Objective: To compare the accuracy of corneal topography, keratometer and cycloplegic retinoscopy in measuring astigmatism for refractive surgery.
Methods: Three hundred and sixty eyes with ametropia were randomly selected. The results of corneal topography, that of keratometer and cycloplegic retinoscopy in measuring astigmatism before refractive surgery were compared, and the measuring results of corneal topography and that of keratometer for 72 eyes after photorefractive keratectomy (PRK) and 95 eyes after laser in situ keratomileusis (LASIK) were also compared.
Results: No significant difference was found in axes of astigmatism among the three groups. As for diopters of astigmatism, there was no significant difference between the group of corneal topography (DeltaSim K) and the group of keratometer (DeltaK), but we found significant difference between the group of cycloplegic retinoscopy and the other two groups before and after refractive surgery. Significant difference was also found between DeltaSimK and DeltaK after PRK and LASIK.
Conclusions: Our investigation demonstrates that before refractive surgery the keratometer has a similar clinical value as that of corneal topography, and the DeltaSim K value is related to the graphic pattern of corneal topography. However, keratometer is limited in measuring mild changes in corneal curvature after refractive surgery, while the astigmatism expressed by DeltaSim K in corneal topography is more accurate.