The present invention relates to improved surgical instruments for use in ophthalmic surgery, particularly microsurgical cutting probes used to remove the vitreous from an eye. 
There are ophthalmic surgical procedures which require the removal of all or a part of the vitreous humor in the eye.  The vitreous humor (or "vitreous") is a colorless transparent jelly-like material that fills the area of the eye posterior to the crystalline lens.  The vitreous is filled with numerous fiber-like materials which are often attached to the retina.  Removal of the vitreous is difficult due to the presence of the fibers and the possibility of detachment of the inflexible and very delicate retina. 
The present invention provides an improved microsurgical cutting instrument with an elongated needle or probe which is adapted to cut the fibers within the vitreous and remove the vitreous from the eye.  The vitreous is removed primarily through the use of a suction through the hollow probe needle which is inserted through an incision in the eye, under the direction of a surgeon using a microscope.  A unique and advantageous cutting mechanism is contained at the outer end of the probe needle and cuts the fibrous material as the vitreous is being aspirated through the needle. 
During ophthalmic microsurgery, several surgical probes and instruments are used, such as cutting tools and irrigation/aspiration instruments.  The surgical systems also contain a switch or switches (usually foot activated switches operated by the surgeon) controlling the suction and liquid flow and a remote base unit which houses the suction and pumping mechanisms and containers for storing irrigation liquid and collected material.  The ophthalmic surgeon controls the positioning and functioning of the instruments in the eye through the use of a microscope. 
The basic concept and operation of a vitrectomy probe combines a constant suction with a repeated cutting motion of a blade.  The probe comprises a stationary outer needle which contains one or more apertures to receive the vitreous when suction is applied.  A cutting blade located within the outer needle cuts the fibers of the vitreous as it is drawn into the needle.  Various types of cutting mechanisms are known today including rotating or reciprocating blades. 
Since some of the fibers contained within the vitreous are attached to the retina, any incomplete cutting of the fibers could create retinal traction which could lead to retinal detachment.  Incomplete cutting may result from a dull cutting blade, wherein the blade would merely pull the fibers and increase the retinal traction, or from a poor interface of the cutting edges of the outer needle and the cutting blade wherein the shearing effect of the edges passing across one another is reduced.  In addition, imperfect alignment of the cutting blade within the outer tube would cause the shearing action to be localized at the center of the cutting edges and prevent the outer portions of the cutting edges from interfacing sufficiently close enough for a clean shearing action to occur.