Abstract:
A transparent flexible shield is provided to protect the outer portions of the cornea and the under surface of a cap of the cornea during LASIK surgery comprising a transparent annular body with a central opening. The central opening is sized to be a little smaller than the outer diameter of the cut made to form the cap. The shield is positioned on the upper surface of the cornea and the folded cap to protect the outer edges thereof from exposure to the ray of the laser.

Description:
This is a continuation-in-part of my application filed Jun. 18, 1998 and assigned Ser. No. 09/336,879, now U.S. Pat. No. 6,349,726. The present invention relates to laser surgery for correcting myopia and hyperopia and in particular to a shield to protect the peripheral portions of the cornea from the laser during the course of such surgery. 
    
    
     BACKGROUND OF THE INVENTION 
     Laser surgery can be used to remove portions of the cornea of the eye thereby reshaping the cornea to correct myopia and hyperopia. During such surgery, a portion of the cornea is removed by the laser thereby reshaping the surface of the cornea to change the focal length of the lens to compensation for the effects of myopia and hyperopia. 
     To undertake such surgery, it is desirable to remove the upper surface of the cornea such that the lower portion of the cornea is exposed to the laser during surgery. After the laser has reshaped a lower portion of the cornea, the upper surface is replaced and eye is allowed to heal. 
     A preferred procedure known as Laser Assisted Interastromal Keratomileusis, commonly known as “LASIK”, involves the cutting of a dome shaped cap from the cornea with a portion of the cap still attached to the cornea to form a hinge. The cap is then folded backwards to expose a lower portion of a cornea. The laser is then used to reshape the lower portion of the cornea, and after the lower portion has been reshaped the cap is repositioned and allowed to heal. The procedure is described in Dishler U.S. Pat. No. 5,807,380. The surgery is carried out by a pre-programmed computerized laser controlled by the surgeon who must be able to see the surface of the eye during the surgery. 
     During LASIK surgery, the laser beam should be directed at only the lower portion of the cornea exposed after removal of the cap, and it is undesirable for the laser to strike the peripheral edge of the opening formed when the cap has been removed or the fold which constitutes the hinge allowing the cap to be folded backward. It would, therefore, be desirable to provide an improved method and apparatus for protecting the vulnerable portions of the cornea from damage by the laser during laser surgery. It is also be desirable that the apparatus obstruct as little as possible of the surgeon&#39;s vision during the surgery. 
     SUMMARY OF THE INVENTION 
     Briefly, the present involves an apparatus and a method of performing laser eye surgery comprising the steps of cutting a cap a material from the outer surface of the cornea of the eye to form a flap having given outer dimensions and a joined edge forming a hinge. The cap is then folded backwards along the joined edge to expose the lower portion of the cornea which is to be re-contoured by the beam of a laser. 
     In accordance with the invention, an annular shield is provided having a central opening with dimensions which do not exceed the given dimensions of the perimeter of the cap and having a concave lower surface which is complimentary to the shape of the outer surface of an eye. Preferably, a plurality of such shields are provided, with each of such shields having a different sized central opening such that a shield having a central opening sized to best fit the size of the lower portion of the cornea under the cap can be selected for use with the eye undergoing surgery. 
     The annular shield is positioned with the lower surface thereof upon the portion of the eye surrounding the cut forming the cap and over the folded flap with the lower portion of the cornea exposed through the central opening. Thereafter, the laser beam is directed through the central opening to perform the surgery. When the shield is made of a rigid material, the shield&#39;s lower surface is concave and complementary in shape to the outer surface of the eye. 
     In accordance with one embodiment of the invention the shield is made of a flexible and transparent material. Flexibility allows the shield to conform to the shape of the eye and to thereby rest comfortably on the upper surface of the eye and thereby not cause injury to the eye. Flexibility also permits a portion of the shield to rest on the upper surface of the eye while a another portion thereof rests on the fold of the cap. The transparent shield creates minimal obstruction to the physician&#39;s view of the eye during the surgery. 
     In the preferred embodiment, the central opening comprises an arc of approximately 270 degrees of a circle and the remaining 90 degrees is a cord connecting the distal ends of the partial circle. Since the shape of each patient&#39;s eye is different, a plurality of shields, each with a different sized central opening, are provided such that a shield having the central opening suitable for use during the surgery of any eye shape is available for use. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A better understanding of the present invention will be had after a reading of the following detailed description taken in conjunction with the drawings wherein: 
     FIG. 1 is a fragmentary isometric view of an eye having a cap removed from the upper surface of the cornea to expose a lower portion thereof; 
     FIG. 2 is a front elevational view of a shield in accordance with the present invention fitted over an eye having a flap folded backwards and the lower portions of the cornea visible through the central opening of the shield; and 
     FIG. 3 is a cross sectional view of the shield shown in FIG. 2 resting on the surface of an eye having a cap removed as shown in FIG. 1; 
     FIG. 4 is a front elevational view of a set of three shields of the type shown in FIG. 2, each with the central opening of each defining a different central diameter. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1 to  3 , in accordance with the LASIK procedure, a dome shaped cap  10  is removed from the cornea  12  of an eye  14  by making a semi-circular peripheral cut  16  which does not close to a circle as shown. The uncut portion  18  serves as a hinge to permit the cap  10  to be folded away from the center of the cornea and leave exposed a lower layer  20  the cornea. In accordance with the LASIK procedure, the upper surface of the lower layer  20  is reshaped by subjecting the cornea to a precision operated laser  21 . 
