History of Refractive Surgery
Forerunners to Modern Refractive Surgery
The study of visual problems (refractive errors) began in the early sixteenth century when Leonardo da Vinci contemplated the possible source of visual disturbances. A little later, in 1619, Scheiner measured the anterior surface of the cornea. His discoveries are still used by ophthalmologists today who recognize that refractive surgery often depends on changing the cornea's anterior contour. Even lens removal as a means of correcting high degrees of myopia was discussed by Boerhaave in 1746. But real progress in the field of vision correction was constrained until a better understanding of how the eye functions was acquired.
Johannes E. Purkinje observed in 1823 that images form on optical surfaces when they reflect external light. His observations led to the development of the Purkinje principles and the four Purkinje images. From these developments our modern-day understanding of keratometry (measuring the curvature of the cornea) and theories of visual accommodation began to grow.
Several decades later came the advent of topical (eye drop) anesthesia, which led to cataract surgery after the Civil War. In 1867, with the development of the keratometer (an instrument for measuring the curvature of the cornea), surgeons could measure astigmatism following cataract surgery.
In 1869 Snellen (after whom the vision charts of today are named) proposed using incisions across the steep meridian of the cornea to flatten it and treat astigmatism. However, twenty-one years would pass before anyone (Galezowski) would actually attempt (albeit unsuccessfully) to flatten the corneal contour.
Trials and Experimentation
Not long after a successful cataract surgery technique was developed by van Graefe in the 1850s, ophthalmologists everywhere began to recognize the impact of corneal shape on astigmatism. In 1895 Faber performed a full thickness corneal incision to decrease naturally occurring astigmatism in a nineteen-year-old patient, thus enabling him to pass his vision test for entrance into the Royal Military Academy. But all of these efforts were focused on astigmatism; no one looked beyond astigmatism to myopia or hyperopia. It soon became apparent that a better understanding of the principles of keratotomy (the making of incisions in the cornea) was needed before any further progress could be made.
It was about this time that a Dutch physician, Leendert Jan Lans (working at the time on his doctoral degree), began to systematically study and define the principles of keratotomy. So fundamental and comprehensive was his research that it soon became the standard of refractive surgery. He practiced and promoted the principles of corneal flattening that could be achieved by incisions made on the anterior surface of the cornea. By varying the number, direction, and shape of the incisions, Lans could manipulate the effects and tailor the visual correction.
In addition to surgical techniques, there were nonsurgical attempts at reducing myopia by manipulating the shape of the eye. One remedy was an eye cup with a spring-powered mallet designed to flatten the cornea; another was a firm rubber band used to flatten it. But these were techniques that failed to result in any significant degree of visual correction.
With the exception of the work performed by Lans, 1885 to 1939 was principally a time of trial and error for refractive surgery. Nevertheless, the successes and failures of this period helped determine which refractive procedures worked and which did not.
Modern Refractive Surgery
In 1936 Tsutomu Sato observed a flattening of the cornea in patients who had sustained traumatic injury to the eyes. The corneas of these patients were irregular and abnormally steep (keratoconus) but flattened after episodes of corneal swelling. His work led numerous assistants to establish the value of radial keratotomy, built upon the principles outlined by Lans nearly half a century earlier and applied to the treatment of keratoconus corneas. Sato brought anterior and posterior keratotomy to clinical practice in hundreds of patients and reported his results in the early 1940s. Other ophthalmic surgeons subsequently used his technique and obtained similar results.
Sato also applied his posterior keratotomy technique to the correction of astigmatism; this technique involved the disruption of the corneal endothelium, the internal cells of the cornea. Unfortunately, the role of the corneal endothelium in maintaining corneal thickness and clarity was not fully understood in Sato's time, and the subsequent development of corneal swelling in the majority of his patients who received this treatment went undetected until after his death.
In 1948 Ridley, a physician to Royal Air Force pilots in World War II, noted that pilots whose eyes harbored slivers of Perspex (cockpit "glass") seemed to have little or no reaction to this foreign material. This led him to suppose that a small lens made out of the same material could probably be tolerated inside the human eye. Soon he began experimenting with plastic lens designs, and the modern era of intraocular lens implantation for cataract surgery was born.
About the same time that Ridley envisioned the plastic intraocular implant, José Barraquer in Columbia developed the idea of lamellar (pancake and flap based) corneal surgery to alter the shape of the cornea. He discovered that lamellar keratoplasty could flatten the cone of a keratoconus patient, significantly reducing myopia.
