PRK, or photorefractive keratectomy, is safe for the correction of both low myopia and high amounts of nearsightedness, according to a long-term follow-up study of the procedure.
Researchers in Italy followed 31 patients who underwent either unilateral or bilateral PRK in 1991 to 1993. A total of 49 nearsighted eyes were included in the study, and check-ups were performed every two years over a period of 14 years.
Patients were divided into two groups — a “low myopia” group of subjects with less than -6.00 diopters (D) of myopia (range: -1.50 to -5.75 D) prior to surgery, and a “high myopia” group of subjects with at least -6.00 D of pre-operative myopia (range: -6.00 to -13.00 D).
PRK study: Results
Results at the final post-operative visit 14 years after surgery included the following:
Low myopia group:
- Mean residual refractive error was -0.17 D of myopia.
- Mean uncorrected visual acuity (UCVA) was between 20/20 and 20/25.
- Mean best spectacle-corrected visual acuity (BSCVA) was 20/20.
- 84 percent of subjects said they were satisfied with the results.
High myopia group:
- Mean residual refractive error was -0.67 D of myopia.
- Mean UCVA was nearly 20/25.
- Mean BSCVA was nearly 20/20.
- 75 percent of subjects said they were satisfied with the results.
In both groups, some degree of corneal haze increased three to six months after surgery, then declined over the subsequent six months.
Complications included minor corneal haze (two eyes), transient unequal pupil size (nine eyes), and iron-containing deposits in the corneal epithelium (four eyes).
No occurrences of ectasia or irregular astigmatism were noted, and no eyes had abnormal endothelial cell count or changes in endothelial cell shape (changes in the inner cell layer of the cornea that could lead to corneal clouding and vision loss). Three patients (9.7 percent) reported night vision problems.
Results achieved six months after surgery were maintained for up to 14 years with no evidence of regression of myopia in eyes in either group.
PRK study: Conclusions
The researchers concluded that PRK is a safe and effective procedure for the correction of myopia.
They noted, however, that results are less predictable for correction of high amounts of myopia.
Editor’s note: The PRK procedures in this study were performed with laser technology and techniques used in 1991 to 1993. It is possible that patients undergoing PRK with today’s modern laser technology may experience fewer night vision problems.
SOURCE: A 14-year follow-up of photorefractive keratectomy. Journal of Refractive Surgery. June 2009.
Tags: myopia, nearsighted