The first significant clinical ophthalmic application of any laser system on human subjects was the treatment of retinal tears with a pulsed ruby laser.
The term “laser” is an acronym for light amplification by stimulated emission of radiation. Substances have the property to “laser,” that is, to absorb energy in one form (either thermal, mechanical, electrical, or light—all ophthalmic lasers use light as the stimulating source) and to emit a new form of light energy that is more useful. The utility of laser light is caused by a number of its unique properties.
Particularly useful is the concentration or brightness of the light. In fact, a laser produces the brightest light source known to humans. The development of the laser for ophthalmic use arose from the initial concentration of conventional light by magnifying lenses.
A substance that has the ability to lase possesses the unique property of transferring electrons from one orbital to a second orbital of higher energy. The theory of Niels Bohr
The light then oscillates back and forth within the laser cavity (usually a tube with a mirror at each end, one mirror being highly reflective and the other mirror allowing some laser light to pass through for use in the eye). The laser light that passes through the partially reflective mirror may be altered in several ways to make it more effective for ophthalmic use, one of which is to concentrate further the laser light into a small interval of higher intensity.
Theodore Harold Maiman, formerly a research scientist at Hughes Aircraft Research Laboratories, was one of the few scientists interested in the use of solid materials—namely, ruby crystals—as a laser material. On July 7, 1960, Maiman made public his discovery of the first laser—a ruby laser. Shortly thereafter, ophthalmologists began using ruby lasers for medical purposes.
The first significant medical (ophthalmic) uses of the ruby laser occurred in 1961, with experiments on animals conducted by Charles J. Campbell, H. Christian Zweng, and Milton M. Zaret. Zaret and his colleagues produced photocoagulation of the eyes of rabbits by flashes from a ruby laser. Sufficient energy was delivered to cause instantaneous thermal injury to the retina and iris of the pigmented rabbit. The beam also was directed to the interior of the rabbit eye, resulting in retinal coagulations. The researchers examined the retinal lesions and pointed out both the possible advantages of laser as a tool for therapeutic photocoagulation and the potential applications in medical research.
In 1962, Zweng, along with several of his associates, began experimenting with laser photocoagulation on the eyes of monkeys and rabbits to establish parameters for the use of lasers on the human eye. (In their later experiments with humans, all patients were treated with the experimental laser photocoagulator without anesthesia.) Although usually no attempt was made to seal holes or tears, the diseased portions of the retina were walled off satisfactorily so that no detachments occurred. When attempts to obliterate microaneurysms were unsuccessful, the researchers postulated that the color of the ruby pulse so resembled the red of blood that the light was reflected rather than absorbed. They believed that another lasing material emitting light in another part of the spectrum might have performed more successfully.
Campbell and his colleagues began experimenting on human subjects (in addition to animals) in August of 1963. Their clinical trials on adult pigmented rabbits, using both the laser and the xenon arc photocoagulator, indicated that, qualitatively, the lesions produced by these two instruments appeared to be similar, but the laser coagulations were located at a relatively more external level of the retina. Microscopic sections confirmed that the laser, with proper power controls, produced not destructive pathologic changes but therapeutic coagulations. They also produced therapeutic retinal burns in a series of human subjects and successfully treated retinal tears. In their research, they found that coagulations formed by the laser were smaller than those produced by the xenon arc and concluded that the laser was a desirable and feasible way of producing coagulations of the human retina.
Previously, xenon-arc lamp photocoagulators had been used to treat retinal tears, but the long exposure time of these systems (250-1,000 milliseconds, as opposed to the ruby laser’s 0.2-1.0 milliseconds), combined with their broad spectral range emission (versus the single wavelength output of a laser), made the retinal spot on which the xenon arc could be focused too large for many applications. Focused laser spots on the retina could be as small as 50 microns.
The vitreous body, which usually fills the vitreous cavity of the eyes of younger individuals, commonly shrinks with age, with myopia, or certain pathologic conditions, causing it to separate from the adjacent retina. In some patients, the separating vitreous produces a traction (pulling) on an area of vitreo-retinal adhesion, causing a retinal tear to form. Through this opening in the retina, liquefied vitreous can pass to a site underneath the retina, producing retinal detachment and visual loss. The purpose of photocoagulation of a retinal tear is to cause an adhesive scar to form between the retina surrounding the tear and the underlying layers so that, despite traction, the retina does not detach. If more than a small area of retina has detached, the laser often is ineffective and major retinal detachment surgery must be performed. Thus, in the experiments of Campbell and Zweng, the ruby laser was used to prevent, rather than treat, retinal detachment.
