Microkeratome blade

#This invention relates generally to the field of refractive surgery and, more particularly, to microkeratomes used for performing laser refractive surgery.

#The human eye in its simplest terms functions to provide vision by transmitting light through a clear outer portion called the cornea, and focusing the image by way of a crystalline lens onto a retina. The quality of the focused image depends on many factors including the size and shape of the eye, and the transparency of the cornea and the lens.

#The optical power of the eye is determined by the optical power of the cornea and the crystalline lens. In the normal, healthy eye, sharp images are formed on the retina (emmetropia). In many eyes, images are either formed in front of the retina because the eye is abnormally long (axial myopia), or formed in back of the retina because the eye is abnormally short (axial hyperopia). The cornea also may be asymmetric or toric, resulting in an uncompensated cylindrical refractive error referred to as corneal astigmatism. In addition, due to age-related reduction in lens accommodation, the eye may become presbyopic resulting in the need for a bifocal or multifocal correction device.

#FIG. 1 is a schematic representation of a microkeratome that may be used with the invention of the present method.

#FIG. 2 is an enlarged partial side view of the microkeratome blade of the present invention.

#FIG. 3 is a partial cross-sectional view of a human cornea.

#As best seen in FIG. 1, one microkeratome 34 that may be used with the method of the present invention generally includes suction ring 10 sized and shaped so as to affix to eye 12. Ring 10 includes guides 14/16 opposite eye 12 that guide cutting head 40 across ring 10. Ring 10 is connected through translation member 26 to stepper motor 28 for providing linear movement of cutting head 40 across ring 10. Cutting head 40 contains blade 38 that is eccentrically connected to motor 36 contained within housing 42 of microkeratome 34. Microkeratome 34 is well known in the art (see for example U.S. Pat. No. 6,071,293 (Krumeich), the entire contents of which being incorporated herein by reference), and commercially available from sources such as Alcon Laboratories, Inc., Fort Worth, Tex.

#As best seen in FIG. 2, blade 38 generally includes relatively flat side 100, tapered side 110 containing rounded section 112 and blunt tip 114 connecting flat side 100 and rounded section 112. Rounded section 112 generally has a radius of between about 0.025 millimeters and 0.200 millimeters and is rounded through of angle δ of between approximately 5 degrees and 60 degrees. Blunt tip 114 generally has a length L of between approximately 0.001 millimeters and 0.050 millimeters, with between about 0.005 millimeters and 0.025 millimeters being preferred, and is ground at an offset angle Θ relative to rounded portion 112 at between approximately between 0 degrees and 60 degrees, with between approximately between 0 degrees and 20 degrees being preferred. Preferably, rounded section 112 and blunt tip 114 have a textured surface finish. Blade 38 may be made of any suitable material, such as 400 Series stainless steel and may be made using conventional surgical blade manufacturing techniques well known in the art.

#As best seen in FIG. 3, human cornea 200 has several layers. The outermost layer is epithelium 210, followed by Basement Membrane 220, Bowman's Membrane 230, substantia propria or stroma 240, Descemet's Membrane 250 and endothelium 260. The method of the present invention involves the use of microkeratome 34 having blade 38 to remove epithelium 210 and Basement Membrane 220 while leaving Bowman's Membrane 230 relatively intact. The method of the present invention uses microkeratome 34 in a conventional manner well known to those skilled in the art. Preferably, the intraocular pressure of the eye undergoing the surgical procedure is briefly raised to around 80 mm Hg or greater. The oscillation frequency of blade 38 preferably is approximately between 5,000 revolutions/minute and 20,000 revolutions/minute, with approximately between 8,000 revolutions/minute and 14,000 revolutions/minute being most preferred. The speed of blade 38 as it traverses cornea 200 preferably is approximately between 1.0 millimeter/second and 2.0 millimeters/second, with approximately 1.5 millimeters/second being most preferred. As blade 38 approaches cornea 200, blunt tip 114 penetrates epithelium 210 and Basement Membrane 220, but is insufficiently sharp to penetrate Bowman's Membrane 230. As a result, blunt tip 114 and rounded portion 112 scrape along the surface of Bowman's Membrane 230, separating epithelium 210 and Basement Membrane 220 from Bowman's Membrane 230 without damaging Bowman's Membrane 230. Following such separation, Bowman's Membrane 230 and stroma 240 are irradiated as in a conventional laser refractive surgical procedure, see for example, U.S. Pat. Nos. 4,784,135 (Blum, et al.) and 4,903,695 C1 (Warner, et al.), the entire contents of which being incorporated herein by reference.