Slight Posterior Corneal Protrusion After LASIK and PRK

Lara C. Pullen, PhD

January 27, 2015

Femtosecond laser-assisted LASIK and photorefractive keratectomy (PRK) are both associated with mild but statistically significant forward protrusion of the posterior cornea. According to results from a new study, the forward protrusion fluctuated for a year in patients who received LASIK, but stabilized as early as 3 months after patients received PRK. A similar pattern was seen even after the researchers made adjustments for differences in the preoperative and postoperative parameters between the two treatment groups.

Tommy C.Y. Chen, FRCS, from the Chinese University of Hong Kong in China, and colleagues present the results of their corneal imaging study in an article published online December 5, 2014, in Ophthalmology. The investigators used swept-source optical coherence tomography to measure 98 eyes from 49 patients (mean age, 35.2 ± 8.5 years) at months 1, 3, 6, and 12 postsurgery.

Swept-source optical coherence tomography measures and computes corneal topography directly from the posterior corneal surface. The investigators found, at 1 month, a mean change in posterior elevation of 4.88 ± 0.47 μm in eyes that received LASIK and a mean change in posterior elevation of 3.67 ± 0.48 μm in eyes that received PRK. The LASIK and PRK eyes showed a significant difference at months 3 and 12 (P ≤ .023).

The results suggest that swept-source optical coherence tomography may be useful for measuring the posterior cornea after refractive surgery.

Although the investigators identified a difference in corneal topography, the clinical implications of such a measurement remain unclear. "In our study, although the difference between posterior corneal elevations in both groups was statistically significant, we did not note any clinical significance for this difference at up to 1 year of follow-up. Long-term follow-up studies may help to highlight any differences between LASIK and PRK," they write.

There have been conflicting reports about the ability of slit-scanning topography and Scheimpflug photography to accurately measure posterior corneal surface. Many of the previous studies have focused on microkeratome-assisted LASIK. The use of swept-source optical coherence tomography and femtosecond-assisted LASIK likely accounted for the measurable outcome in this study.

The measured change was notably small, however. "It is such a small change that you have to wonder if this instrument is accurate enough to measure such a small change," emphasized Steven E. Wilson, MD, from the Cleveland Clinic in Ohio, in an interview with Medscape Medical News.

Dr Wilson acknowledged that the change in measurement could be real, but he also hypothesized that it might be the result of cloudiness in the cornea postsurgery.

The authors and have disclosed no relevant financial relationships.

Ophthalmology. Published online December 5, 2014. Abstract

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