Patent Publication Number: US-2010130967-A1

Title: Method and Apparatus for Enhanced Corneal Accommodation

Description:
FIELD OF THE INVENTION 
     The present invention pertains generally to systems and methods for improving the visual performance of an optical unit. More particularly, the present invention pertains to systems and methods that facilitate the accommodation of a human eye. The present invention is particularly, but not exclusively, useful for systems and methods that alter physical characteristics of the cornea of a human eye, to facilitate accommodation by the lens of the eye. 
     BACKGROUND OF THE INVENTION 
     Ocular accommodation refers to the ability of an eye to change its effective focal length, and to thereby see objects distinctly at varying distances. As is well known, the predominant anatomical mechanism for achieving accommodation involves changes in the configuration of the crystalline lens in the eye. Specifically, this configuration change results from a contraction of the ciliary muscle that causes the curvature of the lens surfaces to increase. There is, however, evidence that additional factors may be involved in accommodation. A recent article by Akihiro Yasuda, Tatsuo Yamaguchi, and Kishiko Ohkoshi, entitled “Changes in corneal curvature in accommodation” suggests that changes in corneal curvature in accommodation, participate in the mechanism of accommodation (see J Cataract Refract © 2003 ASCRS and ESCRS). Accordingly, current thinking is that the physical configurations of both the cornea and the lens of an eye work together with each other for accommodation. 
     With increased age, the crystalline lens of an eye becomes more rigid, and its accommodative amplitude declines. Consequently, the configuration compliance of the cornea with the lens that is required for effective accommodation may be adversely affected. If so, a higher flexibility in the structure of the cornea is needed to facilitate the necessary compliance. 
     It is well known that cornea flexibility can be improved by selectively weakening the cornea in accordance with appropriate diagnostic data. For example, U.S. patent application Ser. No. 12/127,539, which was filed on May 7, 2008 by Bille et al. for an invention entitled “System and Method for Reshaping a Cornea Using a Combination of LIOB and Structural Change Procedures,” and which is assigned to the same assignee as the present invention, discloses weakening of the cornea for improved flexibility. Further, using diagnostic data, it is also well known that mathematical models can be useful for predicting configuration changes of anatomical structures in dynamic situations. For example, U.S. patent application Ser. No. 12/143,600, which was filed on Jun. 20, 2008 by Bille et al. for an invention entitled “Generalized Modeling of the Cornea,” and which is assigned to the same assignee as the present invention, discloses such a use for a predictive mathematical model. 
     In light of the above, it is an object of the present invention to provide a system and method to facilitate compliance between two different elements of an optical unit during changes in the unit&#39;s focal distance. Another object of the present invention is to alter the physical characteristics of a first optical element (e.g. the cornea of an eye) to facilitate its compliance with changes in the physical characteristics of a second optical element (e.g. the lens of the eye), for improved optical performance of the second element (e.g. the lens). Yet another object of the present invention is to provide a patient with a stronger change of focal power during the accommodation process for improved near vision (i.e. improved reading ability). Still another object of the present invention is to provide a system, and its method of use, for improving the accommodation performance of an eye that is relatively easy to implement, is simple to use, and is comparatively cost effective. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a system and method for improving the ocular accommodation of an eye involves facilitating compliance of a first optical element (e.g. the cornea of the eye) with a second optical element (e.g. the lens of the eye). In particular, facilitating this compliance is a consequence of improving the flexibility of the cornea (e.g. first optical element). And, more specifically, it is accomplished by minimizing optical interference of the cornea with the lens. Structurally, the necessary compliance is achieved by weakening a selected portion of the cornea (i.e. first optical element) to achieve optimal accommodation. 
     As a first step in the method of the present invention, at least one physical characteristic of the cornea (first optical element) is measured. For the present invention the physical characteristic is envisioned to be selected from a group consisting of the refraction of an eye, the topography of an eye, the corneal thickness profile of an eye, the wavefront aberrations of an eye, and the biomechanical properties of an eye. Preferably, measurements of the physical characteristic are made on the cornea while the lens transitions through an accommodation range of approximately fifteen diopters. The diagnostic data that is collected during these measurements can then be used as input to a Finite Element Model (FEM). Output from the FEM will be geometric parameters for the cornea that, in turn, can be used to identify required alterations of the cornea to facilitate its compliance with the lens during accommodation. 
