3 Femtosecond Laser-Assisted In Situ Keratomileusis (LASIK)

Ioannis G. Pallikaris and Onurcan Sahin

Keywords: history, femtosecond LASIK, excimer, photorefractive keratectomy, laser, keratome

3.1 History of LASIK

Surgical correction of refractive errors on the human eye has been a big challenge since the introduction of refractive keratoplasty by Barraquer. ¹ Since then, development of every new technology helped scientists and surgeons to understand the deficiency of the current procedures and motivate them to create new and better technique and technologies. Although several advanced procedures were created, new procedure-related complications occurred. The requirements to overcome those existing and new complications motivated refractive surgery to evolve from the early 1950s to today.

Development of excimer (excited dimers of inert gases) laser opened a new and wide area in the refractive surgery on the cornea, although Houtermans had described the bound-free excimer in 1960. ² The discussion of excimer lasers goes back to 1938. ³ The first commercial excimer laser (1976) was used in several application areas such as micro-machining or material processing. ^{4,​ 5} The use of excimer lasers on tissue was first suggested by Ruderman in 1979. ⁴ The first use of excimer lasers in ophthalmology was in radial keratotomy (RK) by Trokel and Srinivasan. Excimer lasers were used to make precise radial cuts in the cornea instead of using diamond or steel blades. The applications were performed on eyes of albino rabbits and monkeys. After these animal trials, the Food and Drug Administration (FDA) approved the first human trial for a 193-nm argon fluoride (ArF) excimer laser application. ^{6,​ 7,​ 8,​ 9} The first refractive corneal surgery was performed and published by Trokel et al in 1983. ^{6,​ 10} Findings of the trials and comparative studies ⁸ showed that the use of excimer lasers could offer better outcomes while avoiding most other serious complications. ¹¹

3.1.1 Photorefractive Keratectomy

Advancement of using the excimer laser technology created an alternative technique for refractive surgery. The concept was modifying the refractive properties of the central cornea by removal of superficial stromal tissues using an excimer laser. This application was called photorefractive keratectomy (PRK) and first applied by Seiler et al in 1988. ¹² Several studies were enrolled for determining the efficacy, predictability, and safety of PRK. ^{10,​ 12,​ 13,​ 14,​ 15} U.S. FDA approved Summit Technology for excimer laser PRK in 1995. ¹⁶

There were several advantages of PRK over RK. PRK was a minimally invasive technique and offered high precision in the surgery, which was simple for the surgeons and the patients. PRK could create a smooth corneal surface and the photochemical process could be controlled to incise tissue to a precise depth and with submicron accuracy. ⁸ The thermal, ¹⁷ mechanical, ¹⁸ and actinic ¹⁹ damage to the adjacent tissue was negligible. ²⁰

Further studies on postoperative results of PRK revealed several complications such as corneal haze, regression, delayed visual rehabilitation, unpredictability (higher than 6 D), and halos related to the PRK surgeries. ^{11,​ 12,​ 20,​ 21,​ 22,​ 23,​ 24,​ 25}

3.1.2 LASIK

In order to overcome the complications of PRK surgery, Pallikaris et al developed a new surgical technique, which is called “laser in situ keratomileusis” (LASIK). Creation of a corneal flap was aimed with lamellar dissection by a specially designed microkeratome. The first trials were performed on albino rabbits in order to demonstrate the proof of concept. The aim of the procedure was to maintain the integrity of anterior corneal layers and to overcome complications of the PRK surgery. The first results were promising and were published in 1990. ²⁶

The first clinical studies were performed on blind human eyes by Pallikaris et al. In order to create the 300 µm corneal flap the BKS 1000 (Barraquer-Krumeich-Swinger) microkeratome with specially designed suction ring (Polytech, Darmstadt, Germany) was used. After excimer laser application (ArF 193 nm), a soft contact lens was applied (no use of suture or bioadhesives). The early postoperative results were promising and findings were published in 1991. ²⁷

The first three FDA approved systems for LASIK surgeries are the Kremer Excimer Laser System (Lasersight Technologies, Inc.), SVS Apex Plus Excimer Laser Workstation (Summit Technology, Inc), and VISX Excimer Laser System Model C “Star” (AMO Manufacturing USA, LLC). ^{28,​ 29,​ 30}

Fast rehabilitation, no postoperative pain, earlier postoperative stabilization of visual acuity, and less corneal haze were the revealed advantages of LASIK compared to PRK. ^{31,​ 32,​ 33,​ 34,​ 35,​ 36} LASIK was considered as the more advanced procedure. The requirement of additional advanced equipment, a longer surgery time, being not applicable for thin corneas, and patients with preoperative dry eye syndrome were considered as disadvantages of LASIK compared to PRK.

Although the overall results of LASIK were indicating a success, several important intra- and postoperative complications were reported. The majority of intraoperative complications related to the microkeratomes. These complications included incomplete passes, thin flaps, buttonholes, and free flaps. ³³ Perforation of the anterior chamber was also reported. ³² Dry eye syndrome, flap-induced aberrations, ^{33,​ 34,​ 36,​ 37,​ 38} and most importantly corneal ectasia ^{39,​ 40,​ 41} were postoperative complications of LASIK.

The risk of ectasia and flap-induced aberrations created the demand of an improvement of the LASIK technique. Even though the advanced surface ablation (Epi-Lasik, ^{42,​ 43,​ 44,​ 45} LASEK, ^{46,​ 47,​ 48} PRK MMC ^{49,​ 50,​ 51}) were suggested, the results of these applications pushed the demand of the thin-flap LASIK applications. Thus, more advanced microkeratomes were developed in order to create a thinner, predictable, and reproducible flap.

3.1.3 Femtosecond LASIK

Juhasz in collaboration with Kurtz and Kruger worked on ultrafast lasers (picosecond and femtosecond) for creating corneal flaps for the LASIK surgery. In the late 1990s, first studies in animal and human eyes were published. ^{52,​ 53,​ 54,​ 55,​ 56,​ 57,​ 58,​ 59,​ 60} The first FDA-approved femtosecond laser for refractive surgery was the Intralase in 2000. ⁶¹

The use of femtosecond laser–assisted excimer laser surgeries created significant advantages to the prior technologies. ^{54,​ 62,​ 63,​ 64,​ 65,​ 66,​ 67,​ 68}

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