Wearing your tie too tight could put you at increased risk of blindness, say doctors.
Tying a tight knot could be dangerous, say docs
The small study in New York measured the pressure of the fluid in the eyeball in a small group of men before and after they attached their tie.
They found a significant rise - and warn that long-term pressure rises have been linked to the condition glaucoma.
Glaucoma is diagnosed when increases in pressure are likely to cause damage to the eye, and in its most common form, affects approximately 1% of 50-year-olds in the UK. It is the most common cause of irreversible blindness in the world.
Researchers from the New York Eye and Ear Infirmary in New York tested 40 men, half of whom were healthy, and half of whom had already been diagnosed with glaucoma.
Their "intraocular pressure" was measured, then they were asked to put on a "slightly uncomfortable" tie for three minutes.
They were tested again, and 60% of the glaucoma patients, and 70% of the healthy men were found to have significant rises in pressure. As soon as the ties were removed, the pressure fell again.
The experts say that the ties are probably causing the problem because they are constricting the jugular vein, the main blood vessel returning blood from the head towards the heart.
They add that such rises in pressure could also lead to normal, healthy patients being diagnosed as at risk of glaucoma by mistake.
In an article in the Journal of Ophthalmology, the researchers write: "A tight necktie can be considered a risk factor in men who prefer to wear tight neckties, men with thick necks, and white collar professionals."
Professor Neville Osborne, a researcher in eye disease at Oxford University, told BBC News Online that doctors would be advised to ask their patients to loosen their ties before trying to carry out tests.
He said: "It's a very interesting finding. It could well be that the tie is restricting blood flow.
"If there is a rise in intraocular pressure over time, it could cause damage to the retina."