The first laser in ophthalmic use by Campbell, Zweng, and Zaret, among others, was a solid laser—Maiman’s ruby laser. While the results they achieved with this laser were more impressive than with the previously used xenon arc, in the decades following these experiments, argon gas replaced ruby as the most frequently used lasing material in treating retinal tears.
While the ruby laser was found to be highly effective in producing an adhesive scar, it was not useful in the treatment of vascular diseases of the eye. A series of laser sources, each with different characteristics, have been considered, investigated, and used clinically for various durations during the period that followed Campbell and Zweng’s experiments.
Subsequently developed lasers in the solid state include the YAG, a laser made of a synthetic crystal originally developed as a gemstone, yttrium aluminum garnet—abbreviated YAG. Other laser types that are being adapted for use in ophthalmology are carbon dioxide lasers for scleral (the tough, white, fibrous membrane covering the entire eyeball except the area covered by the cornea) surgery and eye wall resection, dye lasers for photodynamic inactivation of tumors, eximer lasers for their ability to break down corneal tissue through a photochemical nonthermal process that dissolves organic molecular bonds without tissue heating, and pulsed erbium lasers used to cut intraocular membranes.
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citation-type="booksimple" xlink:type="simple">Apfelberg, David B., ed. Evaluation and Installation of Surgical Laser Systems. New York: Springer-Verlag, 1987. This excellent work is intended to be a complete information source both for those relatively unfamiliar with the laser as well as for the experienced laser user. All details of laser biophysics, safety, and specialty uses are explained. In addition, the administrative, organizational, financial, and legal implications are outlined. Includes 103 illustrations and 33 appendixes, as well as a glossary of terms. -
citation-type="booksimple" xlink:type="simple">Ball, Kay. Lasers: The Perioperative Challenge. St. Louis, Mo.: C. V. Mosby, 1990. This well-written book provides an extensive overview of past and present advances in laser technology and use. It can be used as a fundamental reference tool for general knowledge as well as specialized knowledge in the field. Contains color plates, a glossary of terms, and suggested readings at the end of each chapter. -
citation-type="booksimple" xlink:type="simple">Goldman, Leon, and R. James Rockwell. Lasers in Medicine. New York: Gordon & Breach, 1971. This thorough and very informative work reviews the extensive and detailed work of a group of investigators who have been responsible for much of the developmental research in laser medicine and biology. The authors provide a general overview of the history and physics of laser emission, characteristics and measurement of laser radiation, laser biology, safety, as well as applications in ophthalmology, dermatology, and cancer research. Includes many graphs, charts, and illustrations. -
citation-type="booksimple" xlink:type="simple">Hering, Peter, Jan Peter Lay, and Sandra Stry, eds. Laser in Environmental and Life Sciences: Modern Analytical Methods. New York: Springer, 2004. Wide-ranging study of laser applications in medicine, biology, and environmental chemistry. Bibliographic references and index. -
citation-type="booksimple" xlink:type="simple">McGuff, Paul E. Surgical Applications of Laser. Springfield, Ill.: Charles C Thomas, 1966. The general scope of this brief and somewhat dated work is laser surgery, with special reference to the application of laser in the treatment of malignancy and, specifically, malignant tumors. Studies the effects of laser energy on human malignant tumors and formulates concepts and hypothesis derived from experimental studies. Glossary of laser terms, bibliography. -
citation-type="booksimple" xlink:type="simple">Waynant, Ronald W., ed. Lasers in Medicine. Boca Raton, Fla.: CRC Press, 2002. Collection of essays providing an overview of the history of medical laser applications. Bibliographic references and index. -
citation-type="booksimple" xlink:type="simple">Wolbarsht, M. L., ed. Laser Applications in Medicine and Biology. Vol. 2. New York: Plenun Press, 1974. This lengthy and detailed investigation of the rapid advances in laser technology gives an insightful view into the use of lasers in areas such as ophthalmology, holography, surgery, and dentistry. The work also discusses the issue of protective standards for the patient and the operator. Contains numerous graphs, charts, and illustrations.
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