Comparison of corneal thickness and biomechanical properties between North African and French patients.

Purpose: To determine whether corneal thickness and rigidity vary between French and North African refractive surgery candidates.

Setting: Three clinics in North Africa and 1 hospital in France.

Design: Cross-sectional study.

Methods: In part 1, the central corneal thickness (CCT) in North African patients and French patients having preoperative examinations was retrospectively compared. In part 2, the biomechanical properties of the corneas in the 2 groups were prospectively compared. Comparisons were performed using the Student t and chi-square tests and multivariate linear and logistic regression.

Results: The retrospective study comprised 1662 patients from North Africa and 221 patients from France and the prospective study, 249 and 110, respectively. After adjustment for sex, age, and steepest keratometry, the mean CCT was statistically significantly thinner in North African patients (P<.0001). More than one fourth of North African patients had corneas thinner than 500 μm (28.9% versus 7.7% of French patients). Of patients with thin corneas, the mean corneal resistance factor (CRF) was statistically significantly lower in North African patients (P<.0001); there was no significant difference in corneal hysteresis. This remained true after adjustment for CCT (CCT-adjusted difference in CRF between groups: -0.78; range -1.27 to -0.28; P=.002).

Conclusion: Corneas were thinner in North African patients than in French patients, and the CRF was different even when CCT was taken into accounted. More research is needed to determine whether these differences are associated with an additional risk for ectasia after laser in situ keratomileusis.