a rear - loaded injector cartridge for an intraocular lens having a proximal opening that provides a haptic slot . the haptic slot receives a leading haptic of an iol loaded therein , and temporarily retains the leading haptic while the optic of the iol is inserted into a holding area of the cartridge . as the optic passes by , the leading haptic folds over the top of the optic , on its anterior side . the length of the haptic retention slot is sufficient to maintain the leading haptic in its anteriorly folded position while the iol remains in holding area , typically while the cartridge is mated with a handpiece of the injector . the cartridge also has a rear or proximal cut out which advantageously keys with a similarly - sized rail on the handpiece so that the cartridge cannot be inserted in the wrong way .