Corneal astigmatism commonly overestimated, underestimated
Four diagnostic devices overestimated with-the-rule astigmatism and underestimated against-the-rule astigmatism in cataract surgery, according to a study.
The prospective study included 41 eyes of 41 patients. Preoperatively, 17 patients had with-the-rule astigmatism with a corneal steep meridian at 60° to 120°, and 24 patients had against-the-rule astigmatism with a corneal steep meridian at 0° to 30° or 150° to 180°.
Investigators used five devices to measure corneal astigmatism before cataract surgery and 3 weeks postoperatively. Toric IOL alignment was recorded at the slit lamp during surgery and 3 weeks after surgery.
The devices used were the IOLMaster (Carl Zeiss Meditec), the Lenstar (Haag-Streit), the Atlas corneal topographer (Carl Zeiss Meditec), a manual keratometer and the Galilei combined Placido-dual Scheimpflug analyzer (Ziemer).
Actual corneal astigmatism was based on refractive astigmatism 3 weeks after surgery. The 2 formula was used to calculate effective toric power. Prediction error was the difference between astigmatism measured with each device and actual corneal astigmatism.
Mean prediction errors for with-the-rule astigmatism were 0.59 D at 89.7 with the IOLMaster, 0.48 D at 91.2 with the Lenstar, 0.51 D at 78.7 with the Atlas, 0.62 D at 97.2 with the manual keratometer and 0.57 D at 93.9 with the Galilei.
Mean prediction errors for against-the rule astigmatism were 0.17 D at 86.2 with the IOLMaster, 0.23 D at 77.7 with the Lenstar, 0.23 D at 91.4 with the Atlas, 0.41 D at 58.4 with the manual keratometer and 0.12 D at 7.3 with the Galilei.
In against-the-rule eyes, with-the-rule prediction errors were 0.2 D to 0.3 D with all devices except the Galilei. The errors were statistically significant (P < .05).
Disclosure: See the full study for a complete list of all authors’ relevant financial disclosures.