System combines Scheimpflug and Placido topographer

Ophthalmic surgeons have an array of methods available for calculating the power of an intraocular lens (IOL) to be implanted in cataract surgery, including Placido-disk corneal topography, automated keratometry, Scheimpflug camera imaging, and dual Scheimpflug camera imaging combined with Placido-disk corneal topography. Researchers now report comparative results obtained with a new system that combines a Scheimpflug camera with Placido-disk corneal topography, Sirius (Costruzione Strumenti Oftalmici). They compared the system in 38 eyes of 38 patients having phacoemulsification and in-the-bag IOL implantation. The calculated IOL power using the Hoffer Q, Holladay 1, and SRK/T formulas; the axial length, as measured by ultrasound immersion biometry; and three corneal power measurements: validated topographer simulated keratometry (K); combined Scheimpflug camera– topographer simulated K (derived from anterior corneal curvature only); combined Scheimpflug camera-topographer mean pupil power (derived from anterior and posterior corneal curvatures through ray tracing). When the corneal power measurements from the combined Scheimpflug camera-topographer were used, the mean absolute error (MAE) ranged between 0.23 D ± 0.24 (SD) (simulated K and Hoffer Q formula) and 0.33 ± 0.23 D (mean pupil power and SRK/T formula). There were no statistically significant differences between the MAE generated by the simulated Ks of the two devices with any of the three formulas.

 G Savini et al., JCRS, 'Accuracy of corneal power measurements by a new Scheimpflug camera combined with Placido-disk corneal topography for intraocular lens power calculation in unoperated eyes,' Vol 38, No. 5, 787-792.