Refractive Surgery for Myopia, Myopic Astigmatism, and Mixed Astigmatism

Nicole J. Anderson, MD, Elizabeth A. Davis, MD, David R. Hardten, MD

Refractive surgical options for the treatment of myopia and myopic astigmatism include laser surgeries, incisional surgeries, intrastromal ring segments, phakic intraocular lenses, and refractive lensectomy. Bioptics, or a planned combination of more than one refractive surgical modality, is also gaining popularity. For mixed astigmatism, several techniques are being used, including astigmatic keratotomy, photorefractive keratectomy, and laser in situ keratomileusis.

Laser Surgery

Photorefractive Keratectomy

Photorefractive keratectomy (PRK) was developed in the late 1980s as the first laser vision correction procedure. In October 1995, PRK became the first FDA-approved laser treatment for the correction of myopia and myopic astigmatism.

In PRK, a surgeon uses a 193-nm argon fluoride excimer laser to resculpt the surface of the cornea to correct refractive errors. In this procedure, the epithelium is removed by one of several techniques, including

manual scraping
rotating brush removal
laser ablation followed by manual scraping (laser-scrape)
laser ablation (transepithelial)

Following the epithelial removal, the laser reticule is centered over the entrance pupil and the laser ablation is performed on Bowman's membrane. The cornea is irrigated with a balanced salt solution, and a bandage contact lens is left in place for 3–7 days, until the epithelium regenerates. Most surgeons treat one eye at a time because functional visual acuity does not return until the epithelium has healed.

Depending on the type of laser used, PRK is approved for the treatment of myopia up to -13.0 D and astigmatism up to -4.5 D. PRK is more predictable in patients with a lower degree of myopia (<6.0 D).^1-5 Patients with a higher degree of myopia who are treated with PRK tend to have more regression of their refractive effect^3,6 and more significant haze.^6-8

To minimize haze formation following PRK, surgeons prescribe the use of topical steroids for several months. In larger treatments, the use of antimetabolites to prevent haze formation may be beneficial. Preliminary rabbit and human studies suggest that a single intraoperative application of topical mitomycin C (0.2 mg/mL) may reduce corneal haze associated with PRK.^9,10 However, the long-term safety of antimetabolite use in refractive surgery has not been established.

Depending on the study and the amount of myopic correction, PRK has been successful in achieving uncorrected visual acuity of 20/40 or better in 67%–98% of patients, with 48%–81% of patients achieving 20/20 uncorrected visual acuity.^11-16 Long-term refractive outcomes of PRK and LASIK are similar.⁴⁶