4.3.- Case 2. Corneal astigmatism magnitude 0.9D and ATR

Here we have the second example for the interpretation of the plot. The analysis corresponds to Right eyes with corneal incisions of 2.5 mm at temporal location. We filtered for corneal astigmatism <0.9 D and preoperative against-the-rule.

The questions to solve are:

  • What type of astigmatism do we have induced? With-the-rule because the square point is at the left side of the plot.
  • Is the SIA significant? Yes, because red ellipse is not cutting the center of coordinates.
  • What is the mean SIA magnitude and orientation? 0.37@88º
  • Do we have to consider SIA in future calculations of the IOL? We can do it. Although in the analysis of individual cases the results might be not improved because the center of the plot is inside of the blue ellipse, if we consider a sample of several cases the results might be improved
SIA calculator


The incision that is required for IOL implantation during cataract surgery induces astigmatism —this is referred to as surgically induced astigmatism (SIA)— so the total amount of astigmatism to be corrected with the toric IOL must consider the flattening (FE) or steepening (SE) effect on the meridian of the preoperative corneal astigmatism on which the IOL is going to be aligned. The SIA will depend on several factors, including incision type, location and size, and its design or architecture. 

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