History of Lasers
Aaron B. Zimmerman
Neal Whittle
The story of the ophthalmic laser and how light interacts with the eye begins with the ancient Greeks. Socrates postulated that looking at a solar eclipse was probably harmful to the eyes and recommended indirect viewing.1 Unaware of the retinal anatomy and function, he observed what is now known as photoretinitis and photoretinopathy, both of which result from photochemical damage.
The narrative rejoins in the late 1800s, where Max Planck struggled to understand black body radiation and how energy was released in distinct patterns (quanta) relative to temperature. Planck determined that the light energy released from the black body was related to its frequency multiplied by an unknown constant, which he calculated. This theorem was later validated by Einstein in 19052 and the constant would become universally known as Planck’s constant. Then in 1917, based on the quantum theory of energy, Einstein published an article predicting stimulated emission, the lasing mechanism’s fundamental property.
Thirty years later, the German ophthalmologist Meyer-Schwickerath began experimenting with a carbon arc to create thermal lesions on rabbit retinas.3 The carbon arc did not perform as effectively on human eyes, so he created an instrument that condensed sunlight from his clinic’s roof. It was effective but frequently changing weather conditions made the instrument unreliable. In 1951, he presented on using the Beck arc successfully to create thermal retinal lesions on hundreds of patients. Through the use of various light sources, Meyer-Schwickerath was the first to implement photocoagulation on human retinas.4
Prior to the laser’s development, in 1953, a microwave amplification by stimulated emission of radiation device, the microwave amplification by stimulated emission of radiation (MASER), was invented. This validated the concept of stimulated emission as predicted by Albert Einstein back in 1917. The proof that stimulated emission could work for microwaves emboldened researchers to develop a device that would emit visible light. In 1957, Gordon Gould conceptualized and named the light amplification by stimulated emission of radiation (LASER) device and further described the major components, basic construction, and how it would work.5 However, Theodore Maiman, who was working in the laboratories of the Hughes Aircraft Company, is often credited with developing the first working LASER device in May of 1960.6 This particular device was named the ruby laser (Fig. 1.1) and emitted a wavelength of 694.3 nm. Though he did not
develop the first functioning laser, Gould had attempted to patent the laser concept and was eventually awarded multiple patents after decades of legal challenges.
develop the first functioning laser, Gould had attempted to patent the laser concept and was eventually awarded multiple patents after decades of legal challenges.
 FIGURE 1-1 Theodore Maiman’s ruby laser. The solid ruby crystal is stimulated by the flashbulb that is coiled around it. Source: United States Department of Energy. Campbell EM. Laser programs, the first 25 years, 1972-1997. United States: n.p., 1998. Web. doi:10.2172/16710. Available at: https://www.osti.gov/servlets/purl/16710 |
Later in 1960, the helium-neon laser was invented by Ali Javan,7 and in 1962, quotient switching (Q-switching) technology was available, which allowed lasers to produce extremely large pulses of energy.8 Lasers were quickly being adopted for uses such as range finders, excitation mechanisms for other lasers, and for ophthalmic purposes. The application of using the laser on rabbit retinal tissue was reported by Zaret et al.9 in 1961 and Kapany in 1963.10 Documented use of the ruby laser on human retinal tissue was reported by Flocks and Zweng in 196411 and by L’esperance in 1966.12 The rapid expansion of laser applications increased the likelihood of an adverse event, and in 1964 the first documented laser eye injury occurred in a research lab. The first documented laser eye injury occurred in a research lab in 1964.13
As use of the ruby laser for retinal procedures was explored, Palanker et al. described that the red wave length was not well absorbed by blood—which limited its efficacy, and the laser was very intense resulting in strong chorioretinal adhesions.14 Fortunately, in 1964 the argon laser was invented and this would eventually replace the ruby laser as it was much more effective for retinal procedures. The year of 1964 also saw the invention of the carbon dioxide laser and another prominent ophthalmic laser, the neodymium yttrium aluminum garnet (Nd:YAG) laser. The xenon excimer laser was developed in 1970, the Q-switched Nd:YAG in 1977, and the femtosecond in 1990. Each ophthalmic laser, their applications, and major associated milestones will be further discussed in the following section.
