The self-inflicted removal of one or both eyes, which has traditionally been attributed to sexual guilt, is, in fact, caused by untreated psychotic illness, such as schizophrenia, researchers have revealed.

This type of self-inflicted mutilating injury is fortunately very rare, the researchers noted, but over 50 cases have been published in medical journals over the past 50 years.

The phenomenon, which is variously referred to as oedipism, self enucleation or auto-enucleation, has been linked to sexual guilt - an association that stems from both classical Greek mythology and the Bible.

In Sophocles' tragedy, Oedipus the King (Oedipus Rex), it is prophesised that the protagonist will kill his father and sleep with his mother, and he ends up stabbing himself in both eyes.

This type of incestuous sexual attraction was popularised by the psychoanalyst Sigmund Freud in the 19th century who attributed it to some of his patients, in what he described as the Oedipus complex.

A more persistent belief is that self enucleation is specifically associated with Christian religious guilt, as all the published cases have come from countries that were predominantly Christian, and some patients seem to have been influenced by a passage in the Gospel of Matthew.

This says: "And if thy right eye offend thee, pluck it out, and cast it from thee; for it is profitable for thee that one of thy members should perish, and not that thy whole body should be cast into hell."

But the researchers, who have carried out two systematic reviews of published case reports of self enucleation and major self mutilation, conclude that self enucleation is invariably associated with psychotic illness, particularly untreated schizophrenia.

This is because the cases reported to date have come from a wide range of cultures, including China and Japan, and none described events remotely similar to Oedipus Rex.

And in almost every one, the patients held bizarre delusional beliefs about their eyes and had associated hallucinations, said the researchers.

"We concluded that cultural beliefs are not likely to be the cause of self enucleation because they are shared by a large number of people and cannot be a good explanation for the actions of the tiny minority who self enucleate," they wrote.

"In contrast, the rare and disturbing psychotic symptoms are a more plausible explanation for self enucleation than Oedipal conflicts or religious guilt," they stated.

The sexual guilt theory has persisted for as long as it has because the act of deliberate self blinding is so shocking and hard to comprehend, they suggested.

"Each case is disturbing and it is perhaps not surprising that doctors have sought to explain the patients' behaviour in the secure frameworks of their religious and cultural beliefs," they asserted.

"However, a more helpful way of understanding and responding to self enucleation is to recognise that it is a rare complication of severe psychosis that requires urgent medical attention," they concluded.