Wavefront-guided PRK improves vision in eyes previously treated with radial keratotomy
Radial keratotomy (RK) is a non-laser refractive surgery procedure for the correction of myopia that was popular in the 1980s and early 1990s, before the introduction of laser procedures such as PRK and LASIK.
Though RK frequently provided good results, complications were common. These complications included:
- Regression of myopia (a return of nearsightedness over time)
- Overcorrections (causing a nearsighted eye to become farsighted)
- Significant increases in higher-order aberrations (causing glare and halos)
- Irregular astigmatism not correctable with eyeglasses or soft contact lenses
- Sensitivity to light
Fixing post-RK vision problems with PRK
People with vision problems after RK pose a significant challenge to refractive surgeons. Because RK involved making deep, radially arranged cuts in the cornea to flatten its shape (and thereby correct myopia), the post-RK eye is left with multiple scars.
These RK scars can increase the risk of serious flap complications if LASIK is attempted on post-RK eyes. For this reason, many laser surgeons prefer to perform the flap-free photorefractive keratectomy (PRK) procedure instead of LASIK on these eyes.
PRK after RK — Study design
Recently, researchers from The Wilmer Eye Institute (Baltimore, MD) investigated the refractive outcomes of wavefront-guided PRK in patients who had previously undergone radial keratotomy for the correction of myopia.
The study was a retrospective review of nine consecutive cases of PRK after RK that were performed between August 2004 and February 2007. In all cases, a VISX STAR S4 excimer laser (Abbott Medical Optics, Santa Ana, CA) was used for the wavefront-guided PRK procedure.
Prior to PRK, five of the post-RK eyes were hyperopic (ranging from +1.28 D to +3.12 D) and four were myopic (ranging from -0.80 D to -3.36 D). Six of the nine eyes had astigmatism, ranging from +0.50 D to +2.25 D.
The results of follow-up exams performed three months and one year after surgery were reviewed and visual acuity, residual refractive error and biomicroscopy findings were noted.
PRK after RK — Study results
Data from the follow-up visits after PRK revealed:
- Three months after surgery, seven of the nine eyes (77 percent) were within 0.25 D of the targeted spherical equivalent refraction. (The spherical equivalent is the average of the refractive result of the steepest and flattest meridian of an eye with corneal astigmatism.)
- All eyes with astigmatism prior to surgery had a significant reduction of astigmatic error after PRK, with the highest amount of residual astigmatism being 0.75 D in one eye and 0.50 D in two eyes.
- No eye lost any degree of best spectacle-corrected visual acuity (BSCVA) and three eyes (33 percent) gained one line of BSCVA.
- Only two eyes (22 percent) showed minor corneal haze after PRK, and this haze was not in the visual axis (within the central zone of the cornea where it might affect vision).
Conclusions
The researchers concluded that wavefront-guided PRK for the treatment of residual refractive error and higher-order aberrations after radial keratotomy is predictable, safe and effective.
SOURCE: "Wavefront-guided photorefractive keratectomy after radial keratotomy in nine eyes." Journal of Refractive Surgery. May 2009.
Last updated: February 2010
