Higher-order aberrations more severe after RK than PRK, study shows

ARHUS, Denmark — The image-forming properties of the cornea are better after photorefractive keratectomy than after radial keratotomy, a study here found. Higher-order aberrations were almost twice as high after radial keratotomy as after photorefractive keratectomy when measured at pupil sizes of 4 mm and 6 mm, the study found.

Researchers randomized 96 patients with myopia of between -0.75 D and –5 D to undergo either radial keratotomy (RK) or photorefractive keratectomy (PRK). At 1 year after surgery, wavefront aberrations and Zernike polynomial coefficients were calculated at pupil sizes of 2 mm, 4 mm and 6 mm.

The total corneal wavefront aberrations after RK and PRK were similar and not statistically different at 1 year postoperatively. Wavefront aberrations arising from astigmatism or defocus accounted for about 70% of the total wavefront errors at all pupil sizes in both groups. Spherical aberration and coma were slightly higher after PRK than after RK.

At the 4 mm pupil size, astigmatism caused the majority of aberrations. The researchers found the formation of aberrations due to defocus "most remarkable" when the pupil size was increased to 6 mm.

"Although aberrations caused by astigmatism, coma and higher-order aberrations each doubled when the pupil size increased from 4 mm to 6 mm, spherical aberration increased five to six times," they said.

The study is published in the January/February issue of Journal of Refractive Surgery.