Researchers today deal a fresh blow to jacket and tie culture - by exposing the potential health hazard from the knots round men's necks.

Tests by eye specialists in New York suggest those who think a tighter tie might make them look smarter could be increasing their risk of glaucoma, a condition which, untreated, can lead to loss of sight.

Men with thick necks and white-collar professionals might also be in greater danger of damaging their vision, according to a study published in the British Journal of Ophthalmology.

The verdict will encourage a sense of well-being in men who prefer an open-necked dress code. But it could spell trouble for those who have tried to make ties fashion accessories rather than statements about their wearers' old school or club.

The researchers tested the internal blood pressure in one eye in each of 20 healthy men and 20 patients with glaucoma. High pressure is an important risk factor in the development and progression of glaucoma, a disease in which the movement of fluid in and out of the eye becomes blocked, threatening damage to the retina and optic nerve.

The tests were conducted three times - when participants wore open collars, three minutes after they donned tightly-knotted ties, and three minutes after loosening them again.

The healthy men were on average younger than those with glaucoma. Pressure in the eye rose in seven in 10 of them after donning tight ties, compared with six in 10 of those who had glaucoma. Yet there were no differences before ties were tightened and loosened.

The study's authors, led by Robert Ritch, of the New York Eye and Ear Infirmary, speculate that a tight tie constricts the jugular vein and raises blood pressure both in the vein and inside the eye.

Wearing ties more loosely should become a habit for those wishing to reduce the risk of glaucoma, they suggest. And men should wear no tie at all when undergoing eye tests.