The present invention relates to cataract surgery and, more particularly, to a method and apparatus for liquefying, or gelifying, a hardened, cataractous lens and aspirating the same from an eye. This method and apparatus allows for cataract removal through a very small incision, in either the peripheral cornea or surgical limbus. The unequivocal superiority of this method and apparatus compared to present small incision cataract extraction techniques is that it is non-traumatic to intraocular structures, that it is much easier for the surgeon to perform, and that it allows for a smaller incision.
The lens of an adult human eye is about 9 millimeters in diameter and about 5 millimeters thick. A lens capsule, which is the basement membrane of the lens epithelial cells and which has structural integrity, surrounds the lens. The lens, internal to the capsule, is comprised of a nucleus and a cortex. The cortex is a soft, thin layer which surrounds the centrally located nucleus.
The nucleus is comprised of an outer nucleus and an inner nucleus. The outer nucleus is soft regardless of the age of the patient. The inner nucleus is normally soft until approximately the age of 45. After a person attains this age, however, the inner nucleus becomes progressively harder. In some instances, the inner nucleus becomes very hard. When the inner nucleus is soft and relatively elastic, the lens readily changes shape in order to focus, a process known as accommodation. As one grows older and the inner nucleus hardens, the ability of the lens to accommodate decreases. Glasses can be worn in order to correct this deficiency. Wearing glasses will not, however, correct the vision of a person who has a significant cataract.
An eye becomes cataractous when the lens becomes opaque. Cataracts cause diminished vision. If the degree of opaqueness is significant the cataractous lens may be surgically removed. For many years, the most prevalent surgical procedure for removing a cataractous lens was intracapsular extraction. In an intracapsular procedure, the entire lens along with the capsule is removed. A major drawback with this procedure is that the resulting aphakic (lensless) eye has no capsule. Therefore, because there is no capsule there is no capsular support for a posterior chamber intraocular lens (IOL).
Extracapsular lens removal has rapidly become the preferred method for cataract removal since the advent of intraocular lens implants. With this procedure, the anterior portion of the capsule is cut open so that the cataractous lens can be removed. However, the equatorial and posterior portions of the lens capsule are left intact. Once the cataractous lens nucleus and cortex are removed, the implant can be inserted therein. In traditional extracapsular cataract extraction, the lens nucleus is delivered manually. A drawback of this is that a relatively large incision (from 8 mm to 11 mm) must be made in the limbus in order to remove the cataractous lens. That large of an incision causes a relatively lengthy post-operative healing time and is often the cause of significant surgically-induced post-operative astigmatism.
In recognition of the drawbacks of the aforementioned extracapsular procedure, phacoemulsification was introduced. This technique involves the utilization of an irrigation/aspiration handpiece that has an ultrasonic tip attached to the distal end thereof. See, for example, U.S. Pat. No. 3,693,613. The ultrasonic tip, which is rather sharp and made of metal, vibrates approximately 40,000 times per second in order to break up the lens nucleus into tiny pieces so that these pieces can then be aspirated from the eye. The advantage of phacoemulsification is that it allows lens nucleus removal through a relatively small incision of about 3 mm. The disadvantage, however, is that it has proven to be relatively dangerous since the ultrasonic tip destroys any and all tissue that gets in its way. If the vibrating tip comes into contact with the cornea, iris, or capsule, it can cause serious and permanent damage. Moreover, during the break up of the hard nucleus, a chip can break off and effectuate a tear in the posterior capsule. Another disadvantage of phacoemulsification is that it requires a very high degree of skill, concentration and experience on the surgeon's part for it to be performed well on a consistent basis.
Due to the above, cataract surgeons desire a small incision cataract extraction procedure which is inherently safer and easier to perform than phacoemulsification. U.S. Pat. Nos. 4,078,564, 4,135,516, 4,191,176 and 5,022,413 suggest an alternative method for liquefying the hard nucleus so that the same can be aspirated from the eye. The patents describe a method of liquefying the cataractous lens by injecting a concentrated solution of a lens digesting enzyme onto the lens and thereafter removing the enzyme digested lens material. A drawback with this method is that it takes, at a minimum, 12 to 48 hours for the enzyme to soften the hardened nucleus material. Accordingly, the cataractous lens can not be liquified and simultaneously aspirated from the lens capsule. Furthermore, it is not believed that very hard nuclei would liquefy with this enzyme technique.
Other methods have also been proposed for breaking up the hardened nucleus so that the same can be aspirated. These methods are described, for example, in U.S. Pat. Nos. 4,744,360 and 4,597,388. To Applicant's knowledge, however, none of these methods has ever been successfully utilized.
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