glaucoma
Childhood glaucoma can cause epiphora in one eye. In children, glaucoma is usually caused by the incomplete development of the eye, according to the Glaucoma Research Foundation; the drainage angle of the eye may be incomplete or blocked. These patients are very sensitive to light, which can contribute to the watering of the eye.
Bell's Palsy
Bell's palsy is caused by damage to a facial nerve known as the seventh cranial nerve, notes the National Institute of Neurological Disorders and Stroke; this is often a temporary condition, and occurs in one eye. This can cause a weakness of the muscles on one side of the face, as well as drooling, droopy eyelids and excessive tearing in the affected eye.
Corneal Abrasion
A scratch or foreign body in the eye may cause epiphora in one eye. During a corneal abrasion, the outer layer of the cornea comes off and causes tearing, pain and redness. The cornea has the most nerve endings in the entire body, according to Omni Eye Services; these types of injuries are extremely painful. Corneal abrasions typically heal within a few days.
