In the group of individuals with equal or greater than 0.75 D of astigmatism, when comparing the median axis of the astigmatism, setting the IOLMaster axis as the benchmark, 27 out of 57 (47%) of the eyes were within 0-4 degrees, 13 out of 57 (23%) were within 5-10 degrees, 12 out of 57 (21%) were within 11-20 degrees and 5 out of 57 (9%) were 21 degrees or more apart on the two instruments.

Disscussion of Keratometry Results:
Keratometry is the second most important factor in IOL calculation and sources of post-operative refractive error. It is impossible to tell which instrument truly measures the correct keratometry. Keratometry is location dependent and IOLMaster measures the K’s at 2.5 mm, yet the LENSTAR measures the K’s at 2.30 mm and 1.65 mm. Another factor is the axis of the keratometry.
Comparing the IOLMaster and the LENSTAR keratometry measurements revealed excellent correlation between the two instruments. The mean K as measured by each instruments showed 80% of the eyes were within 0.25 D. When only considering the amplitude of astigmatism (K1-K2), in the eyes with 0.75 D or more of astigmatism as measured by IOLMaster, 58% were within 0.25 D and 84% were within 0.5 D, with the caveat that LENSTAR typically measured smaller value. Additionally, 70% of eyes with 0.75 D or more of astigmatism had axis measurements within 10 degrees by both instruments.
As a clinician, I wonder, if there is any real clinical difference between the keratometry of the two instruments. Future projects should also consider how the inter-instrument correlation of similar make instruments would be. How would keratometric results of two IOLMasters, or two LENSTARs compare?
There is a tremendous amount of hype out there that one instrument is far superior in keratometry and calculations for TORIC IOLs. The current set of data clearly does not support such hype. Aside from "theoretical claims," I await to see real data and science behind the existing claims!
To continue with the study pages:
Keratometry (Current Page)