Refractive and topographic results after exchange of Intacs SK for Ferrara intrastromal corneal ring segments after unsuccessful implantation for keratoconus correction

In the past, the main goal of intrastromal corneal ring segment (ICRS) implantation was to reduce keratometry. Current treatment nomograms based on classifi cation of the ectasia phenotype aim to provide both therapeutic and refractive correction. We present the case of a 39-year-old woman diagnosed in 2011 with keratoconus in both eyes, with low best spectacle-corrected distance visual acuity (BCVA) (3/10 Snellen decimal) in the left eye and contact lens intolerance. After surgical implantation of two symmetric 300 μm Intacs SK ICRS (Addition Technology, USA) based on the Amsler-Krumeich classifi cation, BCVA was 2/10 despite a reduction in mean and maximum keratometry; topographic astigmatism and vertical coma (Z3 -1) remained unchanged. Two years later, both Intacs SK ICRS were removed and a single Ferrara ICRS with 150° arc length and 200 μm thick segment was implanted. One year later, BCVA improved to 8/10, with signifi cant reduction in both corneal astigmatism and vertical coma. In patients unsuccessfully treated with ICRS, explantation or exchange for a Ferrara type-ICRS based on the ectasia phenotype was found to be safe and eff ective. J Emmetropia 2016; 3: 159-165 Keratoconus is an ectatic corneal disorder in which progressive thinning causes the cornea to become conical, resulting in irregular astigmatism and decreased visual acuity (VA)1,2. Options for managing keratoconus include spectacles2, rigid gas-permeable or soft contact lenses3,4, intrastromal corneal ring segments (ICRS)5-9, corneal collagen crosslinking (CXL)10-13, and keratoplasty12,14,15. In cases of contact lens intolerance and low spectacle-corrected distance visual acuity (BCVA), ICRS implantation is a safe and eff ective procedure for correction of irregular astigmatism and higher order aberrations, namely the vertical coma aberration, improving the uncorrected and corrected distance visual acuity (CDVA)8,9. Th e Ferrara-type ICRS is currently the most frequently used type of ICRS, essentially because it has a wider range of optical zones, arc lengths and thickness profi les, which allows a larger number of possible combinations for implantation. However, most studies on ICRS outcomes report variable numbers of patients in whom the surgical procedure is ineff ective or even responsible for a loss of CDVA16-19. Besides surgical complications, loss of BCVA after ICRS implantation has been attributed to incorrect choice of nomogram for the procedure. Most nomograms available in the past used the grade of ectasia rather than the phenotype to choose the correct number, arc length and thickness of the ICRS to implant. Besides the irregular corneal astigmatism, the presence of corneal high order aberrations20-23, namely the vertical coma (Z3 −1), greatly impacts the level and quality of vision of patients with keratoconus. In order to achieve a satisfactory visual and refractive outcome with ICRS implantation, the ICRS nomogram has to take into account both the irregular astigmatism and corneal high order aberrations. Th ere are currently two types of ICRS models available for implantation: Intacs and Intacs SK (Addition Technology, USA), and Ferrara ICRS (AJL, Spain). Th e standard Intacs have a hexagonal cross-section, are available in 11 sizes (from 210 μm to 450 μm) and have the same arc length of 150 degrees; the optical zone of implantation is 7.0 mm. Intacs SK is a new ICRS design with a smaller 6.0 mm optical zone to correct higher grades of ectasia and an elliptical cross-section to minimize the glare usually associated with smaller optical zones. Th e acronym “SK” denotes severe keratoconus or steep keratometry. Th e Ferrara ICRS has a triangular crosssection that induces a prismatic eff ect on the cornea. Submitted: 1/23/2016 Revised: 4/21/2016 Accepted: 5/5/2016 1 Hospital de Braga. Braga, Portugal. 2 Escola de Ciências da Saúde da Universidade do Minho. Braga, Portugal. Financial Disclosure: None of the authors has a fi nancial or proprietary interest in any product, material or method mentioned herein Corresponding Author: Tiago Pacheco Teixeira Monteiro Rua Dr. Alberto de Macedo, 295. 4100-031, Porto, Portugal E-mail: [email protected]