Prognostic factors of intracorneal rings segment to a successful treatment and probability of success calculation

PurposeTo identify prognostic factors for the success of intracorneal rings segment (ICRS) implantation in keratoconus, define a "good responder" patient, and estimate the probability of success of the intervention.MethodsIn this retrospective study, 130 eyes underwent ICRS implantation with Keraring and Intacs SK. Refractive, topographic, and aberrometric variables were measured before and after intervention, then patients were classified into "success" and "failure" groups based on postoperative refractive and aberrometric data. Univariate and multivariate analysis were performed to identify prognostic factors and develop a calculation formula for probability of success.ResultsSuccess was observed in 64.6% of patients while 35.4% experienced failure. In the success group, corrected distance visual acuity (CDVA) in logMAR was higher (0.38 ± 0.23 vs 0.28 ± 0.21, p = 0.03), corneal asphericity (Q-value) was less prolate (-0.92 ± 0.43 vs -1.10 ± 0.40; p = 0.009), and distance between Kmax and center of pupil (DKmax) was higher (1.65 ± 0.83 vs 1.35 ± 0.70; p = 0.045). Maximal keratometry (Kmax) was lower (58.38 ± 4.83 vs 59.86 ± 4.42; p = 0.068) and spherical equivalent (SE) was more negative (-3.77 ± 3.20 vs -3.05 ± 3.65; p = 0.09) but not statistically significant. With a logistic regression model, we created a calculation formula of the probability of success including keratoconus stage, CDVA, uncorrected distance visual acuity (UDVA), SE, Kmax, Q-Value and DKmax.ConclusionsICRS implantation has a higher chance of success in stage III keratoconus, eccentric, with myopic astigmatism, visual loss, Q-Value close to zero and low Kmax. The calculation of the probability of success helps to select patients for surgery.