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    Wavefront-guided PRK after CXL for keratoconus

    Alexandria, Egypt—Wavefront-guided photorefractive keratectomy (WFG PRK) performed using a proprietary high-definition aberrometer (iDesign, Abbott Medical Optics) and excimer laser system (VISX STAR S4 IR, Abbott Medical Optics) appears to be a safe and effective option for improving vision in eyes with keratoconus that achieve stability after corneal collagen crosslinking (CXL), according to the experience of Mohamed Shafik, MD, PhD.

    Results from analyses of data collected in a consecutive series of 34 eyes of 25 patients followed for up to 12 months post-WFG PRK were reported in a paper published online in Cornea on May 17, 2016. The outcomes show statistically significant improvements in uncorrected and corrected distance visual acuity (UCDVA and CDVA) corresponding to statistically significant reductions in mean manifest sphere and cylinder. Statistically significant improvements were also achieved in some topographic corneal irregularity indices and in higher order aberrations (HOA), including total HOA, primary coma, and trefoil.

    Related: What you should know about SMILE and wavefront guided LASIK

    No eyes lost CDVA or developed significant haze—the surgical protocol included mitomycin-C 0.02% applied to the ablated tissue for 20 seconds—and there was no evidence of keratoconus progression after WFG PRK.

    Dr Shafik noted that the high-definition aberrometer has made WFG PRK feasible in eyes with keratoconus because the device can capture an accurate wavefront in highly aberrated corneas and thereby allows a reliable ablation profile. And, he told Ophthalmology Times Europe that he considers the WGF ablation superior to a topography-guided approach for this indication. In addition, he believes that there is an advantage for performing surface ablation sequentially rather than simultaneously with CXL. Now, further studies are needed to validate the theories underlying these ideas, said Dr Shafik, Professor of Ophthalmology, University of Alexandria, and medical director, Horus Vision Center, Alexandria, Egypt.

    “Excimer laser surgery to correct the refractive error in eyes with keratoconus treated by CXL has been controversial because of concerns that it would further compromise biomechanical stability. However, surface ablation has less effect on corneal biomechanics than LASIK, and the eyes in my series have maintained good stability so far,” he stated.

    More keratoconus: Keratoconic eye experience with a long-arc intrastromal corneal ring

    “In addition, the functional and refractive outcomes achieved with WFG PRK in eyes with keratoconus stabilised by CXL compare favourably with those reported in the literature for topography-guided PRK performed in combination with CXL or as a second procedure. Nevertheless, longer follow-up in more eyes is needed to confirm the safety of WFG PRK after CXL and comparative studies are needed to evaluate outcomes using different ablation protocols.”

    All eyes in the consecutive series had grade I or II keratoconus (Amsler-Krumeich classification) and had undergone CXL at least 1 year earlier. In addition, they had to meet the following criteria: <0.5 D variation on subjective refraction at three consecutive monthly visits; <0.75 D increase in the cone apex keratometry in the previous 6 months; manifest spherical equivalent refraction ≤6 D; logMAR CDVA 0.5 or better; clear cornea within the pupillary area; and thinnest pachymetry ≥400 microns. Presence of dry eye syndrome or history of herpetic eye disease, autoimmune disease, or active anterior and posterior segment pathologies are considered contraindications to performing WFG PRK after CXL.

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