August 08, 2012
3 min read

Higher-order aberrations decrease with corneal collagen cross-linking

Study finds improvement in anterior corneal and ocular higher-order aberrations, particularly coma.

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Corneal collagen cross-linking decreased higher-order aberrations in patients with keratoconus or corneal ectasia after LASIK, suggesting an improvement in the cornea’s optical architecture, according to a study.

The prospective, randomized study used topographic and wavefront analysis to measure corneal higher-order aberrations and total ocular aberrations in 96 eyes of 73 patients with keratoconus (64 eyes) or post-LASIK ectasia (32 eyes) who underwent corneal collagen cross-linking (CXL).

A control group comprised 42 untreated fellow eyes of patients who did not receive bilateral CXL.

Visual acuity was measured preoperatively and at 1-year follow-up. A questionnaire was administered asking study participants to rate visual symptoms such as night vision, glare, halo and starbursts.

The study was published in the Journal of Cataract and Refractive Surgery.

Higher-order aberrations

“We found on average that higher-order aberrations were improved,” senior study author Peter S. Hersh, MD, FACS, OSN Refractive Surgery Board Member, said.

Peter S. Hersh, MD, FACS 

Peter S. Hersh

In contrast, higher-order aberrations worsened in the control group.

“CXL not only stabilizes this progressive disease, but also improves some of the quantitative optical indicators of the disease as well,” Hersh said.

Study patients treated with CXL achieved corneal topography stabilization and minimal progression. The mean total anterior corneal higher-order aberrations significantly decreased from 4.68 µm preoperatively to 4.27 µm at 1 year (P < .001). Mean anterior corneal total coma decreased from 4.40 µm to 4.01 µm, third-order coma decreased from 4.36 µm to 3.96 µm, and vertical coma decreased from 4.04 µm to 3.66 µm (all P < .001).

Significant decreases were also observed in total ocular higher-order aberrations (from a mean preoperative 2.8 µm to 2.59 µm at 1 year), total coma (2.60 µm to 2.42 µm), third-order coma (2.57 µm to 2.39 µm), trefoil (0.98 µm to 0.88 µm) and spherical aberration (0.90 µm to 0.83 µm).

“The improvement in coma, which is the most particular aberration for keratoconus and ectasia, demonstrates directly that by using CXL we are generally influencing for the better the optical problems that these patients encounter,” Hersh said. “There were no significant changes in posterior corneal higher-order aberrations, suggesting that CXL primarily affects the anterior cornea.”

Improvement in corneal topography from preop to 1 year after CXL may lead to improvement in corneal and total ocular aberrations. 

Improvement in corneal topography from preop to 1 year after CXL may lead to improvement in corneal and total ocular aberrations.

Source: Hersh PS

Visual acuity and symptoms

The study also found that visual acuity and a number of topographic characteristics improved significantly. Overall, CXL patients achieved approximately one line of improvement in both corrected and uncorrected visual acuity.

Patient-reported visual symptoms improved as well.

“Although there was only a small average improvement in starbursts after CXL, there was a significant correlation between total ocular aberrations and individual patient’s improvement,” Hersh said.

The mean preoperative rating for the presence of starbursts was 2.6 on a scale from 1 (none) to 5 (severe). At l year it decreased to 2.5.

“Although other symptoms improved as well, we were unable to show a statistical correlation with decrease in aberrations,” Hersh said. “This may be a result of the large variation in visual symptoms and objective metrics in keratoconus and ectasia patients.”

Hersh and colleagues are conducting a follow-up study targeting patients’ subjective visual function before and after CXL.

CXL has yet to be approved by the U.S. Food and Drug Administration, but preliminary results have been promising, he said.

“I think the results we have seen worldwide are very encouraging for treatment,” Hersh said. “The data we have had in the U.S. is quite good for safety and efficacy. We are hopeful for FDA approval.” – by Bob Kronemyer

  • Greenstein SA, Fry KL, Hersh MJ, Hersh PS. Higher-order aberrations after corneal collagen crosslinking for keratoconus and corneal ectasia. J Cataract Refract Surg. 2012;38(2):292-302.
  • Hersh PS, Greenstein SA, Fry KL. Corneal collagen crosslinking for keratoconus and corneal ectasia: one-year results. J Cataract Refract Surg. 2011;37(1):149-160.
For more information:
  • Peter S. Hersh, MD, FACS, can be reached at 300 Frank W. Burr Blvd., Suite 71, Teaneck, NJ 07666; 201-883-0505; email:
  • Disclosure: Hersh is the paid medical monitor for Avedro.