     It is desirable to apply the laser  21  to the lower layer  20  without subjecting any of the upper surface of the cornea  12  which surrounds the cut  16 , or the under surface  22  of the cap  10  to the rays thereof A complicating factor in the problem of protecting the surrounding cornea and the under surface  22  of the cap is that there are minor differences between the shapes of the eyes of patients, and, as a result thereof, the outer diameter  24  to the cap  10  is different from one patient to another. Another complicating problem is that when the cap  10  is folded backwards, as shown in FIG. 3, the uncut portion  18  or hinge of the cap and the cap  10  itself create an elevated mass on the outer surface of the eye  14  which will prevent a shield having a rigid semi-spherical lower surface from resting with its weight thereof applied evenly on the underlying surface. In fact, a rigid shield with a semi-spherical lower surface will rest at an angle such that portions of the shield will be spaced from the surface of the eye, thereby reducing the effectiveness of the shield to obstruct the undesired rays of the laser. A third complicating factor is that a shield made of a non-material such as metal will necessarily obstruct the physician&#39;s view of the surgery being performed. 
     In accordance with the present invention, to protect the portion of the outer surface of the cornea  12  which surrounds the cut  16  and the under surface  22  of the cap  10 , a shield  26  in accordance with the present invention is provided. The shield  26  is generally annual in shape, having a circular outer peripheral edge  28 , and having generally planar upper and lower surfaces  29 ,  30  respectively. 
     There are no fixed requirements for the outer diameter  31  of a shield, but typically, the outer diameter  31  may be approximately 16.5 mm. The inner opening of the shield includes a semi circular arc portion  34  which defines approximately 270 degrees of a circle, and connecting the ends of the semi-circular arc portion is a cord  36  which defines the remaining 90 degrees of the central opening. 
     An important feature of the invention is that the shield  26  is made of a flexible and transparent material. Since the shield  26  is flexible the weight thereof will generally be applied evenly across the underlying surface of the eye  14  and the entire lower surface  30  of the shield  10  will abut either the upper surface of the eye  14  or the lower surface  22  of the cap  10  as shown in FIG.  3 . The effectiveness of the shield is therefore maximized because the edge of the inner opening  34 ,  36  lies against the surfaces to be protected. Also, the shield  26  will cause a minimum of obstruction to the physician&#39;s view of the surgery because it is made of a transparent material. 
     It should be appreciated that the rays of a laser will only penetrate a flexible transparent material to a very shallow depth and therefor the transparent qualities do not compromise the effectiveness of the shield  26  to protect portions of the eye from the rays of the laser  21 . The material is effectively opaque to the laser rays. 
     Referring to FIG. 4, it is desirable to provide a plurality of shields  26 A,  26 B,  26 C in a set  40  with each shield having a central opening defining a different diameter  38 A,  38 B,  38 C. The surgeon can then select a shield from the set  40  which has an inner diameter  38  suitable for use on the eye of a patient who is to receive eye surgery using the LASIK procedure. Preferably, the inner diameters  38  of a semi-circular portion  34  of a set of shields should range from a minimum of 0.50 mm to a maximum of 15.0 mm, with successive shields having a difference in diameter of approximately 0.50 mm. 
     When a suitably sized shield  26  is positioned over the center of the cornea  12 , with the cord  36  positioned along the fold of the uncut portion  18 , only the lower layer  20  can be seen through the central opening thereof. The edge of the cut  16 , the portion of the cornea  12  surrounding the cut  16 , and the under surface  22  of the cap  10  are all visible through the transparent shield  26  and are protected by the shield from the rays of the laser directed at the cornea of the eye. 
     If the shield  26  is to be made of a rigid material the lower surface  30  is preferably concave in shape to conform to the shape of the eye and is polished so as not to cause irritation to the surface of the eye. It should also be apparent that the body of the shield  26  is made of a suitable material which can withstand and absorb the energy of the laser  21  without conducting excess heat to the surrounding eye. 
     While the present invention has been disclosed with respect to a single embodiment, it will be appreciated that many variations and modifications can be made without departing from the true spirit and scope of the present invention. Therefore, it is the intent of the following claims to cover all such modifications and variations which fall within the true spirit and scope of the invention.