A valved trocar cannula for insertion into an eye includes a trocar cannula having a distal end configured to be positioned within the eye and a proximal end configured to be positioned outside the eye. An elastomeric membrane or seal is attached to the trocar cannula at the proximal end thereof and restricts a free flow of fluid from within the trocar cannula to outside the proximal end of the trocar cannula. The elastomeric membrane includes at least one slit extending therethrough and is arranged to permit the passage of a surgical instrument through the membrane and into the trocar cannula. The slit may through the elastomeric membrane at an oblique angle along a least a portion of the slit. Pressure applied across a first surface or a second surface of the elastomeric membrane in a vicinity of the slit tends to keep the slit in a closed position.
