A biological model of tamponade gases following pneumatic retinopexy.

PURPOSE

Predict the persistence and expansion of intra-ocular tamponade gases used in retinal detachment surgery. Quantify factors that contribute to elevations in the intraocular pressure.

METHODS

We developed a non-equilibrium physiological model of intraocular gas transfer in vitreoretinal surgery. The model was calibrated using published volumetric decay measurements for four perfluorocarbon gases (CF(4), C(2)F(6), C(3)F(8), C( 4)F(10)) injected into the New Zealand red rabbit. We validated the model by comparing predicted and experimental results at different conditions in the rabbit. Using the rabbit results, the model was scaled up to humans.

RESULTS

Predictions of gas expansion, half-life, and intraocular pressure in humans were found to correlate very well with clinical results. Gas transfer in the eye was controlled by diffusion through plasma and membranes. Although intraocular pressure depended on several complicating factors such as the physiological condition of the eye as well as the medications being used, prediction of conditions that favor elevations in intraocular pressure were identified based on the transport and thermodynamic properties of the gases.

CONCLUSIONS

The biological model accurately predicted the dynamics of intraocular gases in the human eye. The major factor affecting the intraocular pressure was the aqueous humor dynamics, which is highly dependent on the physiological conditions in the eye. However, for long duration gases such as perfluoropropane, elevations in intraocular pressure are possible following an increase in volume and/or purity of the injected gas. By injecting a mixture of air with an expansive gas, it is possible to reduce elevations in intraocular pressure in patients with the trade off of a reduced longevity of the gas bubble. For gases that diffuse faster than perfluoropropane, there are minimal effects on intraocular pressure due to these changes.