Pressure-volume relation for the living human eye

Purpose. The pressure-volume relation for an eye is the mathematical equati on that relates changes in intraocular pressure to changes in intraocular v olume. This relation is useful for calculating outflow facility from tonogr aphy and pulsatile ocular blood flow from intraocular pressure pulsations. The present work develops a new relation by culling together all the publis hed 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. Th e approach was (i) to perform an error analysis based on the various experi mental conditions, (ii) to assume general mathematical forms for the relati on, (iii) to use least-squares analysis and statistical measures to find th e optimal data representation, and (iv) to introduce the total volume of th e eye into the formulation. Results. A new formula for the pressure-volume relation for the living huma n eye is derived relating DV, the change in volume, to P, the corresponding intraocular pressure: Delta V = V (C + C-0 x ln P + C-1 x P), where V is t he volume of the eye, C, C-0 and C-1 are numerical parameters. This equatio n 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 gi ves a larger volume increment for a given increment of pressure than Friede nwald's equation based on measurements performed on cadaver eyes.