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Prospective study analysing customised virtual ray tracing aberrometry and clinical results before and after implantation of different combinations of ICRS in keratoconus

Poster Details

First Author: N.Alejandre-Alba SPAIN

Co Author(s):    P. Perez-Merino   S. Marcos   I. Jimenez-Alfaro              

Abstract Details


Irregularity in keratoconus (KC) reduces best-corrected visual acuity (BCVA) and the visual Strehl ratio (VSR), which measures the optical quality of the cornea. Intracorneal ring segments (ICRS) aim to improve corneal regularity in order to avoid corneal transplant. Clinical algorithms to choose ICRS for each patient are diverse and there is a lack of data on the effect of each combination of segments. This study analyses corneal, aberrometric and refractive changes when ICRS are chosen to improve coma and astigmatism. It also tries to measure the usefulness of the VSR in order to judge the improvement after ICRS implantation.


Universitary Hospital Fundacion Jimenez-Diaz. Cornea Unit.


This is a prospective observational study including patients with keratoconus who underwent femtosecond laser ICRS insertion. The segment combination was chosen in taking into account the corneal shape of each patient. All patients underwent full ophthalmic examination before and after surgery. Corneal elevation points in each visit were obtained using Pentacam HR Scheimpflug camera. The corneal elevation data were fitted by Zernike polynomial expansion (up to sixth order) and exported to ZEMAX for virtual exact ray tracing analysis. Preoperative and postoperative data were analyzed using the Student's t-test and the Pearson coefficient.


124 patients were analyzed. 48 with 5 mm segments: 24 with 1X210º, 12 with 1 X 160º, 12 with 2X160º). 76 with 6 mm ICRS: 14 with 1X 210º, 26 with 1X150º, 12 with 1X150º + 1X90º and 24 with 2X120º. Globally Kmax, asphericity, high order aberrations, coma, astigmatism, BCVA, spherical equivalent showed a very significant change (p< 0,001). The results with each combination were studied. For example Kmax changed -1.25 ± 3.291 diopters in 6 mm 210º segments and -3.92 ± 3.269 diopters in 210º 5 mm segments (p=0.021). VSR correlated poorly with BCVA with BCVA (Coefficient 0.2, p=0,035).


This study shows that the strategy of customizing arc, width and optical zone of the segments according to the tomography of the patient is highly effective. Corneal changes with different segments should be analyzed in a separate way in order to find the most accurate clinical algorithm. VSR improves after ICRS implantation and new algorithms targeting the best VSR may be useful. The predictability of ICRS surgery is limited by the variability in topography and biomechanics in keratoconus patients. Bigger studies using this methodology can give us a better understanding of this technique.

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