A MAN has been treated in hospital after he appeared to be crying blood - but doctors can't work out what caused it.

The 22-year-old went to hospital after it happened twice, but tests on his eyes revealed they were in working order.

Crying blood, known medically as haemolacria, can be caused by a number of things and can leave a patient crying red-tinged tears or tears made entirely of blood.

Doctors at Andaman and Nicobar Islands Institute of Medical Sciences in India sent the man for blood tests and a liver function test, but both came back normal.

Worried he might have a clotting problem, which can increase the risk of deadly internal bleeding, doctors sent him for more tests.

But they all came back normal, meaning his blood was clotting normally.

Tests for infection and genetic diseases also came back normal.

After a number of tests doctors were unable to conclude the cause of the patients condition, according to the British Medical Journal case report.

They decided his haemolacria was idiopathic, meaning the cause is unknown, which accounts for about 30 per cent of cases.

"Haemolacria is a condition in which the patient has bloody tears, instead of normal watery tears," Dr Robert James wrote in the report.

"It is a symptom of a number of diseases.

"It may be indicative of a tumour in the lacrimal [glands behind the eye] apparatus. Severe bacterial conjunctivitis or local injury to the eye can present with haemolacria.

"In women ectopic endometrial tissue deposition in the lacrimal duct can give rise to bloody tears during the menstruation."

An enlargement if the veins surrounding the eyes or conjunctivitis in the inner lining of the eyelid can also cause bleeding, as can a tumour in the veins surrounding the eyes.

Haemolacria is an incredibly rare condition and although it's usually harmless, you should see a doctor if you notice blood in your eyes.

Most cases usually resolve as quickly as the start.