Abstract:
A system for correcting presbyopia provides a laser adapted to sculpt the cornea in two concentric zones. The first larger zone is treated with a positive diopter correction to allow eye to focus on near objects. A second smaller zone is then treated with a negative diopter correction to allow the cornea to focus on far objects. In one embodiment, the system directs the laser in a series of collapsing crescents to sculpt the zones.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims priority from U.S. provisional application Ser. No. 60/173,448 filed Dec. 29, 1999; the disclosures of which are incorporated herein by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Technical Field  
           [0003]    The present invention generally relates to a method and system for performing surgery on the cornea to correct vision defects. More particularly, the present invention relates to a system and method for treating presbyopia by altering the light transmitting properties of the cornea. Specifically, the present invention relates to a system and method for altering the shape of the cornea to have two concentric vision zones that allow a presbyopic patient to focus on near items and far items.  
           [0004]    2. Background Information  
           [0005]    The human eye transforms light waves into electrical impulses that are interpreted by the brain. Light waves enter the eye through a transparent cornea. The waves then pass through the aqueous humor and through the pupil. The iris expands or constricts the pupil to allow the proper amount of light to pass to the lens. The light waves then pass through the crystalline lens. The lens is focused with the ciliary muscle so that the light waves are properly focused on the retina. The retina includes light sensitive cells (rods and cones) that transform light waves into electrical impulses. The electrical impulses are transmitted through the optic nerve to the brain. The visual cortex at the back of the brain reconstructs the impulses into an image.  
           [0006]    Presbyopia is a natural condition causing the eye to lose its ability to focus on near objects. Over the past several years, presbyopia has been thought to occur due to the loss of flexibility of the crystalline lens in the eye. Presbyopia has traditionally been treated with reading glasses or bifocals that allow the patient to focus on near objects. Surgical correction procedures have not been attempted because of the understanding that presbyopia occurs because the lens has hardened.  
           [0007]    In recent years, another theory has developed stating that presbyopia is caused by the growth of the lens causing the ligaments to loosen so that they can no longer exert tension on the lens. A surgical correction method has been developed based on this theory wherein tension is re-introduced to the ligaments supporting the lens by inserting implants.  
           [0008]    It is desired in the art to provide a surgical treatment for presbyopia where implants are not required. It is desirable that such a method be as successful and as relatively simple as the widely-used laser refractive surgery methods now known in the art.  
         SUMMARY OF THE INVENTION  
         [0009]    The invention provides a system and a method for treating presbyopia by altering the light transmitting properties of the cornea. The invention provides a method wherein two concentric areas of the cornea are shaped to allow the patient to focus on both near and far objects. The larger area is treated to focus on close objects while the inner smaller area is treated to focus on far objects. The method of the invention may be performed on a system that creates collapsing crescent-shaped eroding laser areas.  
           [0010]    The invention allows refractive errors of the eye to be corrected while also correcting the presbyopic condition of the eye.  
           [0011]    The invention may also be used to treat myopia. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a cross-sectional view of a typical human eye;  
         [0013]    [0013]FIG. 2 is a front elevational view of the cornea of the eye;  
         [0014]    [0014]FIG. 3 is a sectional view taken along line  3 - 3  of FIG. 2;  
         [0015]    [0015]FIG. 4A is a view similar to FIG. 2 showing the first stage of a collapsing crescent laser beam applied to the left side of the cornea;  
         [0016]    [0016]FIG. 4B is a view similar to FIG. 4A showing an intermediate stage;  
         [0017]    [0017]FIG. 4C is a view similar to FIG. 4A showing a final stage of the collapsing crescent laser beam;  
         [0018]    [0018]FIG. 5A is a view similar to FIG. 4A showing an initial stage of the collapsing crescent laser beam applied to the right side of the cornea;  
         [0019]    [0019]FIG. 5B is a view similar to FIG. 5A showing an intermediate stage;  
         [0020]    [0020]FIG. 5C is a view similar to FIG. 5A showing a final stage of the collapsing crescent laser beam;  
         [0021]    [0021]FIG. 6A is a view similar to FIG. 4A showing an initial stage of the collapsing crescent laser beam applied to the top half of the cornea;  
         [0022]    [0022]FIG. 6B is a view similar to FIG. 6A showing an intermediate stage;  
         [0023]    [0023]FIG. 6C is a view similar to FIG. 6A showing a final stage of the collapsing crescent laser beam;  
         [0024]    [0024]FIG. 7A is a view similar to FIG. 4A showing an initial stage of the collapsing crescent laser beam applied to the bottom half of the cornea;  
         [0025]    [0025]FIG. 7B is a view similar to FIG. 7A showing an intermediate stage;  
         [0026]    [0026]FIG. 7C is a view similar to FIG. 7A showing a final stage of a collapsing crescent laser beam;  
         [0027]    [0027]FIG. 8 is a sectional view similar to FIG. 3 showing the cornea after the laser treatment of FIGS.  4 A- 7 C;  
         [0028]    [0028]FIG. 9 is a view similar to FIG. 2 showing the cornea of FIG. 8;  
         [0029]    [0029]FIG. 10 is a sectional view taken along line  10 - 10  of FIG. 9;  
         [0030]    [0030]FIG. 11 is a sectional view similar to FIG. 3 showing the resulting shape of the cornea after the treatment of the present invention; and  
         [0031]    [0031]FIG. 12 is a schematic of the apparatus used to perform the method of the present invention. 
