At first, the only buffer used was air because of the large difference in surface tension towards water. Unfortunately the air is reabsorbed with ease and often fails to remain in the bulb for all the time necessary for healing, and for this reason other non-toxic gaseous substances have been studied, able to remain in the eye for a longer time. Fluorine compounds such as Sulfur Hexafluoride (SF6), or perfluorocarbons as the PerfluoroMethane (CF4), PerfluoroEthane (C2F6), PerfluoroPropane (C3F8) were selected.
The gas is inserted in a compact bubble at the end of the vitrectomy procedure, after a liquid exchange with air. The gases contained in the intraocular bubble are dissolved in the liquids adjacent to it, and leave the eye in time, diffusing into the bloodstream. But there is an opposite path, that is that of the gases contained in the bloodstream that enter the bubble. All this is regulated by the partial pressure of each gas in its environment. In practice, in the case of a bubble of SF6, nitrogen and other components of the air will spread towards the bubble free of these substances, while SF6 will spread to the blood (free of SF6).
The speed of diffusion plays a fundamental role in this mechanism and while the SF6 will slowly emrge from the eye, the faster the dissolved nitrogen in the blood enters the bubble (SF6 has a molecular weight 5 times greater than nitrogen). This involves an expansion of the gas bubble in the eye by the acquisition of nitrogen from the blood, up to a maximum beyond which, being the pressure of nitrogen now equal to that of the blood, can only be reabsorbed. This behavior allows the bubble to remain longer in the eye, but with the drawback of giving in the early stages of expansion possibilities of dangerous hypertones. The disadvantage described can be avoided by creating a bubble of non-pure gas mixed with nitrogen in order to reduce the speed of diffusion.
For each type of buffering the studies reported in the medical-scientific literature identify the most appropriate mixtures to avoid this eventuality.
The buffering gas is inserted into the glass cavity after carefully removing the central and peripheral vitreous, as there is evidence of a risk in infusing the gas directly into the vitreous. Since it is practically impossible to ascertain that the intraocular pressure is correct (20-40 mm Hg), during infusion, it will be necessary to check the correct papillary spraying and any compression of the optic nerve, and if this occurs, suspend infusion immediately. If the eye is tight make sure that there is a way out while injecting the substance to avoid dangerous eye hypertension.