LASIK for correction of hyperopia and hyperopia with astigmatism

Correction of hyperopia with or without astigmatism by laser-assisted in situ keratomileusis (LASIK) has proved far more challenging than the correction of myopia. Unlike laser treatment of myopia, LASIK leaves the central cornea untouched. The excimer treatment, through the rotation of hemimasks, is applied to the midperiphery to steepen the central cornea. The system typically performs a peripheral ablation of 8.0 to 8.50 mm and a transition zone of 1 to 2 mm, which varies depending on the magnitude of the hyperopia. The optical zone is a parabolic zone of 5.5 to 6.5 mm. In this chapter, the largest prospective study of LASIK treatment in patients with hyperopia with or without astigmatism (326 eyes of 178 patients) is presented by Drs. Suarez and Torres, whose patients were part of a larger series. In the entire series, there were 1,929 eyes of 1,037 patients with myopia, myopia with astigmatism, hyperopia, hyperopia with astigmatism, and simple astigmatism, who underwent LASIK between February 1995 and February 1996 and whose data were analyzed statistically. Keratomileusis was developed by Barraquer [1] as a means of modifying the anterior corneal curvature for the correction of ametropia. Further development of the technique by others resulted in a wider adoption of the procedure in the form of automated lamellar keratoplasty (ALK) [2, 3]. This procedure is very effective, but its predictability is poor and modifications for the correction of astigmatism have not gained popularity. Trokel and colleagues [4] described the use of the 193-nm argon-fluoride excimer laser in 1983 for corneal ablations as a way to modify corneal curvature. Subsequent improvements in the laser delivery systems led to the superficial photorefractive keratectomy (PRK) procedure for myopia and astigmatism. However, this method destroys Bowman's layer in the zone of treatment. The importance of preserving Bowman's layer may be demonstrated by the high rate of anterior corneal haze formation after PRM procedures [5] and by the conspicuous absence of this haze after keratomileusis, despite its routine use in the treatment of high myopia. Such observations led some investigators to combine the two techniques and develop LASIK [6-9].