One eye of 18 normal and 19 primary open-angle glaucoma patients was included in this prospective study. The intraocular pressure of each patient's randomly selected eye was measured with the patient dressed in an open shirt collar, again 3 minutes after their collar was fastened and necktie tightened, again after a further 12 minutes, and finally 3 minutes after the necktie was loosened and collar unfastened. The same examiner performed all measurements in a masked fashion.