The present invention pertains generally to methods for performing intrastromal ophthalmic laser surgery. More particularly, the present invention pertains to the use of laser surgery to prepare corneal donor plugs. The present invention is particularly, but not exclusively, useful as a method for harvesting corneal donor plugs for use in keratophakia procedures.
The cornea of an eye has five (5) different identifiable layers of tissue. Proceeding in a posterior direction from the anterior surface of the cornea, these layers are: the epithelium; Bowman's membrane; the stroma; Descemet's membrane; and the endothelium. Structurally, the cornea of the eye has a thickness, between the epithelium and the endothelium that is approximately five hundred micrometers (500 μm). Within this structure, the stroma has a thickness of almost four hundred microns in the cornea.
It is well known that defective vision can be corrected by reshaping the cornea of the eye. Further, it is known that reshaping of the cornea can be accomplished in several ways. For example, the well known radial keratotomy procedure is used to establish weakened areas in the cornea which respond to internal pressure in the eye to move the cornea in its optical relationship with the retina. Another way in which vision can be corrected is by procedures which actually remove portions of the cornea to alter its optical properties. Yet another method for vision correction involves the implantation of a synthetic or natural tissue into the patient's cornea to change the curvature of the cornea. Often, implantation is the most suitable procedure for modifying refractive error for patients having thin corneas (corneas with thicknesses less than 450 micrometers). This is particularly so for patient's with thin corneas that are in need of high correction (over ten diopters). In this category of procedures, keratophakia refers to the use of a donor cornea as an implant.
In keratophakia, a plug or button of a donor's cornea is shaped to desired dimensions and is inserted into the recipient's stroma to change its curvature. Typically, a microtome is used to cut into the donor cornea. Then, a single plug is removed from the stroma of the donor cornea and is shaped for use in the keratophakia procedure. While this known method is effective, the use of the microtome typically results in an uneven cutting of the donor cornea and donor plugs with resultant irregular edges. Further, the known method obtains only a single plug from a donor cornea.
In light of the above, it is an object of the present invention to provide methods for photoablating donor corneal tissue to obtain a plurality of donor plugs from a single donor eye. Another object of the present invention is to provide methods for performing ophthalmic laser surgery that optimize the use of donor corneal tissue. Still another object of the present invention is to provide methods for harvesting corneal plugs with even surfaces. Yet another object of the present invention is to provide methods for harvesting corneal donor plugs for use in keratophakia procedures that are relatively easy to implement and comparatively cost effective.
In accordance with the present invention, methods for harvesting a plurality of corneal donor plugs for use in keratophakia procedures are provided. Importantly, for these methods, a perimeter for the plurality of plugs is determined. Preferably, the perimeter is substantially cylindrical and is centered about an axis defined by the donor cornea. Also, a posterior boundary and an anterior boundary for the plurality of plugs are selected. Further, interfaces between adjacent plugs are identified. For the present invention, the boundaries and interfaces are substantially planar and are perpendicular to the axis. Typically, at least two, but as many as four, plugs are harvested from the stroma of a single donor cornea. Thus, with four plugs, three interfaces are identified. Preferably, each plug has a thickness of approximately 100 micrometers. As a result, each boundary is approximately 100 micrometers from the adjacent interface and each interface is approximately 100 micrometers from the adjacent interface.
In general, each method of the present invention requires the use of a laser unit that is capable of generating a so-called femtosecond laser beam. Stated differently, the duration of each pulse in the beam will be less than one picosecond. When generated, this beam is directed and focused onto a series of focal spots in the stroma of the donor cornea. The well-known result of this is a Laser Induced Optical Breakdown (LIOB) of stromal tissue at each focal spot. In particular, and as intended for the present invention, movement of the focal spot in the stroma photoablates the donor cornea along the perimeter, the boundaries, and the interfaces.
In a preferred procedure, the laser beam is operated so that each pulse of the laser beam has an energy of approximately 2.5 microJoules. This laser beam is then directed along a series of focal spots around the perimeter. Thereafter, the laser beam is modified to emit pulses having an energy of approximately 1.8 microJoules. With this lower energy level, the laser beam is directed along a series of focal spots along the posterior boundary, the interfaces, and the anterior boundary. As a result of the photoablation, the plurality of donor plugs is created in the donor cornea. After the plurality of donor plugs are created, they are removed from the donor cornea in a single cohesive unit. Each donor plug may then be mechanically separated from the others, by peeling the donor plugs apart.
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:
Referring initially to
In
After the perimeter 32, boundaries, 36, 38 and interfaces 40′, 40″, 40′″ have been determined, photoablation is performed. Specifically, the laser unit 10 directs a pulsed laser beam 12 to a series of focal points 44 along the perimeter 32 to photoablate the corneal tissue 16 at the perimeter 32. During photoablation of the perimeter 32, each pulse of the laser beam 12 has an energy of approximately 2.5 microJoules. After photoablation of the perimeter 32 is complete, the boundaries 36, 38 and interfaces 40′, 40″, 40′″ are photoablated. During this photoablation procedure, the pulsed laser beam 12 is directed to a succession of focal points 44 along the selected boundary 36, 38 or interface 40′, 40″, 40′″. In
After photoablation is performed, the individual donor plugs 42 are created. The plurality of plugs 30 may be removed from the donor eye 18 in a single unit. Thereafter, individual plugs 42 may be separated from the plurality 30 by mechanically peeling each plug 42 away from the others. Then, each plug 42 may be used independently in a keratophakia procedure. In this manner, a plurality of plugs 30 is prepared from a single donor eye 18.
Referring to
While the particular Method for Harvesting Corneal Donor Plugs for Use in Keratophakia Procedures 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.