Table 1 Parameters of Alpins vector analysis method.

From: The correlation between ocular residual astigmatism and wavefront-guided FS-LASIK correction effects in myopic astigmatism patients

Parameters

Meaning

Target induced astigmatism vector (TIA)

TIA is the astigmatism vector that needs to be corrected to achieve the desired refractive state. If the target refractive power is 0, TIA is equivalent to the preoperative astigmatism

Surgically induced astigmatism vector (SIA)

SIA is the actual astigmatism vector corrected by the surgery, which equals to the vector difference between the preoperative and postoperative astigmatism

Difference vector (DV)

DV is the vector difference between TIA and SIA, representing the astigmatism that was not corrected by the surgery. The ideal value is 0

Angle of error (AE)

AE is the axial deviation between the SIA and the TIA. The ideal value is 0. A negative AE indicates a clockwise deviation, while a positive AE indicates a counterclockwise deviation

Correction index (CI)

The value is equal to |SIA| / |TIA|, which can be used to adjust the amount of astigmatism correction to achieve full correction. A value greater than 1 indicates overcorrection

  1. TIA target induced astigmatism vector, SIA surgically induced astigmatism vector, DV difference vector, AE angle of error, CI correction index.
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