Laser Thermal Keratoplasty (LTK)

What is the objective of an LTK procedure?
How is the LTK procedure performed?

Laser thermal keratoplasty (LTK) is a refractive surgery procedure that uses a Holmium laser to reshape the cornea for correction of low ranges of hyperopia (farsightedness). The Holmium laser is an infrared (thermal) laser that uses heat to shrink corneal tissue.

On the other hand, the Excimer laser uses a cool beam to vaporize corneal tissue. The Excimer laser is used in the laser in-situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) procedures.

In LTK, the Holmium laser is used to gently heat stromal collagen in a ring around the outside of the pupil. The heat causes the tissue to shrink, thereby creating an effect like tightening a belt. The periphery of the cornea is pulled, causing the center to bulge. Because the cornea of a farsighted eye is too flat, this bulging effect, when carefully controlled, corrects the problem.

People with mild hyperopia, +0.75 to +2.75, are prime candidates for LTK. It is also being used to treat presbyopia (age-related loss of focus) and overcorrection from radial keratotomy (RK), PRK, and LASIK procedures. LTK is currently under investigation by the FDA for approval in the United States, and patients can only be treated as part of the investigational protocol.

What is the objective of an LTK procedure?

To understand how LTK works, it is first necessary to understand the visual function of the eye. The eye works like a camera with two lenses. The first lens is the cornea, a clear membrane that covers the front of the eye. The second lens is the eye's natural crystalline lens, which is located behind the pupil. The cornea is responsible for about 70 percent of the eye's focusing power, while the natural lens fine-tunes the image before it is focused on the retina, at the back of the eye. The retina works like the film in a camera, receiving light images and sending them through the optic nerve to the brain (See Anatomy of the Eye.). If both lenses are working properly, the image is focused precisely on the surface of the retina and the result is perfect 20/20 vision.

Just as people are born with different sizes and shapes of hands, their eyes also vary in form and proportion. A perfect eye has an evenly rounded cornea that allows light to fall exactly on the retina resulting in perfect vision. If the cornea is too flat or the eye is too short from front to back, light rays are theoretically focused behind the retina, resulting in hyperopia (farsightedness). The objective of LTK is to make the cornea steeper in order to correct for farsightedness.

How is the LTK procedure performed?

The LTK procedure is performed on an outpatient basis with topical anesthetic eyedrops to numb the eye. Based on the patient's prescription, the laser's computer is calculated to deliver the number of pulses and the diameters of the circles needed to provide the proper amount of correction. After aligning the pupil with the use of a slit-lamp microscope, the surgeon activates the laser, and it transmits tiny beams of infrared light in two concentric rings around the periphery of the cornea. Because moisture in the cornea absorbs the energy in the laser pulses, the tissue shrinks slightly creating tiny craters, which tighten the cornea and result in a steeper surface. The laser never touches the eye, and the entire process takes just a few seconds per eye.

The LTK procedure is painless, although the patient may have blurry vision and a mild scratchy sensation for a couple days. Antibiotic eye drops are normally used for about a week, and, if needed, Tylenol and ice packs can be used to relieve discomfort. Most eyes are fully healed in three days, and, although many patients report almost instant vision improvement, vision stabilization usually occurs within two weeks.