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Intrastromal ring implantation in keratoconus: retrospective study of visual results, refraction, aberrometry and topographic indices

Poster Details

First Author: I.Martinez Soroa SPAIN

Co Author(s):    L. Bascaran Oteyza   N. Goñi Damborenea   A. Bidaguren Urbieta   T. Alberdi Ibarloza   J. Mendicute  

Abstract Details


Retrospectively to analyze the changes in visual acuity, refraction, corneal topography and aberrometry following implantation of corneal intrastromal rings (ICRS) of 5 mm in diameter in patients with keratoconus with a postoperative follow-up of 6 months.


Donostia University Hospital, San Sebastian (Spain) .


Patients with keratoconus grade I-III (Krumeich-Amsler classification) underwent ICRS with manual technique or femtosecond laser. Pre-and postoperative uncorrected (UDVA) and corrected (CDVA) visual acuity and subjective refraction (sphere (Sph , cylinder (Cyl) and spherical equivalent (SE)) data were recorded. The topographic analysis was performed with the CSO Eye Top 6.4. Simulated keratometry (Kmin , Kmax , Kmed) and vector analysis with the Alpins method, average corneal power (ACP), apical keratometry (AK), gradient of corneal curvature (GCC ) (D/mm), inferior-superior asymmetry of the 3 mm central (IS ) and surface asymmetry index (SAI) were analyzed. Corneal aberrometry was studied on 5 mm centers from the conversion of corneal elevation map with Zernike expansion coefficients , analyzing the total corneal RMS (um), spherical aberration , coma, trefoil, spherical-like and astigmatism aberration as well as their vector analysis .


23 eyes of 20 patients were studied. UCVA improved from 1.04 to 0.52 and CDVA from 0.47 to 0.21 (p< 0.005) (logMAR). In the subjective refraction spherical equivalent diminished from -7.01 to -3.81 D (p< 0.005) . The Kmin decreased from 47.69 to 46.62 D (p: 0.051), the Kmax from 51.89 to 49.22 D and Kmed from 49.82 to 47.75 D (p< 0.005). ACP decreased from 50.39 to 48.90 D (p: 0.022), AK and GCC increased but showed no statistically significant difference. The topographic astigmatism decreased from 4.18 to 2.42 D (p: 0.019). The SI index decreased from 8.28 to 6.2 (p: 0.001) and the SAI from 5.13 to 4.03 (p: 0.008). Total RMS aberrometry corneal decreased from 3.30 to 2.82 microns (p: 0.013), come from 2.26 to 1.75 microns (p: 0.003) and astigmatic aberration from 1.68 to 1.29 microns (p: 0.038). The trefoil aberrations, spherical-like and spherical aberration showed no statistically significant difference. Preoperative and postoperative differences in the variables that caused major changes in visual acuity were studied, with the highest correlation between the difference in Kmin lines and improvement in UCVA (R: 0.450) and the difference in the Kmax and CDVA (R: 0.407).


ICRS implantation improved UCVA and CDVA, decreased subjective refraction and diminished topographic astigmatism significantly in keratoconus patients. . Topographic indices were significantly different reflecting decreased corneal flattening (Kmin, Kmax, Kmed and ACP) and irregular astigmatism (IS and SAI). Some topographic indices such as the AK and GCC showed worsening after ICRS and were evaluated as artifacts. The interpretation of the topography of Placido and its conversion to corneal aberrometry may be artifacted by the distortion of the view that cause the rings. Corneal aberrometry provided significant improvements in total aberration and higher order aberrations such as coma. The biggest changes in keratometry the greater improvement in visual acuity. FINANCIAL INTEREST: NONE

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