Keratomileusis and Automated Lamellar Keratoplasty

Stephen U. Stechschulte

John F. Doane

The concept of lamellar refractive corneal surgery, or keratomileusis, originated with J. I. Barraquer (1,2) in 1949. Using a manual keratome (Fig. 73-1) he created a thin, free cap of corneal tissue that could be reshaped to alter its curvature and refraction. The cap was frozen and the underside was lathed to predictably flatten the curvature before replacing the cap on the stromal bed (Fig. 73-2). In Barraquer’s (3) hands, results of keratomileusis with a cryolathe were encouraging; however, the technique was complex and the equipment was costly to maintain.

A consistent and accurate manual free cap keratectomy is dependent on the speed at which the keratome passes over the eye. Moving too quickly results in an uneven and thin cap, whereas too slow of a pass creates an abnormally thick flap. Corneal cap irregularities can translate into irregular astigmatism and loss of acuity (4). Similarly, any irregularity in the lathing process can result in irregular astigmatism and loss of best corrected visual acuity. Additionally, the cryolathe was a very difficult instrument to maintain and master. The lack of consistent results with the manual keratome coupled with the complexities of the cryolathe led to a decline in popularity of keratomileusis and stalled its widespread adoption.

Although keratomileusis as conceived by Barraquer never gained popularity, his vision inspired the continuing evolution of lamellar refractive surgery. Krawawicz (5) and Pureskin (6) described a central stromal keratectomy, keratomileusis in situ, where tissue was removed from the corneal bed after a free cap had been created. Ruiz, working in Bogota, developed a microkeratome with gears that automatically advanced the microkeratome across a gearedtrack. This automation and the adjustable height suction ring made an automated lamellar keratoplasty technique possible. The motorized advancement of the microkeratome at a constant velocity created a predictably thick corneal cap, a predictable depth lamellar keratectomy, and a smoother corneal stromal bed. This instrumentation breakthrough made lamellar corneal surgery appealing to a larger number of surgeons.

SURGICAL TECHNIQUE: AUTOMATED LAMELLAR KERATOPLASTY FOR MYOPIA (ALK-M)

Automated lamellar keratoplasty (ALK) is done in an outpatient setting under topical anesthesia. As with all refractive surgery, extensive patient education and counseling is required. The patient must have an adequate knowledge of the procedure and its risks, and realistic expectations. Oral sedation may be used but is not mandatory. Prior to prepping and draping the patient the conjunctival cul-de-sacs are irrigated to remove debris and eyelid glandular secretions. It is important during the draping to create a clear path for microkeratome passage. The patient is instructed to look at the microscope light and an inked marker is used to delineate the optical center, a pararadial line for orientation of the flap and a 9-mm optical zone circle to center the circular suction ring. A spacer device, or depth plate, is placed in the microkeratome to determine the thickness of the cut. The first keratectomy in the current ALK technique is typically suggested to have a 160-μm depth plate. An adjustable suction ring is placed on the eye and engaged. The suction ring fixates the globe, provides a geared path for the microkeratome, and raises the intraocular pressure so that a smooth keratectomy may be obtained. A stopper device is often used to ensure the creation of a hinge in the corneal flap. Just prior to passage of the microkeratome the intraocular pressure is checked to make certain it is greater than 65 mm Hg with a hand-held Barraquer tonometer or a pneumotonometer. After the first cut, which has a planned diameter of 7.5 to 8 mm, the suction ring is removed. The adjustable suction ring is reset to resect a 4.2-mm-diameter piece of stromal tissue. A second depth plate is placed, which corresponds to the planned myopic correction. The suction ring is then replaced and a
second cut is made after checking the diameter and the intraocular pressure. The flap is then replaced and positioned, usually without sutures. The patient’s eye is not patched, and the patient is released from the clinic on antibiotic drops. The eye is examined the next day.