     
    
       [0032]    Similar numbers refer to similar elements throughout the specification.  
       DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0033]    Presbyopia is a condition that affects most human eyes as the eye ages. A typical human eye is depicted in FIG. 1 and is indicated generally by the numeral  10 . Eye  10  includes a lens  12  that focuses light waves on the retina  14 . The light waves enter the eye through the cornea  16  and pass through the pupil  18  to lens  12 . When eye  10  is young, lens  12  can focus light waves on retina  14  from objects that are relatively close to cornea  16 . For instance, the young eye may properly focus on the text in a book  20  that is as close as two inches from cornea  16 . As the eye ages, lens  12  loses its ability to focus on near objects and eventually book  20  must be held ten to twenty inches away from cornea  16  in order for lens  12  to focus on the text. The young eye thus has an ability to focus in the range indicated by the arrow  22 . The old eye  10  can only focus in the range indicated by the numeral  24 . This condition is known as presbyopia and has traditionally been treated by supplying reading glasses to supplement lens  12  allowing eye  10  to focus back into range  22 . One problem with reading glasses is that the wearer of reading glasses loses his ability to focus on far objects while wearing the reading glasses. The method of the present invention alters the shape of cornea  16  allowing eye  10  to focus on near objects as well as far objects.  
         [0034]    The method of the present invention is performed by first determining the shape and focusing ability of eye  10 . Various methods for determining these factors are known in the art and any of the variety of methods may be used to gather this information. For instance, the first step may be to use a phoropter to measure the refractive state of eye  10 . The person performing the method may optionally determine the topography of cornea  16  with a topographer. The pachymetry or corneal thickness may also be optionally measured.  
         [0035]    Performing these steps will determine if eye  10  is presbyopic piano, presbyopic with spherical hyperopia, or presbyopic with spherical myopia. It may also be determined that any of these three conditions is combined with astigmatism. When eye  10  has astigmatism, the astigmatism is first treated using a LASIK algorithm to correct for the astigmatism. The patient then must wait for eye  10  to heal (approximately two months) before the method of the present invention is performed.  
         [0036]    The doctor performing the method next determines an appropriate level of correction that must be applied to cornea  16  to allow eye  10  to focus on objects in range  22 . In the first embodiment discussed below, eye  10  is presbyopic but plano meaning that no correction is needed to achieve 20/20 vision other than the correction for the presbyopic condition. In the preferred embodiment of the invention, two diopters of correction will be used to correct the presbyopic condition. In other embodiments, a different correction may be used. The doctor then selects a central area  30  (FIG. 2) on cornea  16  to perform the initial treatment. In the preferred embodiment, area  30  is a  6 mm optical zone.  
         [0037]    The patient&#39;s eye is first anesthetized as is known in the art. The doctor cuts a flap in cornea  16  as is known in the art so that the actual laser treatment on area  30  is performed under the outer surface of cornea  16  in the corneal stroma. In other embodiments, the doctor may remove a disk from the cornea. The disk is replaced after the cornea is sculpted. The FIG. 3 shows the topography of cornea  16  before the method of the present invention is applied to cornea  16  as identified with solid line  32 . The initial two diopter treatment will change the shape of cornea  16  to that indicated by dashed line  34 . The two diopter treatment steepens the curvature in area  30  so that eye  10  can focus on close objects  20  in range  22 .  
         [0038]    The initial treatment on cornea  16  is performed by eroding area  36  with a laser beam. The boundaries and definition of area  36  is determined using a difference of sphere algorithm or other suitable algorithms known in the art. The resulting area  36  is mathematically defined is a way that a laser can be controlled to remove area  36 . The apparatus to sculpt a cornea with a laser beam is known in the art and is preferably a LASIK laser. One example of an apparatus useful for performing this method is disclosed in U.S. Pat. No. 5,642,287, the disclosures of which are incorporated herein by reference. The preferred treatment for removing area  36  is to sculpt cornea  16  with four sequential collapsing crescent-shaped laser beams. In other embodiments of the invention, area  36  may be removed using different known methods such as a scanning spot or an erodible mask. The collapsing crescent-shaped laser beams are applied to area  30  in four steps. FIGS.  4 A- 7 C show the application of laser beam  40  to area  30  on cornea  16 . The specific sequence of FIGS. 4, 5,  6 , and  7  is irrelevant to the present invention. The order provided in the drawings is provided as an example but it is understood that the doctor may start on the right half, the upper half, or the lower half instead of the left half as shown in the drawings.  
