The History of Laser Eye Surgery

The excimer laser, used in laser eye surgery, was first developed in 1970, with its medical and industrial uses being explored throughout the 70's. The term excimer first emerged in 1960, to describe an energised molecule with two identical components. It was believed that the Argon molecule formed an excited dimer, and while this turned out to be untrue, the term persisted.

The excimer laser uses ultraviolet wavelengths between 193 – 351 nm.

The first experiments of ocular biological interactions of new lasers were performed by John Taboada for the United States Air Force in 1981. His work investigated the damage thresholds in rabbit eyes, and described an "indentation" of the corneal surface in the shape of a beam. Taboada's work intrigued Steve Trokel, who invited Taboada to contribute a book chaper on pulsed lasers. Trokel's curiosity also prompted him to seek access to an excimer laser himself.

Trokel saw the potential of the laser in improving radial keratotomy, particularly given the technical limitations of using a knife incision. Working in the IBM TJ Watson Lab, Trokel was interested in exploring the possibility of using direct laser keratomileusis to modify corneal optics. At the lab, Rangaswamy Srinivasan had been working with the laser for two years, and was the first to observe the effects of the laser on biological materials. Within weeks of Trokel's arrival, in June of 1983, experiments on veal eyes began.

In 1983, Trokel published a groundbreaking paper, reporting the essentials of excimer laser-cornea interaction, and sparking research efforts around the world as well as attempts at commercialisation. Trokel’s paper highlighted the accuracy of the laser, whereby each laser pulse removes a fraction of a micron of corneal tissue, the smooth, uniform surfaces created by the laser, the lack of collateral damage, the ability to control the shape and pattern of tissue removal, and the resulting clear corneas after use of the laser, despite not maintaining Bowman's membrane.

Building on Trokel's work, Charles Munnerlyn asked Trokel to try ablating specific shapes on the cornea. Based on these results, he worked out the mathematics, quantifying the relationship between tissue removal, optical zone size, and optical effect. For example, 5 µm tissue = 1D of reduction in refractive effect in 4-mm optical zone.

The resulting paper took Munnerlyn four years to finish, and was published in 1988. In it, the term "photorefractive keratotomy" (PRK) was coined, though it was initially deemed too speculative, and of no practical value.

As a result of his work, the "Munnerlyn equation" for estimating the ablation depth for a given treatment continues to be used today.

One of the major engineering challenges in the development of PRK was developing a device that could control the laser output appropriately. Munnerlyn convinced CooperVision to undertake this effort, and in 1985 they produced essentially the first working prototype.

In subsequent years, many researchers investigated 193-nm laser applications, looking at mostly peripheral incisional uses, but also therapeutic applications.

Researchers at the LSU Eye Centre continued studying PRK and phototherapeutic keratectomy (PTK) through out the 1980's. Trokel and Munnerlyn, along with Marguerite McDonald, a member of the Optical Express International Medical Advisory Board, conducted both animal and human eye research. Studying cadaver eyes, living rabbit and primate eyes, and eventually both blind and sighted humans, the first PRKs on blind, partially sighted and sighted eyes were performed from 1988 – 1990.

The research demonstrated the normal and clear healing of corneas, as well as the predictable refractive change that could be achieved using PRK technology. The pre-, intra-, and post-op clinical protocols were also established during this time, including the use of anaesthesia, suction, ablation procedure, and postoperative care.

Tremendous progress continued throughout the 1990s, including the development of optimal laser ablation patterns and refinement of algorithms, and better understanding of healing response.

Hyperopic corrections, astigmatic corrections, and LASIK, have also been made possible since the initial development of PRK, which continues to be performed today under the name of LASEK.

More recently, Wavefront technology has revolutionised optical science, while safer and clinically superior LASIK flaps are now being created using femtosecond technology.