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PURPOSE:

We detected keratoconus cases with a significant potential for poor outcomes following intracorneal ring segment implantation (ICRS). We attempted to predict the potential of a case in terms of gain or loss of corrected distance visual acuity (CDVA).

METHODS:

In this retrospective and prospective, consecutive, nonrandomized, multicentric study, 58 keratoconic eyes (aged 1756) were implanted with the keraring using the femtosecond laser technology. The follow-up period was 6 months. keratometric, biomechanical, aberrometric, refractive, and visual variables were measured for two different groups: Group A included eyes that gained 0.2 or more in corrected distance visual acuity (CDVA, decimal scale) and group B included eyes that lost more than 0.15. Correlations between clinical parameters and changes in visual acuity were investigated. In addition, a linear regression model was developed using CDVA, apical keratometry (AK), and a new keratometric parameter defined and named by us as K-factor (K(F)).

RESULTS:

Significant differences between groups preoperatively were found for CDVA (P = 0.002), AK (P = 0.013), and K(F) (P = 0.025). The following predictive model was obtained using these variables: DeltaCDVA = -0.511 + 0.0007K(F)(p)-0.849CDVA(p)+0.008AK(p).$$ Predictability of the model was 0.797. Sensitivity was 88.1% and specificity 83.3%.

CONCLUSIONS:

The mathematical model predicts that this surgery is very effective in patients with preoperative CDVA (decimal scale) in the range of 0.01 to 0.3, predicting a gain of 3, 4, or even 5 lines. Gains are predicted and confirmed for CDVA between 0.3 and 0.5. For preoperative CDVA between 0.5 and 0.75 visual outcomes are doubtful. Higher values of CDVA often are related to a decrease in CDVA. This model may help surgeons to select the best cases for ICRS implantation and exclude the worst in terms of visual outcomes.