     After the diagnostic data has been collected and the geometric parameters have been identified, the cornea can be appropriately altered (i.e. weakened). To do this, in one embodiment of the present invention, a laser unit is used to perform Laser Induced Optical Breakdown (LIOB) in stromal tissue of the cornea. Specifically, this LIOB is accomplished over at least one defined intrastromal surface, such as ring cuts, radial cuts, ring section segments, horizontal layers or combinations thereof. In another embodiment of the present invention, the cornea is weakened by applying a topical medium to selected areas of its anterior surface. In both embodiments, the purpose is to weaken the cornea so it will be more compliant with changes in lens configuration and, thus, improve accommodation of the eye. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which: 
         FIG. 1  is a schematic presentation of a system in accordance with the present invention shown operationally positioned for interaction with an eye (shown in cross section); 
         FIG. 2A  is a top plan view of the anterior surface of an eye as seen along the line  2 - 2  in  FIG. 1  with representative cylindrical intrastromal LIOB cuts shown end-on; 
         FIG. 2B  is a view as seen in  FIG. 2A  showing representative ring segment LIOB cuts; 
         FIG. 2C  is a view as seen in  FIG. 2A  showing representative radial LIOB cuts; and 
         FIG. 3  is a cross section view of the cornea of an eye as seen along the line  3 - 3  in  FIG. 1  showing horizontal layer LIOB cuts in the stroma of an eye. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring initially to  FIG. 1  a system for improving the accommodative power of a focusing unit is shown and is generally designated  10 . As shown, the system  10  includes a laser unit  12  that is positioned to direct a light beam along a beam path  14  toward an eye  16 . Further,  FIG. 1  shows that light reflected from the eye  16  can be directed toward a detector  18  for a diagnostic analysis of the eye  16 . The diagnostic data that is collected and analyzed by the detector  18  can then be used as input to a mathematical model  20 . 
     In accordance with the present invention, the laser unit  12  can be considered as performing two different functions. For one, the unit  12  can function as a light source that is used for generating the diagnostic data. In this capacity, the unit  12  can be any of several type light sources well known in the pertinent art. For another function, the laser unit  12  can function as a surgical laser that can be used to alter stromal tissue within the cornea  22  of the eye  16 . In this latter capacity, the laser unit  12  preferably generates a pulsed laser beam having ultra-short pulses (e.g. femto-second duration pulses). As envisioned for the system  10 , the alteration of stromal tissue will be accomplished by a well known phenomenon generally referred to as Laser Induced Optical Breakdown (LIOB). 
     For the system  10  of the present invention, the diagnostic data that is collected and analyzed by the detector  18  is envisioned to include various anatomical aspects of the cornea  22  of the eye  16 . For example, using wavefront analysis, this data can include refractive properties of the eye  16 , and of the cornea  22 . Also, the data can include the topography of the anterior surface  24  of the cornea  22 , the corneal thickness profile (pachymetry), and wavefront aberrations as well as various biomechanical properties of the eye  16 . Preferably, this data is collected while the eye  16  is caused to experience accommodation through an accommodation range that may be as much as fifteen diopters. In any event, the collected diagnostic data can then be used to determine how the cornea  22  should be altered (i.e. weakened) for purposes of the present invention. More specifically, using the diagnostic data, geometric parameters for structurally altering the cornea  22  are obtained. Preferably, this is done using a mathematical, predictive model such as the finite element model disclosed and claimed in U.S. patent application Ser. No. 12/143,600, and referred to above. 
     For one embodiment of the present invention, the geometric parameters are used to establish patterns of Laser Induced Optical Breakdown (LIOB) in stromal tissue of the cornea  22 . Recall, these parameters are based on diagnostic data and are preferably obtained from the predictive model  20 . In another embodiment, these same geometric parameters can be used to identify selected areas of the anterior surface  24  of the cornea  22  where a topical agent (e.g. an enzyme) can be applied to weaken the cornea  22 , to thereby improve its flexibility. For both embodiments, the object is to weaken corneal tissue for increased flexibility of the cornea  22 . As intended for the present invention, this improved flexibility facilitates accommodation of the eye  16 . 
     Still referring to  FIG. 1 , it will be appreciated that an accommodation mechanism for the eye  16  changes the anatomical configuration of the lens  26  of the eye  16 . As is well known, this configuration change is caused by contractions of the ciliary body (muscle)  28 . The result is a configuration change for the lens  26  that is represented in  FIG. 1  by variations between the configuration of lens  26  (solid line) and the configuration of lens  26 ′ (dashed line). As mentioned above, an accommodation of the eye  16  will typically be within an accommodation range of approximately fifteen diopters. 
     As envisioned for the present invention, accommodation provided by configuration changes of the lens  26  will be facilitated when the cornea  22  complies with these changes. This requires flexibility on the part of the cornea  22 . And, according to the present invention, the necessary flexibility is achieved by weakening selected portions of the cornea  22 . The exact locations for weakening the cornea  22 , and the extent or scope of such weakening will be determined by an analysis of the diagnostic data. Several examples of possible alterations for weakening the cornea  22  are illustrated in  FIGS. 2A-C  and  FIG. 3 . Respectively, these possible alterations include LIOB for rings and cylinders  30  ( FIG. 2A ), ring section segments  32  ( FIG. 2B ), radial cuts  34  ( FIG. 2C ), and horizontal layers  36  ( FIG. 3 ). 
     While the particular Method and Apparatus for Enhanced Corneal Accommodation as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.