Surgery – Instruments – Light application
Reexamination Certificate
2002-05-24
2004-05-04
Gibson, Roy D. (Department: 3739)
Surgery
Instruments
Light application
C606S004000, C128S898000
Reexamination Certificate
active
06730074
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains generally to ophthalmic laser surgery systems and procedures. More particularly, the present invention pertains to a contact lens for use in conjunction with a surgical procedure that allows a surgical laser to be precisely focused at a predetermined location within the cornea of a patient's eye. The present invention is particularly, but not exclusively, useful for creating a corneal flap that can be subsequently used in a surgical procedure to improve a patient's vision by altering the shape of the patient's cornea.
BACKGROUND OF THE INVENTION
There are many surgical procedures in which it is desirable to be able to focus a laser beam at a predetermined location within a patient's cornea with precision and accuracy. One such surgical procedure involves the creation of a corneal flap that can be lifted to expose stromal tissue. Once exposed, the stromal tissue can be vaporized using a laser to reshape the cornea. An example of a procedure that uses a laser beam focused at a predetermined location within a patient's cornea is disclosed in U.S. Pat. No. 4,907,586, which issued to Bille et al. for an invention entitled “Method for Reshaping the Eye”. In greater detail, the above-cited Bille patent discloses the use of a pulsed laser beam for subsurface photoablation of intrastromal tissue. Unlike the excimer laser, the pulsed laser beam, as disclosed by Bille, penetrates corneal tissue and can be focused at a point below the surface of the cornea to photoablate stromal tissue at the focal point. The ability to reach a subsurface location without necessarily providing a physical pathway allows for volumes of stromal tissue having complex shapes to be accurately photoablated, while minimizing the amount of total tissue disrupted.
When considering subsurface photoablation, a general knowledge of the anatomy of the cornea is helpful. In detail, the human cornea comprises various layers of tissue that are structurally distinct. In order, going in a posterior direction from outside the eye toward the inside of the eye, the various layers in a cornea are: an epithelial layer, Bowman's membrane, the stroma, Decemet's membrane, and an endothelial layer. Of these various structures, the stroma is the most extensive and is generally around four hundred microns thick. It happens that the healing response of the stromal tissue is generally quicker than the other corneal layers. Because of the relative abundance of stromal tissue and its healing response, stromal tissue is generally selected for removal in refractive correction procedures.
In detail, the stroma of the eye is comprised of around two hundred identifiable and distinguishable layers of lamellae. Each of these layers of lamellae in the stroma is generally dome-shaped, like the cornea itself, and they each extend across a circular area having a diameter of approximately nine millimeters. Unlike the layer that a particular lamella is in, each lamella in the layer extends through a shorter distance of only about one tenth of a millimeter (0.1 mm) to one and one half millimeters (1.5 mm). Thus, each layer includes several lamellae. Importantly, each lamella includes many fibrils which, within the lamella, are substantially parallel to each other. The fibrils in one lamella, however, are not generally parallel to the fibrils in other lamellae. This is so between lamellae in the same layer, as well as between lamellae in different layers. Finally, it is to be noted that, in a direction perpendicular to the layer, each individual lamella is only about two microns thick.
Another important characteristic of the stroma is the strength of the stromal tissue. In greater detail, the strength of the tissue within a lamella is approximately fifty times the strength that is provided by the adhesive tissue that holds the layers of lamellae together. Thus, much less laser energy is required to separate one layer of a lamella from another layer (i.e. peel them apart), than would be required to cut through a lamella. Along these lines, co-pending U.S. patent application Ser. No. 09/783,665, filed on Feb. 14, 2001 by Bille and entitled “A Method for Separating Lamellae” discloses a method for finding an interface between layers of lamellae for efficient photoablation. As disclosed in co-pending application Ser. No. 09/783,665 (hereinafter Bille '665), a wavefront analyzer in conjunction with an ellipsometer can be used to maintain the focal point of a laser beam on an interface between layers of lamellae during creation of a corneal flap for a LASIK type procedure. Use of this technique to photoablate the entire inner surface for a flap has been disclosed in Bille '665.
A somewhat similar method for creating a LASIK type flap is disclosed in co-pending U.S. patent application Ser. No. 09/997,167, filed on Nov. 28, 2001 by Bille and entitled “A Method for Creating a Corneal Flap”. As disclosed in co-pending application Ser. No. 09/997,167, a periphery for a flap can be created using subsurface photoablation along an interface between layers of lamellae. The periphery, in turn, can be used as a starting point to allow layers of lamellae to be mechanically separated from each other along an interface by simply grasping and peeling the flap away from the remainder of the cornea.
In either of these methods wherein photoablation along an interface is desired, the overall movement of the laser focal point is generally along a curved path that is at a substantially constant depth from the anterior surface of the cornea. Thus, it is generally necessary to provide a system to move the laser focal point along this curved path. As the focal point is moving along the generally curved path, a wavefront analyzer and an ellipsometer can be used periodically to verify that photoablation is occurring on an interface between layers of lamellae. When a photoablation response indicates that photoablation is no longer occurring on an interface, a minor adjustment can be made to the depth of the laser focal point to resume photoablation on the interface.
With this in mind, the present invention is focused primarily on providing systems and methods for moving the laser focal point along the curved path (i.e. along paths that are generally parallel to the anterior surface of the cornea). On the other hand, co-pending applications Ser. Nos. 09/783,665 and 09/997,167 provide systems and methods for making minor adjustments to the depth of the laser focal point to maintain the laser focal point on the interface between layers of lamellae. As such, the contents of co-pending application Ser. Nos. 09/783,665 and 09/997,167 are hereby incorporated herein by reference. It follows from the above discussion that the systems and methods for moving the laser focal point along the curved path must be extremely accurate (i.e. accuracy on the order of ±2 &mgr;m) if these systems are to be used to maintain a laser focal point on an interface between layers of lamellae.
Another factor that must be considered when creating corneal flaps by subsurface stromal photoablation is the elastic compressibility of the lamellae in the cornea. Specifically, it is known that the elastic compressibility of the lamellae varies within the cornea with the elastic compressibility being greatest near the center of the cornea. The consequence of this variation in elastic compressibility becomes significant if the cornea is flattened excessively during subsurface stromal photoablation. During severe flattening of the cornea, the three-dimensional architecture of the lamellae in the cornea becomes distorted. The result of this distortion is that an incision that is made while the cornea is severely flattened changes shape in an unpredictable way when the cornea is relaxed.
Still another factor that must be considered when creating corneal flaps by subsurface stromal photoablation is the beam path of the laser beam. Ideally, all beam paths used to create the flap would be oriented normal to the anterior surfa
Baumeister Klaus
Bille Josef
Loesel Frieder
20/10 Perfect Vision Optische Geraete GmbH
Gibson Roy D.
Johnson Henry M.
Nydegger & Associates
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