Purpose: The pressure-volume relation for an eye is the mathematical equation that relates changes in intraocular pressure to changes in intraocular volume. This relation is useful for calculating outflow facility from tonography and pulsatile ocular blood flow from intraocular pressure pulsations. The present work develops a new relation by culling together all the published direct manometric rigidity measurements on living human eyes.
Methods: A total of 182 data items taken from 21 eyes are available in the 1958-62 literature of Ytteborg, Prijot, Eisenlohr, Langham and Maumenee. The approach was (i) to perform an error analysis based on the various experimental conditions, (ii) to assume general mathematical forms for the relation, (iii) to use least-squares analysis and statistical measures to find the optimal data representation, and (iv) to introduce the total volume of the eye into the formulation.
Results: A new formula for the pressure-volume relation for the living human eye is derived relating DeltaV, the change in volume, to P, the corresponding intraocular pressure: DeltaV = V (C + C(0) x ln P + C( 1) x P), where V is the volume of the eye, C, C(0) and C(1) are numerical parameters. This equation gives the most statistically significant fit to the experimental data.
Conclusion: The new equation for the pressure-volume relation derived from all the currently available ocular rigidity data on the living human eye gives a larger volume increment for a given increment of pressure than Friedenwald's equation based on measurements performed on cadaver eyes.