The vascular basis of the positional influence on the intraocular pressure

Abstract

By measuring intraocular pressure in different body positions from 60 degrees semiupright to 30 degrees head down, a nonlinear relationship between IOP increase and body position was confirmed. IOP postural response in individual subjects was roughly correlated to ophthalmic arterial pressure and to the episcleral venous pressure postural response. In one series of subjects, the episcleral venous pressure increments due to posture wa; parallel to the applanation-indentation disparity in the same individual eyes. Differential tonometry with applanation or indentation procedures under blind conditions gave significantly low indentation readings. It is concluded that IOP postural response depends on arterial and venous vascular changes when subjects move from an erect to a horizontal body position. Blood expulsion from the choroid by indentation tonometry might be the reason that this tonometric procedure does not measure IOP changes based on vascular changes.

Postural variation in intraocular pressure in primary chronic autonomic failure

“…The findings in normal subjects were comparable with other studies reporting small IOP rises when normal subjects move from the sitting or semi-recumbent to the supine position [15,22,23,32]. In AF the larger changes were closely related to the large swings in blood pressure.…”

“…However, as aqueous drainage is relatively slow [7,9,24] this is unlikely to account for the rapid changes seen in this study. These more rapid IOP changes are therefore more likely to be due to direct pressure and volume changes in the vascular compartments within and around the eye [23]. These would include the peri-orbital tissues [14] and the intraocular blood volume, most of which lies in the choroid [20].…”

Postural Variations of Intraocular Pressure - Preflight Experiments for the Di-Mission

“…In longer lasting head-down tilt, howev er, there must be some other factors in fluencing the IOP as the position and thus the hydrostatic pressure is constant while the IOP still rises, probably due to the in creased filling of choroidal vessels leading to a higher secretion rate of aqueous [5], Final ly, the elevated episcleral venous pressure impedes the aqueous outflow [6].…”

Influência da postura na pressão intra-ocular e nos defeitos de campo visual no glaucoma primário de ângulo aberto e glaucoma de pressão normal

“…Foi observado em um estudo 4 , um aumento da pressão venosa episcleral relacionada à mudança de postura e o aumento da pressão venosa episcleral era correspondente ao aumento da PIO medida com tonômetro de aplanação. Quando a PIO foi aferida com tonômetro de identação, essa correspondência não foi constatada.…”

“…A elevação da PIO ao amanhecer, na posição supina, teria relação com mecanismos circadianos e com o aumento da pressão venosa episcleral [4][5] . A variação da PIO entre as posturas assentada e supina em pacientes glaucomatosos, pode ser maior que em indivíduos normais 1 .…”