IOL Adjustment & Residual Astigmatism with Incision Axis

For a non-toric IOL, sets the sphere to 0.00 and estimates the expected residual astigmatism — vectorially from corneal K values, axis, incision axis and surgeon factor (SIA).

Dr. Harald C. Gäckle · Refractive Planning Suite · Dr. med. Harald C. Gäckle · eagleyedrgaeckle@icloud.com

1 · IOL & target sphere

Proposed standard IOL (D)

Expected postop spherical equivalent (SE per biometer, without correction, D)

The SE the IOLMaster shows for the proposed IOL. In cylinder notation there is then usually a small plus sphere up front.

Conversion factor IOL → spectacle plane

1.0 D IOL ≈ 0.7 D refraction. Typically 0.65–0.80.

IOL step size

2 · Corneal astigmatism & incision

K2 is the steep meridian (higher power). Astigmatism = K2 − K1.

K1 – flat (D)

K2 – steep (D)

Axis of steep meridian (K2) 90°

Location of the steep corneal meridian (K2).

Incision axis (cut location) 180°

Where the surgeon cuts. The cornea flattens in this meridian.

Surgeon factor / SIA −0.25 D

Flattening in the incision meridian. Clear cornea approx. −0.25 D. Negative = flattening.