The human eye in its simplest terms functions to provide vision by transmitting and refracting light through a clear outer portion called the cornea, and further focusing the image by way of lens onto the retina at the back of the eye.  The quality of the focused image depends on many factors including the size, shape and length of the eye, and the shape and transparency of the cornea and lens. 
When trauma, age or disease cause the lens to become less transparent, vision deteriorates because of the diminished light which can be transmitted to the retina.  This deficiency in the lens of the eye is medically known as a cataract.  The treatment for this condition is surgical removal of the lens and implantation of an artificial lens or IOL. 
While early IOLs were made from hard plastic, such as plymethylmtharcrylate (PMMA), soft foldable IOLs made from silicone, soft acrylics and hydrogels have become increasingly popular because of the ability to fold or roll these soft lenses and insert them through a smaller incision.  Several methods of rolling or folding the lenses are used.  One popular method is an injector cartridge that folds the lenses and provides a relatively small diameter lumen through which the lens may be pushed into the eye, usually by a soft tip plunger.  The most commonly used injector cartridge design is illustrated in U.S. Pat.  No.  4,681,102 (Bartell), the entire contents of which is incorporated herein by reference, and includes a split, longitudinally hinged cartridge.  Similar designs are illustrated in U.S. Pat.  Nos.  5,494,484 and 5,499,987 (Feingold) and U.S. Pat.  Nos.  5,616,148 and 5,620,450 (Egales, et al.),  the entire contents of which are incorporated herein by reference.  In an attempt to avoid the claims of U.S. Pat.  No.  4,681,102, several solid cartridges have been investigated, see for example U.S. Pat.  No.  5,275,604 (Rheinish, et al.)  and U.S. Pat.  No.  5,653,715 (Reich, et al.),  the entire contents of which are incorporated herein by reference. 
These prior art cartridges all have a smooth, round or elliptical bore that is symmetric about the longitudinal axis.  While a smooth round bore works well with elastic materials such as silicones and hydrogel, viscoelastic materials such as soft acrylics do not roll or fold as easily, and preferably are rolled or folded more gradually to help prevent damage to the optic and/or haptic. 
Accordingly, a need continues to exist for an IOL injector cartridge that gently folds the IOL.