This invention relates to intraocular surgical instruments and more particularly to instruments adapted to vitrectomy surgery that incorporate reciprocating cutters.
It is sometimes necessary to surgically remove a portion of the vitreous body of the eye in order to eliminate opaque regions of the body, blood, retinal tissue and the like. The vitreous body has a jelly-like consistency, requiring that portions to be excised be cleanly cut off from the remaining portion of the vitreous body. One method of severing vitreous portions involves the use of a surgical instrument that comprises coaxial slender tubes and which is inserted into the region of the vitreous to be removed. The outer tube has an orifice with a sharp cutting edge on the internal surface of the tube, while the inner tube has a sharp cutting edge formed on its outer periphery. The portion of the vitreous body to be excised is pulled into the orifice in the outer tube by suction applied to the inner tube, and the portion is severed by moving the cutting edge of the inner tube past the cutting edge of the outer tube in a reciprocating fashion.
It is important that the cutting edges of the reciprocating tubes of such instruments fit together closely in order to provide a good cutting action. If the cutting edges do not cooperate properly, there is a danger that a portion of the vitreous body might become trapped between the outer wall of the inner tube and the inner wall of the outer tube. This is a serious problem because tissue that becomes trapped is difficult to cut cleanly away from the remaining vitreous body, and further movement of the instrument may cause tension on the vitreous body that may damage the retina.
Various means have been provided for effecting the proper orientation of the cutting edges of the inner and outer tubes in order to clearly sever the portion of vitreous body to be removed. In most of the prior art devices, this objective is addressed by providing minimal clearance between the internal wall of the outer cutter tube and the external wall of the inner cutter tube along the entire length of their adjacency. While this arrangement helps to ensure the proper orientation of the tubes at the point where the cutting edges meet, it has caused a considerable amount of friction between the two walls.
In an attempt to overcome the problem of friction while retaining a proper alignment at the cutting edges, a longitudinal portion of the outer tube has been cut away between its two ends, as disclosed in U.S. Pat. No. 4,246,902, issued to Martinez. In this fashion, the friction that would have otherwise occurred between the cut-away portion and the inner tube is of course eliminated, but the amount of friction caused by movement of the remaining portions against the inner tube is maintained, and the lessened structural integrity caused by the removal may also be a source of problems. In particular, the cutting away of a large longitudinal portion of one of the cutting tubes may increase the flexibility of that tube to an extent that the precise orientation of the cutting edges is lost.
In addition, prior art devices of this type are generally manufactured in a way that increases the cost of the devices and causes disposability after a single use to be impractical. For example, in U.S. Pat. No. 4,246,902, the device is generally complex and requires a number of threaded parts.