Excerpt from Hyperopia, LASIK

Synonyms, Key Words, and Related Terms: hyperopic LASIK, farsightedness, laser refractive surgery, distance vision, excimer laser, laser in situ keratomileusis

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The surgical reduction of hyperopia is an evasive but worthy pursuit since hyperopia affects both distance and near vision and is compounded by presbyopia at a time when patients are in the prime of their vocational and personal life. A wide spectrum of refractive surgeries has been applied over the years in the relentless pursuit of hyperopia correction. With the introduction of the excimer laser, the possibilities of carving a positive lenticule into the cornea were investigated. To steepen an untreated corneal center, it is necessary to have a relatively deep peripheral ablation with a progressive steepening of the transition of zone 1.

The argon fluoride 193-nm excimer laser corrects refractive errors by sub–micron-precision tissue removal from the cornea. Photorefractive keratectomy (PRK) has been used successfully for hyperopia but has problems of regression, induced astigmatism, and corneal haze, thereby limiting its usefulness to the correction of mild hyperopia only. Excimer laser in situ keratomileusis (LASIK) overcomes many disadvantages of surface ablation (PRK) and has become the procedure of choice for treating hyperopia up to +6.00 diopters (D).

History of the Procedure: The technique routinely used for hyperopic LASIK uses a 160- to 180-mm thick corneal flap and a wide ablation with a peripheral blend zone. With different output systems and configurations unique to each excimer laser system, the conceptual ablation pattern results in a relative central steepening to correct the hyperopia.

When using a broad beam laser, the central cornea could be protected from the laser ablation, while the periphery would ablate resulting in central steepening. The author had been practicing this technique to correct low hyperopia with good results but was finding patient fixation and surgeon control to be an obstinate problem.

Surgical innovation in hyperopic LASIK - Design of masks

Three acrylate polymer masks of diameters 4.5 mm, 4 mm, and 3.5 mm, respectively, were designed and custom made by Gulani (see Image 1). The surface of the masks was spherical, convex for hyperopia correction. The edges were thinned out evenly to a smoothly polished finish. These masks were centered on the exposed corneal stroma between the laser beam and the eye, successively starting with the 4.5-mm mask, followed by the 4-mm mask, and, finally, the 3.5-mm mask, to allow the final ablation pattern to reveal a central graduated steepening comprised of 3 concentric rings. The lenses were transparent with a green tint to allow for maximum light penetration by the green fixation light on the laser. Each lens was +2.5 D in power to aid fixation by the hyperopic patient.

A specially designed triple zone marker and lens placement forceps (designed by Gulani) were used with these lenses during surgery. The principle behind designing these lenses stemmed from a desire to improve patient fixation and surgeon visibility of the ongoing procedure. Prior to the use of these masks, aluminum masks of the same base diameters, respectively, were used. Since these masks were not transparent, the patients could not see the fixation light and had a tendency to wander unless closely held by the globe fixator (designed by Gulani). Also, the surgeon could not see the corneal stroma under these masks; therefore, they had no active role to play in centration of the final concentric ring ablation pattern.

Making these lenses out of a transparent material helped both the surgeon and the patient and resulted in a well-controlled, supervised, and predictable hyperopic laser corneal sculpting (see Image 2). Now, the surgeon could center these lenses and maintain direct observation during laser ablation.

These lenses were modified further to incorporate a green tint, with each powered to +2.5 D. These factors further enha .....