The use of laser light in ophthalmic surgery is extensive. Laser light may be used to join or cut ocular tissues.
The use of laser light to join or weld ocular tissues, such as corneal and scleral tissues, is well known. U.S. Pat. No. 5,290,272 issued to Burstein et al describes a method for joining ocular tissues with laser light having a wavelength in the range of 1400-1900 nm or 2100-2400 nm, and in which the depth of penetration in the tissue is about 0.2-2.0 mm.
The selection of the wavelength is critical, inter alia, for proper penetration of the ocular tissue. Too short a wavelength results in the laser energy not being absorbed as desired in the tissue. The laser energy instead may penetrate the tissue too deeply, thus endangering the lens and the retina. Too long a wavelength results in the laser energy penetrating to a relatively shallow depth in the tissue, resulting in a weak weld.
Burstein et al clearly teach that a carbon dioxide laser, whose wavelength is about 10,600 nm, is not suitable for welding ocular tissue. The failure of carbon dioxide laser light to produce effective welds in ocular tissues is also discussed in other publications, such as R. H. Keates et al, "Carbon dioxide laser use in wound sealing and epikeratophakia", J. Cataract Refract. Surg., 13:290-295 (1987) and R. P. Gallitis, "Laser Welding of Synthetic Epikeratoplasty Lenticules to the Cornea", Refractive and Corneal Surgery, 6:430-436 (1990). Both of these publications report undesirable tissue damage and shrinkage when using a carbon dioxide laser.
However, in general, carbon dioxide lasers are very useful for many surgical operations, as is known in the art, and some are used in ophthalmic surgery as well, such as in lid surgery. It is therefore desirable to overcome the abovementioned drawbacks and to find a method for using carbon dioxide lasers for joining ocular tissue.
The use of laser light to cut ocular tissue is also well known, particularly in extracapsular cataract extraction. Extracapsular cataract extraction is the removal of an opaque lens through the anterior segment of the eye, leaving the capsule which surrounds the lens intact. The opaque lens is replaced by an intraocular lens (IOL), usually placed inside the capsule.
A critical step of extracapsular cataract extraction and intraocular lens implantation is anterior capsulotomy. Anterior capsulotomy is the surgical cutting and removal of a portion of the anterior capsule in order to allow removal of the opaque lens while preserving most of the lens capsule which serves as a barrier for the vitreous of the eye and a support for the implanted intraocular lens.
Traditional surgical techniques used in anterior capsulotomy often are associated with extension of radial tears to the periphery of the capsule. This results frequently in asymmetric fixation of the IOL and numerous other complications, including IOL decentration and inflammatory reaction caused by the contact between the foreign lens material and the delicate uveal tissue.
Since 1986 a new technique has been promoted as the preferred type capsulectomy, namely "continuous curvilinear capsulorhexis" (CCC). The CCC technique generally involves puncturing the anterior lens capsule ("capsulorhexis") at a distance from the center of the visual axis and then cutting a continuous curvilinear central opening for removal of the lens. The round and intact margin of the central opening is meant to assure a consistent, safe and secure placement of the IOL within the capsule. Since the introduction of the CCC technique, the rate of IOL related complications has been reduced and smaller and safer IOL's have been developed.
Anterior capsulectomy and the CCC technique are discussed in various publications, such as M. E. Wilson et al, "Comparison of mechanized anterior capsulectomy and manual continuous capsulorhexis in pediatric eyes", J. Cataract Refract. Surg., 20:602-606 (1994), B. F. Boyd, "Valuable new findings on pathophysiology of cataract/IOL surgery", Highlights of Ophthalmology Letter, Vol. XXI, No. 9, pp. 10-15 (1993) and M. Blumenthal et al, "Lens anatomical principles and their technical implications in cataract surgery, Part I: The lens capsule", J. Cataract Refract. Surg., 17:205-210.
In general, the CCC technique requires manual dexterity and delicate instruments, such as manually using a bent needle (cystotome) or a special capsule forceps.