Fig. 13. Gas-air exchange. A 15% mixture (50 mL) of perfluropropane (C3F8) gas and air is lavaged through a 30-gauge needle. Air is vented from the eye through the infusion cannula, to which a 25-gauge needle is attached to maintain uniform intraocular pressure. The flow of air from the eye is confirmed by bubbles in saline in a glass beaker. (Freeman HM: Current management of giant retinal breaks and fellow eyes. In Glaser BM, Michels RG (eds): Surgical Retina, 1st ed, pp 431–448. St. Louis, CV Mosby, 1989)