Zeiss has launched the much-anticipated update to its IOLMaster 700 with swept-source biometry - total keratometry (TK) - described as a unique way to implement posterior corneal surface measurement into intraocular lens (IOL) power calculations.
This milestone builds on almost 20 years of experience in optical biometry and replaces assumptions with measurements, said Franziska Klatt, Zeiss ANZ’s surgical cataract product manager. “The current standard in IOL power calculation is based on a measurement of the anterior corneal surface and an estimate of the total corneal power by using eye model assumptions or nomograms. This does not address outliers in cases of unusual corneas, which could result in refractive surprises.”
The Zeiss IOLMaster 700 with TK differs from most established methods for total corneal power assessment because it considers corneal thickness and posterior corneal curvature in addition to the anterior corneal curvature measurements, said Klatt. This way, each eye’s posterior curvature is considered individually… (so) outliers in IOL calculation can be minimised.
Total keratometry has the potential to reduce refractive surprises to a minimum, said Professor Graham Barrett, who has developed two new Barrett formulas exclusively for TK: the Barrett TK Universal II and Barrett TK Toric. Initial clinical results indicate TK improves toric IOL power calculations (Fabian and Wehner, 2018) and can be directly incorporated in classic IOL power calculation formulas, while existing optimised IOL constants, such as ULIB constants, can still be used.
