The influence of position on intraocular pressure.

To better understand the relationship of Schi0tz pressure determination (in the recumbent position) to Goldmann applanation pressure determinations (in the sitting position), we studied, the change in intraocular pressure that occurs when a person changes from a sitting position to lying on his back, utilizing applanation tonometry for both positions. The average pressure rise was 0.3 mm. Hg in one series of measurements and 1.6 mm. in a second series. In both series, the standard deviation of the pressure change from the mean was 1.8 mm. Hg, with some individuals exhibiting a marked change in intraocular pressure when they changed position. When subjects turned to lie on their left sides rather than on their backs, there was an additional average pressure rise, but again there was considerable individual variation in the amount of change. The pressure change in patients receiving glaucoma therapy was greater than in patients not on treatment. The amount of pressure change with change of position is sufficiently variable from individual to individual that in critical studies, such as studies of ocular rigidity or in attempts to improve calibration in Schi0tz tonometry or tonography, one should determine what happens in each individual rather than to assume a standard, change in relating measurements in one position with those in another.