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Chapter 20 – LASIK: Indications and Techniques

Chapter 20 – LASIK: Indications and Techniques

JOHN F. DOANE
STEPHEN G. SLADE

DEFINITION
• LASIK stands for laser in situ keratomileusis, in which an anterior flap of cornea is lifted with a keratome and an excimer laser is used to sculpt the stromal bed to change the refractive error of the eye.

KEY FEATURES
• LASIK is the most commonly used corneal refractive procedure.
• It can be used to treat wide ranges of refractive error.
• Laser sculpting can be used to treat near- and farsightedness and astigmatism.
• It can be used in conjunction with other refractive techniques for extremely large ametropia.
• In the near future, LASIK may be used to provide improved lines of acuity postoperatively.

ASSOCIATED FEATURES
• As in other corneal refractive surgeries, LASIK complications can result in a loss of best spectacle-corrected vision.
• Most complications can be managed to preserve vision.
• LASIK continues to evolve with improvements in technology and understanding.

INTRODUCTION
Refractive lamellar corneal surgery has been used to correct myopia and hyperopia for more than 40 years, and for the majority of that time, it has been performed by relatively few centers. [1] [2] [3] [4] [5] Conceptually, refractive lamellar corneal surgery attempts to remove, add, or modify the corneal stroma so that the radius of curvature of the tear film–anterior corneal interface is altered as desired. Laser in situ keratomileusis (LASIK) has gained increasing popularity since 1995. Benefits of lamellar refractive surgery include:
• Ability to treat a large range of refractive error effectively.
• Relatively short visual rehabilitation period postoperatively.
• Relatively pain-free experience for patients.
• Less intense healing response, compared with other modalities. [6] [7] [8] [9] [10] [11]
Disadvantages of lamellar surgery include the risk of serious side effects, a large capital outlay, and the technical expertise required to perform an acceptable lamellar keratectomy. Clinical outcomes of efficacy, predictability, safety, and stability for lamellar refractive surgery are available from numerous sources. [12] [13] [14] [15] [16]
HISTORICAL REVIEW
Corneal lamellar refractive keratoplasty has its roots in the work of Professor Jose Ignacio Barraquer, beginning in 1949 in Bogota, Colombia. [1] [3] [4] [5] Barraquer developed myopic keratomileusis,

Figure 20-1 Lamellar dissection using a microkeratome. The corneal flap is created by applanation of the cornea, which is carved in a similar fashion to using a carpenter’s plane.
which used a cryolathe to shape the cornea and alter its refractive power. The term keratomileusis is derived from the Greek roots keras (“horn-like,” referring to the cornea) and smileusis (“carving”).[2] The main difficulties with myopic keratomileusis were the training and experience required to perform the keratectomy effectively and the complexity of managing the cryolathe. When a manual keratome is driven across the eye by hand, the thickness and evenness of the keratectomy are intimately dependent on the speed of the passage ( Fig. 20-1 ). Any irregularity in this cut results in irregular astigmatism for the patient and a subsequent decrease in best-corrected vision.[2] [12] [13] [14] [15] [16] Complications specific to myopic keratomileusis and lamellar keratoplasty include epithelial ingrowth in the stromal interface and induction of irregular astigmatism. [2] [12] [13] [14] [15] [16] Good results were obtained initially by several investigators; however, the technique proved too difficult to master for a large number of surgeons.[13] [14]
The concept that the corneal cap can be raised and central tissue removed from the bed, keratomileusis in situ, was first described by Krwawicz[17] in 1964 and subsequently by Pureskin[18] in 1967. Dr. Luis Antonio Ruiz, in Bogota, developed a microkeratome with gears that advanced the instrument across a geared track with an adjustable-height suction ring; this system made the automated lamellar keratoplasty (ALK) technique possible. This motorized advancement of the microkeratome allowed a constant-velocity passage that resulted in the resection of a lamellar disc of tissue of even thickness and a smoother corneal stromal bed. This substantial instrumentation breakthrough

174
made lamellar corneal surgery more appealing to a larger number of surgeons.
Several reports that revealed relatively poor predictability, central haze, and regression with photorefractive keratectomy (PRK) for moderate myopia (-3 to -6D) and even more so for high myopia (>-6D), [6] [7] [8] [9] [10] [11] [19] [20] [21] [22] [23] [24] [25] along with the relatively wide predictability range and safety concerns for myopic ALK and keratomileusis in situ,[26] [27] prompted researchers to substitute lasers for the keratome in the refractive correction step of the myopic ALK procedure. [28] [29] [30] [31] [32] [33] [34] [35] [36]

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