OPHTHALMIC LASERS FOR THE NEXT MILLENNIUM

Ophthalmologists, with respect to both therapeutic and diagnostic applications, have traditionally been at the forefront of laser technology. The proliferation of new technologies and the ingenious application of these technologies over the last several decades ensures that ophthalmologists will continue to be at the vanguard of laser technology well into the next millennium. This article reviews both past and present applications of laser technology and provides an overview of future developments in laser technology within the field of ophthalmology. The history of lasers dates to 1960, when the first functioning laser was demonstrated by Maiman. 76 It was not until 1963 and 1964 when Campbell 19 and Zweng, 141 respectively, reported the first clinical ophthalmic use of a laser in humans, however. They employed a pulsed ruby laser for retinal photocoagulation. They found that laser photocoagulation was efficient, effective, and did not require anesthesia or akinesia. They found that the use of a pulsed laser led to the formation of retinal hemorrhages and had difficulty producing full-thickness retinal burns; this led to the development of continuous wave, gas ion lasers. In 1964, the argon laser, which provides an emission spectrum that is well absorbed by hemoglobin and is used in a continuous mode, was developed. L'Esperance conducted the first human photocoagulation trial for ophthalmic disease using the argon laser in 1968 69 ; he also introduced the frequency-doubled neodymium:yttrium-aluminum-garnet (Nd:YAG) and krypton lasers in 1971 and 1972, respectively. The use of Q-switched and mode-locked Nd:YAG lasers in 1980 and 1981, respectively, provided the ability to produce short bursts of energy that allowed transparent membranes (vitreous, posterior capsules) to be cut. The tunable dye laser was introduced in 1981 and provided the theoretical advantage of a variable output wavelength to match the absorption spectra of specific ocular tissue. The semiconductor infrared diode laser was developed in 1962. Since then, the diode laser has been employed in multiple delivery modes: transpupillary slit lamp, transpupillary laser indirect, transcleral, and endophotocoagulation. It has proven useful in the treatment of choroidal neovascularization, proliferative diabetic retinopathy, retinopathy of prematurity, macular edema, and choroidal melanoma. 84,103 The midinfrared CO 2 laser was developed in 1964 and has been used to perform corneal ablations. 102 This application has been limited by tissue shrinkage and thermal damage to surrounding tissue. 57 In the 1980s, the CO 2 laser was used in skin resurfacing and is now a common technique of rhytid and scar removal. More recently, the CO 2 laser has been used to perform soft-tissue incisional surgery, such as for incisional blepharoplasty. A variety of excimer lasers have been developed. These lasers are capable of emitting pulses of 10 ns and the active medium consists of an excited rare-gas atom with a halogen molecule, resulting in an excited dimer, or excimer. 18 The initial use of the excimer laser, in the early 1980s, was to precisely etch submicrometer patterns into polymer materials for use in the semiconductor industry. 31,61 Srinivasan 120 has termed this controlled removal of material, in which molecules on the irradiated surface are broken into small volatile fragments, ablative photodecomposition. The first ophthalmic use of the excimer laser was reported in 1983 by Trokel, who used the excimer laser to achieve precise etching of the cornea. 130 Since then, a wealth of activity has centered on corneal ablation by the excimer laser, leading to the current interest in laser refractive surgery. A host of new lasers, such as the erbium:YAG (Er:YAG), Q-switched 532 nm Nd:YAG and holmium:YAG lasers promise either improvements in current techniques or novel applications. These new laser techniques may widen the indications for refractive surgery, improve outcomes in glaucoma surgery, obviate the need for vitroretinal surgery in some cases, improve outcomes in oculoplastic procedures, and even help to remove cataracts. Table 1 describes these new ophthalmic lasers and their associated features. Table 2 lists novel applications of existing laser technology.