Method for altering the curvature of the cornea

A method for altering the radius of curvature of the cornea which includes the steps of making incisions into the cornea and affixing a rigid gas permeable contact lens, having predetermined radius of curvature, to the eye to have the cornea conform to the shape of the lens.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to correcting vision defects, such as myopia, and 
more particularly to changing the radius of curvature of the cornea. 
In the normal eye visual perception involves the process of light entering 
the eye, passing through the cornea and lens converging on the retina at 
the back of the eyeball. Electrical impulses then transmit a sharp image 
to the brain. 
The common vision problem myopia, or nearsightedness, is a congenital 
refractive error manifesting itself in the eye's inability to focus light 
images directly on the retina. Due to the eyeball either being too long or 
the cornea too curved, the light rays entering the eye converge in front 
of the retina resulting in the transmission of the brain an "out of focus" 
image ranging in severity from a mild inconvenience to a debilitating 
handicap. Ordinarily, myopia can be corrected by corrective lenses, such 
as eye glasses or contact lenses. However, for many people corrective 
eyewear is a handicap. Also, when the myopia problem of the eye is the 
result of a progressive disease such as keratoconus, corrective eye 
glasses are satisfactory only in the early phases of the disease. Later, 
when the protrusion of the cornea advances further, contact lens fitting 
becomes more and more difficult, ultimately necessitating surgery as the 
only treatment of choice for sight restoration. 
2. Description of the Prior Art 
Various approaches and devices have been utilized by the prior art for 
correcting corneal curvature and associated conditions such as myopia, 
astigmatism and keratoconus. Such approaches included implantation of 
artificial lenses, implantation of donor's cornea, surgical incisions into 
the anterior cornea, radio frequency probes, lasers and the like. 
One very promising surgical procedure for correcting corneal curvature is 
radial keratotomy which consists of a series of microsurgical incisions, 
placed in a radial pattern on the surface of the cornea. The rational for 
the procedure is as follows. The cornea, being of a dome shape, is being 
supported by both the limbus and the intraocular pressure. As a result of 
the microsurgical incisions, the integrity of the cornea decreases 
resulting in stretching and flattening under the influence of the 
intraocular pressure. Although initially there appears to be peripheral 
bulging with central flattening, upon completion of healing the cornea 
becomes smooth, uniform and as strong as it was prior to the operation. In 
reducing the curvature of the cornea the result is an improved focusing of 
the light rays on the retina hence reduction or elimination of myopia. 
There are, however, clinical variables which influence the success of the 
surgical procedure, such as intraocular pressure, the radius of corneal 
curvature and the number of depth of microsurgical incisions made on the 
cornea. The precise measurement of the variables that affect the outcome 
is difficult at best. Often, it becomes necessary to repeat the operation 
in order to further reduce the curvature of the cornea and improve 
"focusing". One of the most sophisticated techniques in controlling the 
clinical variables includes the utilization of a special micrometric knife 
which makes it possible to regulate the incision depth with high 
precision. The necessary depth of the incision is set according to the 
degree of myopia, corneal thickness and rigidity, and corneal curvature 
radius. The expected effect of surgery, given the diameter of the central 
optical zone, number of incisions and their depth, can then be predicted 
preoperatively by a computer. While this surgical procedure utilizing the 
latest instrumental techniques has proved more successful than previous 
techniques, the lack of predictability of the shape and curvature of the 
cornea still persists. Obtaining the proper diopter correction is still 
"an art" and after the healing of the cornea the patient may still be 
required to wear eye or contact lenses. This lack of reliable 
predictability greatly hinders the use of this surgical procedure except 
in serious cases where no other intervention is available. 
It is therefore an object of the present invention to provide a reliable 
method for vision correction.

DESCRIPTION OF THE INVENTION 
Briefly stated, the invention concerns a method of correcting the curvature 
of the cornea comprising the steps of: 
a. making incisions into the cornea using microsurgical technique; 
b. affixing a rigid gas permeable contact lens, having a predetermined 
radius of curvature, to the eye following surgery; 
c. applying light pressure on the contact lens so that the cornea will 
conform to the shape of the lens; 
d. allowing the cornea to heal under the applied pressure; and 
e. after healing, removing the contact lens from the eye. 
In accordance with the present invention, measurements with a Keratometer 
of the corneal curvature is made and the correction factor necessary to 
obtain proper focusing is calculated. Based on the calculated result, the 
corrective corneal lens having the necessary diopter is selected for use 
following the operation. 
The lens used in the method of the present invention should have a diameter 
of between 10.5 to 12.00 mm and should have an aspheric type base curve 
with an optical zone of about 6.0 mm. The optical zone of the lens should 
have sufficient rigidity to resist flexing or warping. 
The lens used in the method of the present invention may be fabricated from 
rigid plastic materials such as hydrophobic acrylic-type polymers as 
polymethyl methacrylate and the like. Lenses of this type have been known 
for many years and their fabrication technique is well known in the prior 
art. 
The lens used in the method of the present invention may also be fabricated 
from semi-rigid polymeric materials such as cellulose acetobutyrate, and 
silicone rubber. 
Soft contact lens materials consisting of hydrogels of hydrophobic polymers 
may also be used for fabricating corrective cornea lenses when the diopter 
required to obtain corrected vision is small. 
The lenses are conventionally made by marching blanks or disks obtained by 
polymerizing a synthetic monomeric composition. The machining operation 
imparts the final shape with the required optical properties to the 
lenses. 
The preferred method of accomplishing the objective of the present 
invention includes cutting out a wedge of the cornea in the flattest 
meridian on both sides of the pupil followed by placing the corrective 
contact lens on the cornea and applying sufficient pressure thereon so 
that the wedges will close. The contact lens may be affixed to the cornea 
surgically (such as suturing) or by bandaging the eye using conventional 
eye bandaging techniques. The number of incisions may be increased when 
necessary to accomodate the cornea upon stretching due to the pressure 
exerted thereon by the contact lens. The number and kind of incisions is 
determined by the operating surgeon from the readings of the keratometer, 
the internal pressure of the eye and other data obtained from the 
examination of the patient's eye. 
The lens is maintained affixed to the patient's eye until the epithelium 
heals, usually within four to six days.