A Study Of The Changes In Corneal Parameters In Patients With Keratoconus After Femtosecond Assisted Intra Corneal Stromal Rings Implantation.

Abstract

Keratoconus is an ectatic corneal disorder characterized by a progressive corneal thinning that results in corneal protrusion. These corneal changes result in a mild to severe decrease in the best-corrected visual acuity (BCVA) as a result of progressive myopia, regular and irregular astigmatism, and apical scarring. Most patients can be managed successfully with spectacles or contact lenses, especially in the early stages and with mild forms of the disease. However, when these measures fail to provide adequate vision or patients can no longer tolerate contact lenses, penetrating keratoplasty is an acceptable surgical alternative with high success rates but potential complications. Intracorneal ring segments (ICRSs) were first designed to correct myopia and astigmatism. It is now possible to use this method to decrease the curvature and irregularity of the cornea in patients with keratoconus. Intra-corneal ring segments act by exerting an ‘‘arc-shortening effect’’ on the corneal lamellae that flattens the central cornea. This procedure is safe and reversible No corneal tissue is removed, and the central cornea is not invaded. There are 3 available types of ICRSs depending on their curvature, width and zone of implantation: Intacs, Ferrara rings and Kerarings. Kerarings are characterized by triangular cross sections that induce a prismatic effect on the cornea when the flat posterior surface is inserted facing the corneal endothelium. The optical zone provided by the segments is 5.0 mm in diameter. Tunnel creation for segment implantation can be performed mechanically or through the femtosecond laser. The femtosecond laser has reduced or eliminated the surgical complications of mechanical implantation such as anterior chamber perforation, corneal thinning, corneal infiltration, microbial keratitits, and stromal edema, because it can create an accurate and uniform 360° depth. Our study was a prospective study, included 20 eyes of 18 patients who had been diagnosed with keratoconus according to standard criteria based on slit-lamp observation and corneal topography. We evaluated the changes in un-aided visual acuity and best-corrected visual acuity (UAVA & BCVA), spherical equivalent (SE), and topographic changes of the cornea before and3months after Kerarings implantation in keratoconic eyes using the femtosecond laser technique. In type I and type II keratoconus we used only one ring segment while in type 3 we used two intra-corneal ring segments. Inclusion criteria were: intolerance to rigid gas permeable contact lenses, clear central cornea, pachymetry of thinnest location was not less than 400 microns, and steepest keratometry readings (K readings) did not exceed 60 Diopters. Exclusion criteria were: presence of corneal opacities or vogt stria, pachymetry of thinnest location was less than 400 microns, steepest keratometry readings did not exceed 60 Diopters, and systemic collagen diseases. Kerarings implantation resulted in improvement in UCVA, BCVA, spherical equivalent (SE), and all keratometry readings (K1, K2, and Kmax). Also, we found a significant reduction in corneal topographic astigmatism with large effect size. Another index was the Q value which represents the asphericity of the anterior surface of the cornea also improved significantly. It can be considered as one of the markers of visual quality. We observed also the flattening effect exerted by Kerarings in the form of reduction of anterior floatwhich was statistically significant compared to the reduction of posterior float which was insignificant but with a medium effect size. In conclusion, Kerarings implantation using the femto-laser technique seems to be a minimally invasive treatment with good visual and refractive outcomes. Further larger, comparative studies focusing on the differences between manual traditional dissection and femtosecond laser dissection, and nomogram modification are needed. Also, comparing the outcome of using Keraring segments with other ICRS segments such as INTACs or Ferrara segments.Longer follow up periods are needed to document any possible complications of the technique.