If the K Measurements Differ Between Different Methods, Which One Should I Use?

Accurate corneal astigmatism measurements must be obtained to make sure you achieve success with toric intraocular lenses (IOLs). Many different devices are currently available to measure keratometry (K) values and corresponding meridians. Our preferred method to measure K-values is with the IOLMaster (Carl Zeiss Meditec). In our experience, the automated keratometry feature of the IOLMaster minimizes problems related to human errors. Furthermore, it is a reliable tool in spherical power calculations. In addition, because the IOLMaster always performs 3 repeated keratometry measurements, you can be sure that reliable and repeatable K-value measurements are taken. To measure astigmatism meridians, we compare measurements obtained with the IOLMaster, a corneal topographer, and a manual keratometer. In most patients, the values between the IOLMaster and corneal topographer are consistent with each other within 5 degrees. In these patients, we use the measurements obtained with the IOLMaster. If the discrepancy is more than 5 degrees, you have to be careful. First, you should confirm that measurements obtained with both devices are of good quality, reliable, and that no irregular corneal astigmatism (eg, due to keratoconus) exists. In our clinic, all patients who choose to have a toric IOL undergo manual keratometry using the Javal-Schiøtz keratometer (Rodenstock), which we still regard as the gold standard for meridian determination. In patients with a 5-degree difference between the astigmatism meridians obtained with the IOLMaster and corneal topographer, we usually use the meridians measured with the Javal-Schiøtz keratometer.