Laser in-situ keratomelleusis (LASIK) is a procedure that is widely used for laser eye surgery to correct refractive errors producing nearsightedness, farsightedness or astigmatism. The use of the LASIK procedure requires a mechanical keratome to cut a thin circular flap across the cornea of a patient's eye so that an eximer laser can then be used to remove a calibrated amount of underlying tissue from the cornea to achieve a desired refractive change. The mechanical keratome as presently used comprises a stainless steel knife blade which is rapidly oscillated during use.
Metal cutting blades can have ragged or uneven cutting edges, and can form burrs extending outward from the cutting edge. Metal cutting blades can also dull during surgical use. These defects, if present on the blade's metal cutting edge, can produce incisions that are ragged and uneven and that extend beyond a desired or critical depth. This can be harmful in reducing the precision of the surgical procedure, in increasing the time required for healing after surgery, and in affecting the patient's vision correction as a result of the surgery. To limit these harmful effects, a careful microscopic inspection of the blade's cutting edge during manufacture and before use must be performed which increases the cost of the blades and results in some blades being rejected as unsuitable for surgery. What is needed is a knife blade for keratomy that has a high degree of sharpness, and which can be reliably produced at low cost. Also needed is a knife blade which maintains its sharpness during use, and is not subject to the formation of burrs.
The present invention provides a solution to this problem by providing a cutting blade (i.e. a knife blade) formed of monocrystalline silicon that can be precisely sharpened by anisotropic etching and which, in the absence of any applied coatings, is incapable of developing burrs because of its crystalline nature.
The use of monocrystalline silicon with a {100} substrate orientation for forming a knife blade is disclosed in U.S. Pat. No. 5,579,583 to Mehregany et al. Mehrenany's requirement for a {100}-oriented substrate produces a blade having a cutting angle determined by the intersection of two crystalline planes, with the cutting angle being crystallography fixed at a relatively large blade angle of either 54.7° or 109.4°. These relatively large blade angles are disadvantageous for use in eye surgery since the large blade angles would effectively reduce the sharpness of the blade and would also make it difficult for the delicate cornea flap to easily slide across the blade during cutting.
The use of monocrystalline silicon for forming various types of knife blades is also disclosed in U.S. Pat. Nos. 5,842,387 to Marcus et al; 5,928,161 to Krulevitch et al; and 5,980,518 to Carr et al. None of these references disclose the use of a {211} substrate orientation for forming a knife blade as used according to the present invention. Additionally, none of these references disclose a cutting edge formed in monocrystalline silicon by a pair of substantially planar cutting-edge surfaces aligned along crystalline planes of silicon and intersecting at an angle of less than 30 degrees.
An advantage of the present invention is that a cutting blade can be fabricated that is substantially free from any burrs or ragged cutting edges.
Another advantage of the present invention is that a cutting blade can be formed with a shallow cutting-edge angle of less than 30 degrees, and preferably less than 20 degrees.
A further advantage of the present invention is that the cutting edge of the blade can be coated with a deposited material such as silicon nitride, titanium nitride, tungsten, amorphous diamond or parylene for improved wear resistance, reduced friction or biocompatibility.
Yet another advantage of the present invention is that a plurality of cutting blades can be formed on a single silicon substrate (i.e. a wafer) in a batch fabrication process and then be individually separated.
Still another advantage of the present invention is that single-edged and double-edged cutting blades can be formed according to the present invention.
These and other advantages of the method of the present invention will become evident to those skilled in the art.