ARGON LASER
In 1964, William Bridges developed the argon laser, which, rather than relying on a crystal as the ruby laser did, relied on argon gas as the lasing medium.15 The argon laser can produce two wavelengths: one is 488 nm and the other a 514-nm band. Due to the emitted beams’ blue and green color, this energy could be more effectively absorbed by the retina, which led to its immediate adoption for retinal surgical applications. Numerous publications were produced in the late 1960s and early 1970s, describing the merits of argon laser retinal surgery. Since 1970, the use of continuous wave lasers, such as the argon laser, has been widely accepted for treating retinal vascular conditions.14
In the late 1960s and into the 1970s, individuals began exploring how lasers could be applied to anterior segment structures such as the iris and anterior chamber angle. In 1967, Snyder used the ruby laser to study laser peripheral iridotomy on rabbit irises. He determined that the laser parameters available at that time would allow for either successful iridotomy with associated retinal damage, or minimal retinal damage but with a lower successful iridotomy rate. Beckman and Sugar performed further investigation in 1973, by comparing how effective the ruby, Nd:YAG, and argon lasers were for producing a laser iridectomy.16 While their results suggested that the ruby was superior to the other two, Khuri successfully created laser peripheral iridotomy (LPI) in rabbit irises through the use of the argon laser.17 Then in 1975 Abraham and Miller further described successful LPI procedures through the use of the argon laser.18
Primitive laser-induced procedures to the trabecular meshwork were first attempted in Russia by Krasnov, where he used a Q-switched ruby laser to “puncture” the trabecular meshwork.19 In the United States, Worthen and Wickham performed trabeculotomy on monkeys using the continuous-wave argon laser.20 In 1979, using a very similar procedure to modern-day argon laser trabeculoplasty (ALT), Wise and Witter successfully demonstrated on 41 eyes that argon laser modifications to the angle could reduce intraocular pressure (IOP) for at least three months.21 In 1981, Wise published an article explaining that the argon trabeculoplasty effects lasted for much longer than three months.22 Further refinements of ALT were proposed by Schwartz & Spaeth, which included reducing the extent of treatment from 360° to 180°.23 As adoption of the technique increased, the National Eye Institute funded the Glaucoma Laser Trial (GLT). The initial report from the GLT was published in 1989 and discussed the acute effects of ALT.24 Multiple publications between 1989 to1995 were produced by this group. The overall conclusion was that initial treatment with ALT was as efficacious as topical medication.
Early attempts at separating the iris root from the angle, modern-day argon laser peripheral iridoplasty, was recorded in 1977.25 The initial technique was performed using a Q-switched laser and with iris-penetrating lesions for 90° of the angle. In 1979, Kimbrough et al. described the argon laser being applied to the peripheral iris to “shrink” the stroma, resulting in less occlusion of the trabecular meshwork.26 The procedure was further perfected by Ritch in 1982.27
Today, the argon laser is becoming increasingly more difficult to find. With the development of the frequency-doubled Nd:YAG and other diode lasers, it is no longer necessary to use the relatively large argon laser. Though the argon laser is slowly going extinct, the names of surgical procedures such as argon laser peripheral iridoplasty, ALT, and argon peripheral iridotomy persist.
NEODYMIUM: YTTRIUM ALUMINUM GARNET
The Nd:YAG laser, invented by Geusic, Marcos, and Van Uitert in 1964 while working at Bell Labs,28 uses a synthetic crystal as the laser medium. The Nd:YAG laser, when first developed, was a continuous-wave laser emitting a 1064-nm infrared beam. Today, the Q-switched Nd:YAG is an extremely common ophthalmic laser as it is routinely used for posterior capsulotomies and laser peripheral iridotomies. Although Q-switching was discovered in 1962 by McClung and Hellwarth8 and the Nd:YAG was discovered in 1964, the ophthalmic utility of the Q-switched Nd:YAG was not realized until the late 1970s.
As described by Gloor, Fankhauser and Aron-Rosa were independently experimenting with pulsed lasers in the late 1970s.29 In 1977, Van der Zypen and Fankhauser evaluated Q-switched Nd:YAG procedures on animals30 while Aron-Rosa was investigating a mode-locked version.29 Aron-Rosa published the first manuscript on Q-switched Nd:YAG applications in 1980,31 followed by Fankhauser, Roussel, and Steffen.32
The Nd:YAG laser was available in the American market33 in 1982 and quickly became the laser of choice for laser iridotomy,34 but its primary application was for posterior capsule opacification (PCO). The laser allowed for effective disruption of any posterior capsule opacities without entering the eye with instruments, which reduced the risk of endophthalmitis.35 The instant improvement in visual acuity demonstrated by Aron-Rosa31 in 1980 and Terry et al.36 occurred in over 90% of each of their studies with a relatively non-invasive and fast procedure laid the foundation for this laser to become a primary workhorse for PCO and LPI. Today, the Q-switched Nd:YAG is heavily used and is being investigated for vitreolysis, with a recent study demonstrating favorable outcomes.37
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