Influence of corneal cross-linking on visual acuity and topometric indices in keratoconus

CORRESPONDING AUTHOR Magdalena Maleszka-Kurpiel, MD, Department of Optometry, Chair of Ophthalmology and Optometry, Poznan University of Medical Sciences, 5D Rokietnicka St., 60-806 Poznan, Poland, e-mail: m.maleszka-kurpiel@optegra.com. pl INTRODUCTION Keratoconus (KC) is defined as a chronic, bilateral, noninflammatory corneal disorder characterized by progressive steepening, thinning and scarring of the cornea [1]. The application of novel technologies extends this definition to abnormalities in posterior corneal elevation, corneal thickness distribution and corneal epithelium thickness profile [2, 3]. Keratoconus usually starts at puberty and progresses until the third or fourth decade of life [1]. The prevalence of KC varies widely between published studies. The lowest (0.0003%) was reported in Russia [4]. In other studies values from 0.086% in Denmark and 0.249% in Iran up to 2.3% in India were reported [5-7]. The highest prevalence, reported by Torres et al. in a pediatric population in Saudi Arabia, is 4.79% [8]. There are no current data available concerning the KC prevalence in Poland. Despite numerous genetic and environmental factors which were identified as causing KC, the etiology and mechanism of progression of this ectasia remain unclear and are still under study. In 2018 in the review publication by Loukovitis et al. 24 genes were described as involved in KC etiology [9]. Further investigations include examination of DNA methylation changes in keratoconic eyes [10]. Environmental factors include intensive eye rubbing. It has to be emphasized that eye rubbing is a cause of significant increase of levels of matrix metalloproteinase (MMP)-13, interleukin (IL)-6 and tumor necrosis factor α (TNF-α) in tears of healthy volunteers [11]. It is well correlated with other studies in which levels of IL-6, TNF-α, and MMP-9 are increased in tears of patients with KC [12]. Patients with keratoconus reported more frequent and intense eye rubbing during contact lens use compared to non-keratoconic contact lens (CL) users [13]. Moreover, rigid gas permeable contact lenses (RGP) use increases levels of proinflammatory cytokines and cell adhesion molecules in eyes with KC [14]. Contact lenses play an important role in visual rehabilitation but do not inhibit KC progression [2]. The most important KC-preventive measures include: instructing the patient about the harmful effects of rubbing the ABSTRACT Aim of the study: To assess the impact of corneal cross-linking (CXL) in keratoconic eyes on uncorrected (UCVA) and best corrected (BCVA) distance visual acuity, selected corneal parameters measured with a Scheimpflug imaging system, intraocular pressure (IOP) and endothelial cell density (ECD). Material and methods: 71 eyes of 61 patients treated with CXL were included in the study. Each patient underwent optometric and ophthalmological examination with corneal tomography. Data from the qualifying visit and 1-year post-surgery examination were analyzed. Results: Comparative analysis of the pre-operative and 1-year post-operative evaluation showed improvement in median UCVA of –0.1 (logMAR) and median BCVA of –0.06 (logMAR). Manifest spherical equivalent showed a median change of almost 0.4 D and the power of the manifest cylinder did not change. The regression in the anterior keratometry steep meridian was greater than in the flat meridian, –0.9 D and –0.6 D respectively. The median Kmax change value was –1.2 D. Topometric indices analysis showed improvement in corneal symmetry. We did not observe changes in IOP and ECD. Conclusions: CXL is a safe procedure, improving visual acuity, both uncorrected and corrected, and normalizing corneal parameters.