Refractive surgery and presbyopia correction using infrared and ultraviolet lasers

Abstract

A method and surgical technique for corneal reshaping and for presbyopia correction are provided. The preferred embodiments of the system consists of a scanner, a beam spot controller and coupling fibers and the basic laser having a wavelength of (190-310) nm, (0.5-3.2) microns and (5.6-6.2) microns and a pulse duration of about (10-150) nanoseconds, (10-500) microseconds and true continuous wave. New mid-infrared gas lasers are provided for the corneal reshaping procedures. Presbyopia is treated by a method which uses ablative laser to ablate the sclera tissue and increase the accommodation of the ciliary body. The tissue bleeding is prevented by a dual-beam system having ablative and coagulation lasers. The preferred embodiments include short pulse ablative lasers (pulse duration less than 200 microseconds) with wavelength range of (0.15-3.2) microns and the long pulse (longer than 200 microseconds) coagulative lasers at (0.5-10.6) microns. Compact diode lasers of (980-2100) nm and diode-pumped solid state laser at about 2.9 microns for radial ablation patterns on the sclera ciliary body of a cornea are also disclosed for presbyopia correction using the mechanism of sclera expansion.

Description

[0001]The questions raised in reexamination request 90 / 006,089, filed Aug. 21, 2001 have been considered and the results thereof are reflected in this reissue patent which constitutes the reexamination certificate required by 35 U.S.C. 307 as provided in 37 CFR 1.570(e), for ex parte reexaminations, or the reexamination certificate required by 35 U.S.C. 316 as provided in 37 CFR 1.997(e) for inter partes reexaminations.<?insert-end id="INS-S-00001" ?>BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The present invention relates to refractive surgical systems using low-power, infrared and ultraviolet lasers in a predetermined scanning patterns in procedures of photorefractive keratectomy (PRK), laser assisted in situ keratomileusis (LASIK) and laser sclera expansion (LASE), a new procedure for presbyopia correction.[0004]2. Prior Art[0005]Refractive surgeries (or corneal reshaping) including a procedure called photorefractive keratectomy (PRK) and a more recent p...

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Benefits of technology

[0021]The other preferred laser parameter of this invention is the laser repetition rate of about (40-500) Hz which will provide reasonable surgical speed and minimum thermal effects. We note that the above preferred two embodiments of the mid-IR spectra, (2.7-3.2) microns and (5.6-6.2) microns are based on the facts that they are the two major water absorption peaks and will result in very efficient corneal tissue removal with minimum thermal damage and precise ablation. We also note that the 6.1 microns spectrum matches the absorption peak of corneal protein. Unlike the UV excimer ArF laser, these mid-IR lasers can be easily delivered through a sapphire fiber at minimum loss.

[0022]In another aspect of the present invention is the use of novel, devices for beam-spot-size control, where variable spot size (VSS) are required for fast, efficient tissue removal in PRK, LASIK and LASE. The VSS can be achieved by either a shutter at a fixed pin-hole size or a motorized electronic shutter for adjustable beam spot. Our objective in the present invention is to use these VSS devices to achieve: (a) large beam spot of about (1.5-2.5) mm for large area ablation at fast speed (shorter than 20 seconds), and (b) small spot of about (0.1-0.5) mm for small area ablation such as that of LASE correction without losing the accuracy.

[0025]We should also notice that the problems of central islands, caused by uneven hydration level and shock-wave on the corneal surface, would be mostly reduced by above-introduced VSS designs and controlling these beams scanning in a counter-directions. Moreover, it is another preferred aspect of the present invention to use a random predetermined scanning pattern such that the thermal effect, shock wave and uneven hydration level on the corneal surface can be minimized. The random scanning can be easily achieved by a software design based on the desired correction profiles which is governed by myopic diopter, ablation zone diameter and the position (coordinate) of each scanning beam on the corneal surface. The pre-calculated positions of each scanning spot can be stored and easily assigned to each scanning spot in a randomized means. Details of the equation describing the refractive corrections can be found in J. T. Lin, “Critical review of refractive surgical lasers” in Optical Engineering, vol. 34, 668-675 (1995).

[0026]It is yet another preferred embodiment of the present invention to provide refractive laser systems which offer a “gas blower”, at a controlled hydration gas mixture or pure predetermined gas of helium or nitrogen, on the corneal surface during the surgery. Controlling the corneal hydration is rather critical to the laser ablation. The hydration control is much more important in IR lasers than in LTV lasers. The gas blower may also reduce the thermal effects on the corneal tissue caused by the mid-IR lasers.

[0028]We should note that the idea refractive surgical laser should perform and achieve: fast procedure to reduce the eye-motion-effects, accurate ablation profile (particularly in the presbyopia small zone application), good clinical results (smooth ablated cornea surface, reduced haze and regression), low system cost and easy maintenance. The proposed novel devices of VSS and the multi-stage ablation patterns described in the present invention provide us a unique means to achieve these objectives.

[0030]The preferred embodiments of the basic coagulation lasers to prevent or minimize the corneal bleeding during the LASE procedures include the following lasers at long pulse duration: (a) visible lasers with wavelength of (500-690) nm, (b) infrared lasers at wavelength of about 1.0, 1.5, 2.0 and 2.9 microns, in which the corneal tissue absorption of these radiation will cause the thermal effects for coagulation to occur.

Problems solved by technology

Moreover, UV laser systems suffer problems such as optical damage of the coated mirrors, unstable and short lifetime of the lasing gases and high cost toxic gas of fluorine (for excimer laser).

Low beam delivery efficiency and complexity of beam uniformity are other drawbacks of UV refractive lasers.

At the present time, there is no any commercial or clinically practical mid-IR refractive laser system been developed based upon the prior arts because of the inherent problems and difficulties to be discussed as follows.

Development of Q-switched Er:YAG system was inherently limited by factors of optical damage of the Q-switching components, coating problems due to strong water absorption, and the low repetition rate Oess than 25 Hz) due to the cooling problems of the laser rod.

To overcome all these inherent drawbacks in an Er:YAG system will not be cost effective and a high maintenance efforts will be required when it is used for refractive surgery.

Another alternative proposed by Lin and Telfail et al., the OPO-laser also had technical difficulties in making a clinically practical system.

At this time only low repetition rate OPO-laser (lower than 30 Hz) at low energy (less than 5 mi per pulse) was tested due to the problems of: low conversion efficiency from near-IR to mid-IR wavelength, crystal and optics coating damage at high power and unstable output IR energy due to cooling problems.

Therefore a practical OPO-laser system for refractive surgery will be either difficult to make or high cost at high maintenance efforts.

In addition to the above-described OPO-laser, the present inventor also had attempt at no success to develop a Raman-shifted laser due to difficulties of: unstable IR output due to Raman gas flow, optical damage of the coated windows and the inherent back scattering of the Raman signals.

Again, a Raman-laser for refractive surgery will be of high cost and difficult to maintain.

In addition the system can not be compact in size due to the one-meter long Raman cell.

Corneal reshaping may also be performed by laser thermal coagulation currently conducted by a Ho:YAG laser (at about 2 microns in wavelength) which however, was limited to low-diopter hyperopic corrections.

These prior arts, however, have drawbacks of being complexity and time consuming surgery and having risk of side effects.

The above described prior arts which are not clinically practical for refractive uses because of the inherent technical problems or being not cost-effective.

One of the critical issues of LASE is the corneal bleeding during the laser “cutting”.

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