Pneumatic Retinopexy

Abstract

Pneumatic retinopexy (PR) is an office-based, sutureless, no-incision alternative to scleral buckling or vitrectomy for the surgical repair of selected retinal detachments. Cryotherapy is applied around the retinal break(s) to form a permanent seal. A gas bubble is injected into the vitreous cavity, and the patient is positioned so that the bubble closes the retinal break(s), allowing resorption of the subretinal fluid (Figure 8–1A–F). As an alternative to cryotherapy, laser photocoagulation can be applied after the intraocular gas has caused the retina to reattach. Sulfur hexafluoride (SF6) is the gas most frequently used with pneumatic retinopexy. Perfluorocarbon gases such as perfluoropropane (C3F8) are sometimes used, and success has also been reported with sterile room air. In selecting a gas, it is important to understand the longevity and expansion characteristics of the gases. SF6 doubles in volume within the eye, reaching its maximum size at about 36 hours. It will generally disappear within about 10–14 days, depending on the amount injected. Perfluoropropane nearly quadruples in volume, reaching maximum size in about three days. The bubble will last 30–45 days in the eye. Room air does not expand, but immediately starts to reabsorb. The air bubble will be gone within just a few days (Table 8–1). The initial expansion of SF6 and C3F8 is due to the law of partial pressures and the solubility coefficients of the gases involved. A 100% SF6 bubble injected into the eye contains no nitrogen or oxygen, but these gases are dissolved in the fluid around the bubble. Due to the law of partial pressures, nitrogen and oxygen will diffuse into the gas bubble. SF6 also starts to diffuse out of the gas bubble into the surrounding fluid which contains no SF6. However, nitrogen and oxygen diffuse across the gas–fluid interface much more quickly than SF6 because of the relative insolubility of SF6. The net result is an initial influx of gas molecules into the bubble, expanding its size until partial pressures equilibrate, net influx equals net egress, and maximum expansion is reached. Then the bubble gradually reabsorbs as the SF6 is slowly dissolved in the surrounding fluid.