Purpose: To develop and evaluate an algorithm for corneal power estimation in intraocular lens (IOL) power calculation after laser refractive surgery for Asian Chinese patients.
Methods: Corneal parameters of Asian Chinese and European Caucasian were investigated by rotating Scheimpflug camera (Pentacam), and compared by statistical analysis Corneal power was simplified as a corrective algorithm: K_corrective=1.114×measured K +K₂ (K₂=K_posterior-K_anterior×K_posterior×corneal thickness/1.376, K_anterior =anterior corneal power; K_posterior=posterior corneal power), known as Maloney method. The variation and the change ofK₂induced by refractive surgery were analyzed. The corrective algorithm for Asian after refractive surgery was identified to be K_corrective=1.114×measured K-6.2, which was different with that of Caucasian. The algorithm was evaluated by 42 post-refractive cataract cases.
Results: No difference in anterior corneal radius (Ra) was found between the two samples. Posterior corneal radius (Rp), corneal thickness(CT), Ra/Rp ratio, keratometric index andK2were different between the two populations. MeanK₂was -6.22±0.24 D for Asian and -6.10±0.23 D for Caucasian, respectively (P<0.01). Mean change of K₂ induced by refractive surgery was -0.04±0.10D D. Low variations of K₂ were observed: 95% confident intervals ofK₂were -6.55 to -5.65 D (normal cornea), -6.48- to -5.70 D (pre-refractive), and -6.49 to -5.83 D (post-refractive). The algorithm provided the lowest prediction error (0.61±0.47 D) and tended to avoid underestimation of IOL power in post-refractive cataract cases for Asian patients.
Conclusions: The modified algorithm is a relatively reliable method in IOL power calculation after myopic laser refractive surgery for Asian Chinese patients.