Conductive keratoplasty (CK) is a type of non-invasive refractive surgery that uses heat from radio waves to reduce the collagen surrounding the cornea in the eye to improve presbyopia, a condition wherein the eye has trouble simultaneously focusing on objects at different ranges due to aging, and hyperopia, also known as farsightedness. Keratoplasty refers to the transplant or grafting of the cornea. The cornea is a clear, lustrous dome that covers the iris and pupil at the front of the eye and provides most of the refraction and focusing power of the eye. Refraction is the bending of light as it passes through a medium, which shortens the focal length in the eye, allowing the eye to focus more easily.
The cornea is about a half millimeter (0.0197 in.) in width and composed of five layers. In order from anterior to posterior, the layers are epithelium, Bowman's membrane, stroma, Descemet's membrane and the endothelium. Conductive keratoplasty is concerned with the peripheral area of the stroma, a clear, tough, fibrous layer composed of parallel fibrils of collagen.
During conductive keratoplasty, the eye surgeon will topically anesthetize the eye and then insert a speculum to hold the eye open. The surgeon will then use a thin tipped, pen-like instrument to draw small circles around the cornea with radio waves, or radiofrequency (RF) energy. This energy creates a mild heat that shrinks the peripheral corneal collagen into a tight band. This reshapes the curvature of the cornea, making it a steeper angle. The new curvature allows light to be bent more drastically as it enters the eye so that the patient can focus at a shorter distance.
Patients with hyperopia, presbyopia, or both suffer from negative changes in the curvature, and thus the refractive power, of the cornea. In farsighted patients, this usually has to do with the eyeball being too short or the lens not being round enough, causing an inability to focus on near objects. In patients with presbyopia, aging causes a loss of elasticity and hardening in the lens and degradation of the curvature muscles, which in turn causes a decrease in refractive power. This usually occurs in patients in their forties. Conductive keratoplasty is not a good option for those with myopia, or nearsightedness, but it has shown to work well for patients with hyperopia and presbyopia.
The Food and Drug Administration (FDA) approved conductive keratoplasty for use in 2002; first only for patients over forty with farsightedness, and later for patients with presbyopia. Unlike hyperopic patients, CK patients with presbyopia only have one eye treated and leave the dominant eye untreated. The untreated eye may then focus on greater distances, while the treated eye can focus on objects at close range. For this reason, conductive keratoplasty is often preferred to glasses or contact lenses because it is less likely to impair distance vision. The procedure for presbyopia may not be the best option for all patients, so doctors will often examine the patient beforehand with single lenses over the non-dominant eye to test if vision remains clear at distances.