Noncontact laser microsurgical method

Details Noncontact laser microsurgical method Noncontact laser microsurgical method

1995-06-07

2001-04-03

Shay, David M. (Department: 3739)

Surgery

Instruments

Light application

C606S002000, C606S003000, C606S010000, C606S017000

Reexamination Certificate

active

06210399

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a microsurgical apparatus and, more particularly, a noncontact laser microsurgical apparatus adapted for use in cornea transplant surgery, keratoplasty, keratotomy, and other corneal surgery techniques.
2. Description of the Related Art
Despite advances in corneal preservation and transplantation techniques, postoperative astigmatism remains the most important complication limiting visual acuity after a corneal transplantation.
In order to reduce such postoperative astigmatism, U.S. patent application Ser. No. 07/056,711 filed Jun. 2, 1987 entitled “A Cornea Laser-Cutting Apparatus”, assigned to the same assignee as the present application, discloses that trephination of either a donor cornea or a recipient cornea may be performed utilizing a laser cutting technique.
During penetrating keratoplasty, it is further necessary for a surgeon to align the circumferences of the donor corneal button and recipient cornea. To this end, there have been recently developed mechanical marking apparatuses such as those described in Pflugfelder et al. “A Suction Trephine Block for Marking Donor Corneal buttons,” Arch. Ophthalmol., Vol. 106, Feb. 1988, and Gilbard et al. “A New Donor Cornea Marker and Punch for Penetrating Keratoplasty,” Ophthalmic Surgery, Vol. 18, No. 12, December 1987.
However, such mechanical marking apparatuses directly contact and distort the cornea such that the marking process is not always precisely accomplished and sometimes results in porstkeratoplasty astigmatism.
In radial keratotomy, mechanical contact type surgical utensils as shown in U.S. Pat. No. 4,417,579 have been used to radially incise the cornea of a patient's eye. This surgical method is apt to cause strain and/or deformation of the cornea, and also results in postoperative astigmatism.
Noncontact microsurgery of the cornea would minimize distortion of the cornea tissue, as occurs in contact-type techniques, and would decrease the likelihood of producing postoperative astigmatism. The use of lasers provides the potential for such noncontact microsurgery.
Excimer lasers have been investigated in the past to produce linear corneal incisions or excisions. The argon fluoride excimer laser emitting at 193 nm has been shown to produce sharp, smooth-walled corneal cuts. More recently, the hydrogen fluoride, Q-switched Er:YAG, and Raman-shifted Nd:YAG lasers emitting at about 2.9 um (micro meters), which corresponds to the peak absorption wavelength of water, have been experimentally used to produce linear corneal incisions or excisions.
Industrial laser cutting by focusing the beam into a ring has been proposed as a method for drilling large diameter holes The axicon, a diverging prismatic lens, has been used for such industrial purposes. An axicon system has been used by Beckman & Associates to study corneal trephination with a carbon dioxide laser. This experimentation is described in an article entitled “Limbectomies, Keratectomies and Keratectomies Performed With a Rapid-Pulsed Carbon Dioxide Laser,” American Journal of Ophthalmology, Vol. 71, No. 6, (June 1971). In this article, Beckman et al. describe the use of an axicon lens in combination with a focusing lens to form an “optical trephine” and perform various corneal experiments with animal's. The diameter of the trephine was governed by the focal length of the focusing lens in these experiments. Therefore, to vary the diameter of the annular beam it was necessary to change the focusing lens which acted to change the width of the annular ring and, thus, varied the amount of tissue incised or excised by the laser. Moreover, changing the focusing lens requires a time consuming process for each patient or donor. In addition, the optical system proposed in the Beckman et al. article requires the use of multiple focusing lenses of different focal length.
Accordingly, it is an object of the present invention to provide a noncontact laser microsurgical apparatus and method of using the same which substantially eliminates strain and/or deformation on a cornea during and after trephination.
Yet another object of the present invention is to provide a noncontact laser microsurgical apparatus and surgical method which is capable of marking a recipient cornea and a donor corneal button with a suture track during keratoplasty, and which incises or excises selected portions of a cornea radially and/or paraxially during keratotomy.
Still another object of the present invention is to provide a noncontact laser microsurgical apparatus and surgical method which is capable of performing thermokeratoplasty for curing corneal refractive error and/or astigmatism of a patient's eye.
It is still another object of the present invention to provide a noncontact laser microsurgical apparatus and method capable of surgically “welding” donor tissue or synthetic material and recipient corneal tissue together thereby eliminating the necessity of suturing the donor and recipient parts to one another in penetrating and epikeratoplasty procedures.
It is still a further object of the present invention to provide a noncontact laser microsurgical apparatus and method wherein selected areas of the cornea may be caused to shrink so as to change the curvature of the natural lens thereby curing or alleviating corneal refractive error and/or asigmatism.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
SUMMARY OF THE INVENTION
To achieve the foregoing objects, and in accordance with the purposes of the invention as embodied and broadly described herein, the noncontact laser microsurgical apparatus of the present invention comprises means for generating laser beams; and means for projecting the laser beams onto a cornea. The projection means defines an optical axis and includes means for converging the laser beams. The projecting means further includes axicon optical means for forming the projected beams into a plurality of paraxially distributed spots on the cornea, and means for varying the radial position of the spots.
Preferably, the converging means includes a focusing lens and the axicon optical means includes at least one multiple-facet prismatic (“MFP”) axicon lens mounted for movement along the optical axis of the projecting means.
The generating means may comprise an infrared pulse laser beam generator with a preferred wavelength of about 1.3-3.3 um. Also, an ultra-violet laser source may be used such as an Argon fluoride laser emitting at 193 nm.
The projecting means preferably includes beam expander means for enlarging the radius of the laser beam emerging from the generating means.
The apparatus may also include aiming means for projecting visible laser beams onto the cornea substantially coincident with the positions at which the laser beams projected through the axicon means impinge the cornea. The optical axis of the aiming means preferably overlaps with at least a portion of the optic:al axis of the projecting means. Preferably, the aiming means includes a visible laser beam source, and a mirror obliquely interposed between the beam expander means and the converging means for reflecting the visible laser beams and allowing the laser beams from the generating means to pass therethrough.
The apparatus of the present invention may also include mask means disposed in the optical axis for selectively blocking portions of the projected laser beams while transmitting the remaining portions of the projected laser beams therethrough. In this manner incisions or excisions in the corneal tissue may be made only in selected areas of the cornea corresponding to the transmitting portions of the mask means.
The present invention also provides a microsurgical method for ablati

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