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February 16, 2007
A New Formula for Cataract Success
Review of Ophthalmology Feb 2007
A surgeon from Moorfields Eye Hospital in London, however, says he has developed BESSt, a formula that can estimate a post-refractive patient’s corneal power accurately without any pre-refractive surgery corneal data. Here’s how the formula works.The surgeon who developed the formula, Edmondo Borasio, did so while working as a fellow with Moorfields’ Dr. Julian Stevens. Their names, along with Moorfields colleague Guy T. Smith, make up the BESSt acronym: Borasio Edmondo Smith and Stevens.The BESSt formula is a modified version of a Gaussian optics formula, and was developed after studying 150 refractive surgery eyes.
In order to perform corneal power calculations using the BESSt Power Calculator, the surgeon must know the cornea’s anterior and posterior radii of curvature, as well as the central thickness. Dr. Borasio takes these values from the Oculus Pentacam, but he says that, theoretically, they could be acquired with an Orbscan and an ultrasonic pachymeter, though the accuracy of the formula wasn’t tested with the Orbscan. For IOL power calculations, he recommends getting the axial length measurement with an IOL Master (Carl Zeiss Meditec), because he says A-Scan ultrasound is less accurate. The surgeon also must have the target postop refraction and the IOL’s A-Constant.The BESSt Corneal Power Calculator is available for free at besstformula.com. This version provides corneal power only. A full-featured version costs about 90 pounds
Posted by mehdi khanlari at February 16, 2007 08:20 AM