History of Refractive Surgery
Forerunners to Modern Refractive Surgery
The study of visual problems and 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 shape of 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 lens accommodation began to grow.
Several decades later, the advent of topical (eye drop) anesthesia led to less painful 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, two decades would pass before Bates in New York would successfully flatten the corneal contour with incisions.
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 and corneal heating. 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. His work formed the historical basis of modern refractive keratotomy and thermal keratoplasty.
In addition to surgical techniques, there were nonsurgical attempts at reducing myopia by manipulating the shape of the eye. One novel remedy was an eye cup with a spring-powered mallet designed to pound the cornea flat through a closed eyelid; another was a firm rubber band used to flatten it. But these techniques failed to produce any significant degree of visual correction.
With the exception of the work performed by Lans, Bates, and some Italian collegues, 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 1939 in Tokyo, Japan, Tsutomu Sato observed a flattening of the cornea in patients who had a peculiar corneal disease. The corneas of these patients were irregular and abnormally steep (keratoconus) but flattened after episodes of spontaneous corneal swelling. His work led to numerous animal and human studies of radial keratotomy, built upon the principles outlined by Lans nearly half a century earlier and applied to the treatment of keratoconus corneas. Sato and his colleagues brought anterior and posterior keratotomy to clinical practice in hundreds of patients and reported his results in the 1940s and 1950s.
Sato also applied his posterior keratotomy technique to the correction of astigmatism; this technique of posterior corneal incision caused disruption of the corneal endothelium, the internal cells of the cornea. Unfortunately, the role of the corneal endothelium in maintaining corneal clarity was not fully understood in Sato's time, and the subsequent development of corneal swelling in many of his patients who received this treatment went undetected until after his death. Nevertheless, Sato's work was the basis for the development of modern radial keratotomy.
In 1948 Harold Ridley, a physician to British 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 Bogota, Columbia, developed the idea of lamellar (layered) 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 a disc of the anterior portion of the cornea (the equivalent of today's corneal flap) with an instrument called a microkeratome, freezing the disc, and grinding it into a new 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 in New York, Casimir Swinger developed a method of changing the shape of the cornea without freezing it (nonfreeze keratomileusis). 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 Durnyev, 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 control the amount of visual correction. It was he who popularized radial keratotomy (RK) for the reduction or elimination of myopia.
Leo Bores introduced radial keratotomy into the United States in 1978. 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. The principal investigation of this study (based at Emory University in Atlanta, Georgia) involved nine different eye centers around the country, lasted fifteen years, and cost over $20 million. It produced the first factual, scientific data on radial keratotomy and set refractive surgery in general on a solid clinical base. At the same time many researchers, such as Richard Lindstrom in Minneapolis, refined the hundred-year-old technique of transverse keratotomy for astigmatism--a single, effective treatment still in use today.
The Arrival of the Excimer Laser
The first step in the evolution of laser eye 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 John Taboada reported at a meeting of the Aerospace Medical Association that the argon-fluoride excimer laser had the ability to indent surface epithelial corneal tissue.
It was Steve Trokel, an acknowledged expert in laser eye treatments, and Srinivasan, a Ph.D. researcher who discovered the principle by which an excimer laser removes substances and tissues (photoablative decomposition), who combined their knowledge and proposed applying the excimer laser to reshaping corneal tissue. First, they tried the laser for radial keratotomy (unsuccessful). Later, in conjunction with John Marshall in London, they devised the idea of sculpting the cornea into a new shape by ablating tissue in a controlled pattern.
The first use of the excimer laser on blind human eyes took place in 1985 by Theo 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.
Numerous American ophthalmic surgeons, such as Margaurite McDonald and Sard Herbert Kaufman of New Orleans, began to investigate and refine PRK in conjunction with European colleagues, leading to the first U.S. Food and Drug Administration (FDA) approval of the Summit brand excimer laser in 1995.
PRK became popular around the world but had two nagging problems: (1) Patients' eyes were sore for forty-eight hours and had blurry vision for almost a week after surgery because PRK left the corneal surface raw and exposed. (2) The process required to heal this raw area produced corneal haze, and in rare cases scars blurred the vision and altered the accuracy of the treatment.
Surgeons subsequently conceived of ways to avoid these problems by returning to time-honored keratomileusis (layered carving), which left the corneal surface smooth immediately after surgery. In the late 1980s, Luccio Burroto in Italy used the excimer laser instead of the cryolathe to reshape the back of the remniel corneal disc. Ionnos Pallikaris used the laser to reshape the corneal bed, modifying the inaccurate ALK technique and giving rise to the modern, accurate, LASIK procedure. The LASIK acronym refers to "LASer" (meaning excimer laser), "In situ" (meaning in place in the corneal bed under the flap), and "Keratomileusis" (meaning to carve the cornea).
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 tissue rather than removing a large area of epithelium (the thin, sensitive, 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. The epithelium also forms the smooth optical surface of the cornea required for sharp vision, so when it is removed, vision becomes blurry until the epithelium heals.
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, there is minimal pain during recovery, and sharper vision returns in twenty-four to forty-eight hours. 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 by Stephen Slade and Stephen Brint. A broad series of clinical investigations culminated in the approval by the FDA of the LASIK eye surgery procedure in 1999.
With LASIK eye surgery, the realm of refractive surgery has given wings to the space-age dream of a relatively quick, virtually pain free, highly accurate, refractive correction procedure, one that is now taking off. But, as with most of medical science, research continues and results improve, refining laser vision correction. Microtreatments are becoming more refined. Excimer lasers are becoming more sophisticated, refractive surgeons are becoming more skilled, and methods of measuring vision and the eyes are expanding.
A goal of laser eye surgery is to allow you to be less dependent on glasses or contact lenses or eliminate them completely. Most individuals can see 20/20 with optical correction; this is average "best corrected" vision. But the normal eye is capable of seeing better than 20/20: 20/16, 20/12, 20/10, and rarely, 20/05.
The goal of LASIK surgeons around the world is to refine refractive surgery techniques in general, and laser eye surgery in particular, to allow patients to experience significantly improved quality, as well as quantity of vision by correcting not only the lower order aberrations, causing nearsightedness, farsightedness and astigmatism but also higher order aberrations that cause dissatisfaction with glasses and contact lenses. This will be accomplished, in part, by using newly developed clinical instrumentation that will allow us to measure these aberrations and then by designing a custom laser eye surgery treatment for each individual eye. This will be further discussed in Chapter Eleven.