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Wavefront changes after implantation of a double arc intracorneal ring segment (ICRS) in keratoconic eyes

Poster Details

First Author: H.Melo BRAZIL

Co Author(s):    C. Oliveira   E. Nakano   P. Caddah   M. Machado   J. Filho        

Abstract Details


To verify wavefront and modulation transfer function (MTF) changes in a double arc ICRS implantation as a new concept for the treatment of keratoconus.


This multicenter, prospective, randomized study is being conducted at Federal University of São Paulo (UNIFESP) and at Hospital Oftalmológico de Brasília (HOB).


Forty eyes of selected patients were divided into group A (K max up to 60D) and B (K max from 61 to 75D). Eyes were also divided into two sub-groups according to the corneal astigmatism. Corneas with topographic astigmatism up to 5D received a 330 degrees segment; and those with higher amounts of astigmatism received two 160 degrees segments. Stromal tunnel was made with femtolaser at 75% depth of the thinnest point at 5mm central diameter zone. Aberrometry was measured with OPDScan III. MTF and Strehl Ratio values were derived from the OPD data.


Preoperaively, the correlation between high order aberrations root mean square ( HOA RMS) and coma was stronger (R2 = 0.5815), than between HOA RMS and spherical aberration (SA) (R2= 0.1581). HOA RMS varied from 1.806 to 1.698, 1.773 and 1.783, whereas Coma RMS varied from 1.113 to 1.414, 1.239 and 1.302 , meanwhile, SA RMS changed from 0.323 (C12= -0.288 micra) to 0.831 (C12=-0.733), 0.785 (C12= -0.705) and 0.802 (C12= -0.789), respectively in preop, 7 days, 30 days and 3 months after the surgery. Correlation between HOA RMS and coma RMS remained stronger throughout the postop period when compared to the correlation between HOA RMS and SA RMS.


The implant of a double arc ICRS led an increase of negative SA, denoting a centration of the prolapsed area of the cornea towards the vertex, also observed on topographic images. HOA RMS did not significantly change overtime and it was strongly related to coma. HOA MTF and Strehl Ratio did not suffer significant difference overtime.For future analysis, the use of a 35D curvature ICRS profile has been considered to better modulate negative SA induction, as well as to better flatten the corneal K max. Astigmatism has decreased significantly, still no change in coma was observed.

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