In 1949 Barraquer described the principles of lamellar surgery. He changed the cornea's shape by removing the anterior cornea (the equivalent of today's corneal flap) with an instrument called a microkeratome, freezing it, and changing its shape with a mechanical lathe called the cryolathe. In the mid-1980s the cryolathe rose to its highest state of precision through automation. In 1985 Casimir Swinger developed a method of changing the shape of the cornea without freezing it. He did this using the microkeratome only. Then in 1987 Luis Ruiz, a protégé of Barraquer, modified the principles of microkeratome corneal resection by using an automated form of the instrument to perform the operation directly on the eye. This procedure, called automated lamellar keratoplasty (ALK), was used to correct high levels of myopia and hyperopia.
Halfway around the globe, a handful of Russian ophthalmologists began research to determine whether or not RK (radial keratotomy, or straight-line incisions placed in a spoke-like pattern around the periphery of the cornea) could be effective if it was confined to the anterior side of the cornea. This would thereby avoid the long-term problems that arose from the disruption of the corneal endothelium in Sato's posterior keratotomies.
By the mid-1970s, Russian scientists such as Durney, Yenaleyev, and Fyodorov had determined that most of the radial keratotomy flattening effect could be obtained with sixteen or fewer incisions placed only on the anterior cornea. Fyodorov developed a system of anterior radial keratotomy that, by varying the number of incisions and the amount of uncut clear central zones between them, permitted him to carefully control the degree of visual correction. It was he who convinced the world that radial keratotomy (RK) could indeed reduce or eliminate myopia.
Radial keratotomy was introduced into the United States in 1978 by Leo Bores. It soon became a subject of great interest and careful scientific scrutiny. In 1980 the National Institutes of Health sponsored the PERK (Prospective Evaluation of Radial Keratotomy) study which provided factual, scientific data on radial keratotomy performed in a standard manner in nine centers across the United States.
The Arrival of the Excimer Laser
The first step in the evolution of laser surgery occurred when experts researched the application of laser technology to vision correction. In 1980 Beckman and Peyman and their associates used a carbon dioxide laser to create thermal shrinkage of the cornea in order to change corneal contour. A year later in 1981 John Taboada reported at a meeting of the Aerospace Medical Association that the argon-fluoride excimer laser had the ability to indent eye tissue. Work then proceeded on ablation (microsurgical removal) of corneal tissue to flatten the cornea. Further evaluation was performed by Steve Trokel.
The first use of the excimer laser on blind human eyes took place in 1985 by Seiler in Germany. This was followed in 1987 by L'Esperance of the United States. The procedure was called photorefractive keratectomy (PRK) and involved the ablation of the surface of the cornea to flatten its central portion in order to correct nearsightedness. In 1989 Michelson and four other American ophthalmologists traveled to the Free University of Berlin to observe Seiler perform photorefractive keratectomy on patients who were nearsighted. In 1991 Michelson and this elite group of ophthalmologists became the first five clinical investigators of the excimer laser in the United States, utilizing the laser manufactured by Summit Technology.
By 1990 and 1991, Pallikaris and Buratto and their associates had combined lamellar splitting (using the blade of a microkeratome to make a corneal flap, based on Barraquer's pioneering work forty years earlier) with excimer laser ablation of the exposed corneal bed. It was Pallikaris who coined the term LASIK (laser in-situ keratomileusis). This procedure took the moderately successful automated lamellar keratoplasty (ALK) procedure and added the incredible accuracy of the excimer laser to improve the results.
The LASIK procedure avoids the anterior stromal haze and pain generally associated with surface ablation by the excimer laser (PRK). This result is achieved because the laser is applied only within the corneal substance rather than removing a large area of epithelium (the thin, outer surface layer of the eye). When the epithelium is removed during PRK, the nerve endings are exposed; these exposed nerve endings cause pain during recovery. Additionally, there are more fibroblasts underneath the epithelium, and these contribute to scarring. Lastly, the epithelium is the eye's mechanical barrier to bacteria; removing it increases the risk of keratitis (infection). With LASIK, the epithelium remains almost entirely intact. As a result, the nerve endings stay covered and there is minimal pain during recovery. With the epithelium intact and healed within twelve hours after the procedure, there is a lower risk of infection and scarring.
The initial clinical trials of LASIK in the United States began in 1996, and Michelson was again one of the first LASIK surgeons involved. These clinical investigations culminated in the approval by the FDA of the LASIK procedure in 1999.
With LASIK, the realm of refractive surgery has given wings to the space-age dream of a relatively quick, virtually pain free, refractive correction procedure, one that is now taking off.
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