Physical mechanisms of gas and perfluoron retinopexy and sub-retinal fluid displacement.

Injection of gas into the eye, followed by face-down positioning, is a common protocol for the reseating of the retina in posterior and superior retinal tears and breaks. The physical mechanism by which injected gas helps reattach retinal flaps is often ascribed to the 'buoyancy' force of the injected gas bubble. The various forces at play in this system (surface tension and buoyancy) were calculated and compared. The results are extended to the case in which the retina is intact (pneumatic displacement of blood) and to the use of intraocular perfluoron (n-perfluorooctane). We show that buoyancy forces are applicable only for gas or n-perfluorooctane bubbles that are smaller than the detached retina and that do not invade underneath the retina. For larger bubbles, as is normally used in reattachment protocols, we show that it is the interfacial tension that reattaches the retina. The range of angles within which patients can position, and still maintain a gas-vitreous interface along a tear is calculated as a function of the volume of injected gas and size of the tear. The maximum retinal flap size that can be reattached using surface tension forces is also estimated.