Refractive Surgery · Calculation Tool

Toric IOL – Axis Positioning

Vector-based calculation of total corneal astigmatism from anterior and posterior surface (Pentacam / Galilei), including surgically induced astigmatism. Output: implantation axis and cylinder suggestion.

1 Eye & Anterior Surface

Anterior surface SimK values. Axis K2 = steep meridian.

2 Corneal Posterior Surface

Measured posterior values (Pentacam / Galilei)
Posterior surface negative values. Steep meridian = higher absolute power (typically vertical).

3 SIA & Incision

Temporal clear-cornea incision OD ≈ 180°, OS ≈ 0°. The incision flattens its meridian.

4 IOL Parameters

Ratio ≈ 1.46 as approximation; for the final order always use the manufacturer calculator (ELP-dependent).

5 Import Pentacam / Galilei

Photograph printout or drag image here
OCR extracts K values automatically – please verify before applying.
Recommended implantation axis
–°
Align IOL axis markings to the steep meridian of target astigmatism
Steep anterior Steep posterior IOL axis (target) Incision

Vector Result

Anterior astigmatism
–
Posterior astigmatism
–
TCA (total corneal)
–
Target incl. SIA
–
IOL cylinder (suggested)
–
Expected residual (corneal)
–
Target astigmatism < 0.75 D – toric IOL indication borderline; consider aspheric monofocal IOL.

Rotational Tolerance

Residual cylinder from misalignment: –
Each degree of misalignment loses ~3.3% of cylinder effect; beyond ~30° no net correction remains.
Module 2 · Biometry

IOL Power – Haigis & Haigis-L

Calculation from axial length, anterior chamber depth and mean keratometry. Haigis-L for eyes after myopic laser surgery (LASIK/PRK).

Verify constants. The stored A-constants are nominal manufacturer values; a0 is derived from them (a1=0.40 / a2=0.10). Before clinical use, replace with IOLcon-optimized, personalized a0/a1/a2. Barrett Universal II and Kane are proprietary and are deliberately not reproduced here — they are linked as official calculators instead.

A Biometry

Take mean K automatically from Module 1 (K1/K2)

B Corneal History

Status post myopic LASIK/PRK → Haigis-L
Haigis-L corrects the measured corneal radius via the published regression (Haigis 2008). Validated only for prior myopic surgery; for prior hyperopic surgery or K < 35 D prefer other methods (ASCRS calculator).

C Lens Library

a0 updates automatically when the A-constant is changed. Override a1/a2 for personalized optimization. Reference: IOLcon.org (formerly ULIB).

D Import Biometry Printout

Photograph IOLMaster / Lenstar / Anterion
OCR extracts AL, ACD and K – please verify before applying.
IOL power for target refraction
–D
Haigis · exact computed value (intermediate)

Power Steps & Expected Refraction

IOL (D)Exp. SE (D)

Intermediate Values

ELP (d, Haigis)
–
Corneal radius r
–
Corneal power (n=1.3315)
–
r corrected (Haigis-L)
–

Proprietary Formulas

Barrett Universal II and Kane are not simulated. Cross-check values in the official calculator:

Barrett Universal II ↗ Kane Formula ↗ ASCRS Post-Refractive ↗ IOLcon Constants ↗

Module 1 (toric axis): simplified vector-based calculation (double-angle addition). Module 2 (power): Haigis vergence formula with ELP = a0 + a1·ACD + a2·AL; Haigis-L radius correction per Haigis 2008 (myopic laser surgery). Both modules support planning and replace neither the manufacturer-specific or device-integrated calculator nor clinical judgment. A-constants are nominal and must be personalized on IOLcon.org before use. Always verify OCR results manually. © Eye Laser Centre – internal use.