The physical and surgical aspects of silicone oil in the vitreous cavity.

Silicone oil inside the vitreous cavity exerts forces on to the retina as a result of buoyancy, volume displacement, and surface tension. Surface tension rather than viscosity is the key to understanding why the oil seals retinal breaks effectively. The physics of the tamponade was studied quantitatively. Retinal traction can be counteracted by the oil up to a calculated threshold value, depending on the size and shape of the tear, the strength of the surface tension and, most importantly, the distance between the retina and choroid. For a nearly flat retinal hole, the tamponade is very effective. These theoretical results imply straightforward rules for surgery, rules that have been tested in 150 operations. An attempt must be made to fill 100% of the vitreous cavity. Since the air-water boundary has 3 times the surface tension of the water-oil boundary, the most effective procedure is to flatten the retina by means of a fluid-gas exchange and then clamp it in a flat position, implanting the silicone oil. Silicone in the subretinal space or the anterior chamber tends to retract spontaneously, for surface tension causes the smaller bubble to blow up the larger one. Surgical methods are described to make use of it.