Refractive & IOL

Astigmatism Vector Analysis — Alpins Vector Method Clinical Guide

📅 2026-05-26⏱️ 约6分钟

Alpins polar vector method for astigmatism analysis, calculating SIA/TIA/CR, quantifying corneal astigmatism correction effectiveness.

astigmatism vectorAlpins vectorSIATIADRCAcorrection index

Why Vector Analysis is Needed

Conventional arithmetic subtraction (postoperative - preoperative) ignores the axis characteristics of astigmatism and cannot accurately reflect the true surgical effect. Vector analysis considers both the magnitude and axis of astigmatism.

Core Concepts

TIA (Target Induced Astigmatism)

The amount of astigmatism planned to be corrected in surgery.

SIA (Surgically Induced Astigmatism)

Astigmatism change caused by surgical incision itself, typically 0.25-0.75D.

DRCA (Difference Between Reached and Calculated Astigmatism)

Actual residual astigmatism after surgery; ideally <0.5D.

CR (Correction Index)

CR = SIA / TIA:

  • CR = 1.0: Perfect correction
  • CR < 1.0: Undercorrection
  • CR > 1.0: Overcorrection

How to Use

  1. Enter preoperative corneal astigmatism (magnitude and axis)
  2. Enter surgical incision parameters
  3. Tool calculates SIA estimated value
  4. Output: Expected residual astigmatism, correction index

References

  • Alpins NA. A new method of analyzing vectors. J Cataract Refract Surg. 1993.
  • Alpins NA. Vector analysis of astigmatism. J Cataract Refract Surg. 1997.