IOL Power Calculator

Calculate intraocular lens (IOL) power for cataract surgery using the simplified SRK/T formula based on axial length and keratometry.

Axial Length

Average Keratometry (K)

Target Refraction

A-Constant

Tab to move between fields

Recommended IOL Power

20.5 D

Expected Refraction

0 D

Calculated IOL (unrounded)20.5 D

How to Use This Calculator

Enter the Axial Length in mm as measured by A-scan biometry or IOLMaster (normal range 22–25 mm).
Enter the Average Keratometry (K) in diopters — use the average of K1 and K2 corneal curvature readings.
Set your Target Refraction in diopters (0 = emmetropia; negative values for slight myopia post-op).
Enter the A-Constant for your specific IOL model (provided by the manufacturer, typically 118–119).
Review the Recommended IOL Power (rounded to nearest 0.5 D) and Expected Refraction with that implant.

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Formula

IOL = A - 2.5 × AL - 0.9 × K

Convert between Snellen fraction, LogMAR, decimal acuity, and MAR notation for visual acuity measurements.

Convert your glasses prescription to contact lens prescription using vertex distance adjustment for powers above ±4D.

Adjust lens power when changing the vertex distance (e.g., from glasses to contacts or between different frame positions).

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