Ferrara ring’s effects on corneal asphericity in keratoconus treatment

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In keratoconus treatment, Ferrera® rings nomogram integrates the Q factor defining corneal asphericity. Our study deals with the effect of the implantation of Ferrerra rings on the Q factor


This retrospective and monocentric study involves forty eyes of thirty-one patients suffering from keratoconus implanted with Ferrara® rings, with an uncorrected visual activity (UCVA), a best spectacle-corrected visual acuity (BSCVA) and a videokerato-topography, before and six months after surgery. The items followed are the UCVA, the BSCA, the average (Kmean) and maximum keratometry (Kmax) and the Q factor in the central 20° (Q20) and 40° (Q40). The analyse of the visual acuity (more or less than a line) enables to differentiate two groups of “good” and “bad” responders. The statistical tests are a Wilcoxon signed rank for pre and post operative comparisons, a Wilcoxon-Mann Whithey for group comparisons, and a Spearsman for correlations.


The average age of patients is 32,8 years with 83,1% of male gender. Twelve eyes were implanted with two rings and twenty-eight with one. We find an average gain of 3.6 lines for UCVA, 1.1 lines for BSCVA and a decrease in Kmean of 1,4 dioptry. Q20 and Q40 are meaningly improved after surgery, but there is no significant difference between the studied groups. Lastly, before surgery, BSCVA is correlated to Q20, and Kmax to Q40. After surgery, UCVA is correlated to Q20 and Kmax to Q20. But the Kmax variation and the UCVA or BSCVA gains are not correlated.


Including the Q factor in the nomogram establishing ring’s choice improves the keratometric field but not the visual outcome.

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