Introduction
The surgical reduction of hyperopia is an evasive but worthy pursuit since hyperopia affects both distance vision 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).
See related CME at Highlights of the American Society of Cataract and Refractive Surgery Symposium.
History of the Procedure
The technique routinely used for hyperopic LASIK uses a 110- to 160-µm 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 Media file 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 patient with hyperopia.
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 Media file 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 enhanced patient fixation and centration in the following ways:
- Transparent lenses on the patient's corneal stroma allowed visualization of the fixation light.
- The green tint of the lenses maximized the unimpeded passage of the green fixation light into the patient's eye, helping the patient to visualize and fixate on this light in maintaining consistent centration.
- Patients with hyperopia have a difficult time visualizing the fixation light due to their farsightedness. Incorporating a spherical power of +2.5 D into these lenses dramatically improved their ability to clearly visualize and fixate.
All of the above features helped to improve patient fixation and to decrease anxiety, enabling a well-centered hyperopic corneal sculpting with consistent results.
Technology innovations and advances, chiefly in the field of laser technologies, flying spot applications, iris recognition, wavefront analysis, and custom ablations, will eventually pan out into a more dependable approach with laser vision surgery for hyperopia.
Problem
Hyperopia generally is due to a shorter axial length or reduced corneal dioptric strength.
Frequency
Various figures are given, but, generally, it is believed that hyperopia affects millions of individuals in the United States.
Etiology
Hyperopia may run in families.
Presentation
A primary finding is a reduction of vision. Near or distance vision can be affected depending on age and refractive error. With proper correction, the vision is good.
Indications
In this study, LASIK was used to treat 4 different groups of hyperopia, as follows:
- Hyperopia with astigmatism of less than 0.75 D
- Hyperopia with astigmatism of greater than 0.75 D
- Overcorrected radial keratotomy
- Overcorrected automated lamellar keratoplasty
This article is limited to a discussion of LASIK for virgin eyes with hyperopia of less than 6.00 D and coexisting astigmatism of less than 0.75 D and the impact of the new intra-ablative lenses on the same eyes.
Relevant Anatomy
With hyperopia, the axial length is generally shorter or the corneal dioptric strength is weaker.
Contraindications
Contraindications for LASIK include lupus erythematous and rheumatoid arthritis.
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Further Reading
Keywords
hyperopic LASIK, hyperopia, farsightedness, laser refractive surgery, distance vision, excimer laser, laser in situ keratomileusis