         [0039]    The treatment begins with a half circle-shaped laser applied to the left half of area  30  as depicted in FIG. 4A. The intensity of laser  40  and the amount of time it is applied to area  30  are determined by a controller that analyzes area  36  and determines the time and intensity required for laser  40  to remove area  36 . Laser  40  then collapses from the shape shown in FIG. 4A towards the shape shown in FIG. 4C. It is thus understood that the size of laser  40  gradually collapses until it disappears in the direction from the center of area  30  to the edge of area  30 .  
         [0040]    The doctor then treats the right side of area  30  as depicted in FIGS.  5 A- 5 C. Once the left and right sides of area  30  are treated, the doctor changes the laser configuration and treats the top and bottom sections of area  30  as depicted in FIGS.  6 A- 6 C and  7 A- 7 C.  
         [0041]    The resulting cornea is depicted sectionally in FIG. 8. Treated cornea  16  now has a steepened section  50  that allows eye  10  to focus in range  52  that includes most of range  22 , some of range  24 , but excludes the far end of range  24 . The cornea of FIG. 8 is thus myopic because it cannot focus on objects far away from cornea  16 . However, the presbyopic eye can now focus on near objects in range  52 .  
         [0042]    Having created the cornea FIG. 8, the doctor now selects a smaller area  60  that is substantially concentric with area  30 . In the preferred embodiment of the invention, area  60  is a 4 mm optical zone. The doctor applies a treatment to area  60  that allows area  60  to focus on objects far away thus treating the myopic condition. This treatment is a spherical diopter correction equal to, but negative of, the positive correction applied to area  30 . In this embodiment, a negative 2 diopter correction is performed in area  60 .  
         [0043]    The negative correction applied to area  60  will remove area  62  of cornea  16  to provide a central area of eye  10  that will be able to focus on far objects. Material  62  is defined and removed using one of the same methods described above.  
         [0044]    The resulting cornea is depicted in FIG. 11. Cornea  16  has a central area  70  that is configured to allow eye  10  to focus on far objects and a ring-shaped area  72  that allows eye  10  to focus on near objects. Having undergone this treatment, the presbyopic patient can now focus on near and far objects without the use of implants or reading glasses.  
         [0045]    As noted above, the initial examination of eye  10  may determine that eye  10  is hyperopic or myopic. When eye  10  is hyperopic, the correction described above is altered to also correct for the hyperopia. For instance, zone  30  is initially treated with a two diopter correction for the presbyopia along with a correction for the hyperopia. In one example where the hyperopia is plus three diopters, the correction first applied to area  30  is plus three diopters for the hyperopia and plus two diopters for the presbyopia resulting in a positive five diopter spherical correction in zone  30 . Zone  60  is then treated with a negative two spherical diopter correction resulting in a correction of the hyperopia in addition to the presbyopia.  
         [0046]    When eye  10  is myopic, the initial correction to area  30  includes a combination of the presbyopic correction with a myopic correction. For example, when eye  10  is negative 3 diopters myopic, the presbyopia correction to area  30  is a negative 1 diopter correction in area  30  determined by combining a negative 3 diopter spherical correction with a positive 2 diopter spherical correction. Area  60  is then treated with a negative 2 spherical diopter correction.  
         [0047]    After the sculpting operations are performed, a topography of the sculpted eye may be taken to show the difference of curvature in zones  60  and  30 . The doctor then examines the patient&#39;s distance visual acuity and checks the patient&#39;s near visual acuity. If further errors are found, further sculpting is performed.  
         [0048]    The apparatus used to perform this method includes a computer  80  that is capable of controlling a laser  82  used to ablate cornea  16 . Computer  80  is capable of controlling laser  82  to define and remove areas  36  and  62 . Computer  80  may include an input device  84 , such as a keyboard, that allows information about eye  10  to be placed in the memory of computer  80 . A controller  86  may also be provided that allows computer  80  to communicate with laser  82 .  
         [0049]    The method and apparatus described above may also be used to treat a myopic cornea. In this treatment, distance is treated in the center and the periphery is treated less to create a solution for the myopic eye. For instance, a 4 millimeter center area may be treated to view distant objects. The peripheral region (outside diameter of 6 millimeters) is treated with a corresponding treatment to allow the eye to see near objects. The 6 millimeter zone is treated first by creating a curvature allowing the 6 millimeter zone to see near objects. A 4 millimeter zone is then treated to flatten the 4 millimeter zone so that it may focus on far objects. The combined zones allow the cornea to focus on near and far objects.  
         [0050]    In the foregoing description, certain terms have been used for brevity, clearness, and understanding. No unnecessary limitations are to be implied therefrom beyond the requirement of the prior art because such terms are used for descriptive purposes and are intended to be broadly construed.  
         [0051]    Moreover, the description and illustration of the invention is an example and the invention is not limited to the exact details shown or described.