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I would like to congratulate Theelen et al for their recent article on impact factors on intraocular pressure measurements in healthy subjects,1 and I would like to add a thought. As Theelen and colleagues point out with reference to the literature,2,3 increased pressure in the jugular vein leads to increased brain pressure, and by an increase in the episcleral venous pressure, to an elevation of intraocular pressure. Correspondingly, in a previous study by Teng and associates, it was discussed that a tight necktie may increase intraocular pressure by an increased jugular vein pressure and could affect the diagnosis and management of glaucoma.4 It may be taken into account, however, that the brain pressure and pressure in the cerebrospinal fluid space surrounding the retrobulbar part of the optic nerve are the counter-pressure against the intraocular pressure across the lamina cribrosa.5 If the cerebrospinal fluid space pressure is elevated (as a result of increased jugular vein pressure), the intraocular pressure may also be allowed to be elevated so that the trans-lamina cribrosa pressure difference may remain constant. Independently of the question of whether a tight necktie may or may not increase intraocular pressure, one may assume that if the intraocular pressure gets higher because of an increased jugular vein pressure, it may, at least partially, be balanced by an increase in brain pressure, without increasing the risk for glaucoma.
We thank Dr Jonas for his interest in our work and his important supplements about pathophysiological aspects regarding neck circulation and intraocular pressure. As the optic nerve head is in close contact with both intraocular and subarachnoidal space, one may imagine a disc protecting balance in chronically elevated jugular pressure.1 Short term fluctuations of cervical circulation, as present in our recent study, may not facilitate this guarding benefit.2 Thus, repeated huge variations of jugular pressure can presumably be a risk factor for glaucomatous optic nerve head damage. Obviously, this is not the case in slit lamp adapted measurement of intraocular pressure. Nevertheless, the patient’s neck position during tonometry should be taken into consideration to improve the interpretation of intraocular pressure measurements.