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Intrastromal corneal ring segments in the refractive and therapeutic correction of paracentral keratoconus with perpendicular topographic and coma axes

Poster Details

First Author: L.Fernández-Vega Cueto SPAIN

Co Author(s):    C. Lisa   J. Merayo   J. Alfonso              

Abstract Details


To assess the visual results of the implant of Ferrara-type intrastromal ring segments (ICRS) for the therapeutic and refractive correction of keratoconus with perpendicular topographic and coma axes and coincident coma and refractive axes.


Instituto Oftalmológico Fernández-Vega,Oviedo,Spain


Retrospective study including 20 eyes from 20 patients, with mean age of 28 years. All eyes were diagnosed of paracentral keratoconus, with perpendicular topographic and coma axes and coincident refractive and coma axes (defined by us, by its characteristic topographical shape, as “Snowman” type 2 phenotype). All eyes were implanted with an inferior ICRS, whose axis coincided with the coma-refractive axis, through a Femtolaser-performed tunnel at 70% of corneal depth. Before surgery and three months after visual acuity, refraction, keratometry coma aberration and asphericity were recorded and evaluated.


At three months manifest sphere had reduced from -1.60±3.86 to -1.31±3.67 diopters (D), manifest cylinder had reduced from from -2.43±1.18 to -1.22±0.91 D and uncorrected distance visual acuity (UDVA) had improved from 0.34±0.21 to 0.50±0.34 and, for distance corrected visual acuity (DCVA) from 0.75±0.24 to 0.89±0.15. The flattest K had reduced from 46.63±4.15 to 45.00±4.44 D, and the steepest was approximately the same as before surgery. The keratometric cylinder increased from 2.23±1.13 to 3.97±0.81 D. Coma value had reduced from 2.61±1.34 to 1.66±1.48 microns, which reflects in the visual improvement achieved. Corneal asphericity changed from -0.85±1.27 to -1.70±1.99.


Paracentral keratoconus with perpendicular topographic and coma axes and coincident coma and refractive axes (Snowman type 2) benefit significantly from the implant of a Ferrara-type ICRS in the coma-refractive axis. With this surgical approach UDVA and DCVA, as well as manifest refraction improved despite of the worsening of the topographic cylinder.

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