Mechanical model of human eye compliance for volumetric occlusion break surge measurements

To develop a mechanical model of human eye compliance for volumetric studies.

Alcon Research, Ltd., Lake Forest, California, USA.

Experimental study.

Enucleated human eyes underwent pressurization and depressurization cycles with peak intraocular pressures (IOPs) of 60 to 100 mm Hg; anterior chamber pressure and volume changes were measured. Average net volume change curves were calculated as a function of IOP for each eye. Overall mean volumes were computed from each eye's average results at pressure points extrapolated over the range of 5 to 90 mm Hg. A 2-term exponential function was fit to these results. A fluid chamber with a displaceable piston was created as a mechanical model of this equation. A laser confocal displacement meter was used to measure piston displacement. A test bed incorporated the mechanical model with a mounted phacoemulsification probe and allowed for simulated occlusion breaks. Surge volume was calculated from piston displacement.

An exponential function, V = C₁ × exp(C₂ × IOP) + C₃ × exp(C₄ × IOP) - V₀, where V, the volume, was fit to the final depressurization curve obtained from 15 enucleated human eyes. The C₁ through C₄ values were -0.07141, -0.23055, -0.14972, and -0.02006, respectively. The equation was modeled using a piston system with 3 parallel springs that engaged serially. The mechanical model mimicked depressurization curves observed in human cadaver eyes.

The resulting mechanical compliance model measured ocular volumetric changes and thus would be helpful in characterizing the postocclusion break surge response.