EyeToolkit is a free online clinical toolkit for ophthalmologists and optometrists worldwide, offering clinically validated calculators — IOL power calculation, vision conversion, astigmatism analysis, IOP correction, myopia control, and more. All tools are free and require no registration.

Who are these ophthalmic tools for?

Primarily for ophthalmologists, optometrists, medical students, and other healthcare professionals. The tools are based on standard clinical formulas and support clinical decision-making, but do not replace a physician’s professional judgment.

Which formulas does the IOL calculator support?

It supports three internationally recognized IOL power calculation formulas — SRK-T, Hoffer Q, and Haigis — so you can choose the most appropriate formula for each patient.

Yes. All EyeToolkit tools are completely free and require no registration.

How can I contact EyeToolkit?

For feedback or collaboration, email eyetoolkit@foxmail.com.

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📚 User Guide

Formula Selection Guide

SRK/T — Normal to long axial length (AL ≥ 22mm), APACRS validated < 0.1D

Hoffer Q — Short axial length (AL < 22mm), tan angle fixed, difference < 1D

Haigis — Long axial length (AL > 26mm) / post-refractive surgery, constants need optimization

Input Parameters

• AL: Axial length (mm), measured by IOL Master

• K1/K2: Corneal power, flat/steep meridian (D)

• Target refraction: Expected postoperative refraction (emmetropia = 0.0)

• A-constant / pACD: Lens-specific parameters, refer to manufacturer specs

IOL Selection Reference

• High hyperopia / short AL: prefer high Abbe number lens, Hoffer Q

• Normal AL: SRK/T or Haigis, pick median when difference < 0.5D

• High myopia / long AL: SRK/T + Wang-Koch adjustment, or Haigis

Related Guides

IOL Formula Selector: Which IOL Power Formula Should I Use? decision tree by axial length, special populations, 5-step workflow.
IOL Power Calculation: The Complete Surgeon Guide formula comparison, constants, Wang-Koch adjustment.

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IOL Power Calculator

SRK/T · Retzlaff 1990 · Target -0.5D

⚠️ Clinical Disclaimer

① This tool is a surgical planning reference and does not replace IOL Master or other NMPA-certified medical device software.
② For use by licensed ophthalmologists only, after comprehensive patient assessment.
③ This tool is independently developed with no affiliation to any medical device manufacturer.
④ Results are for reference only. Final IOL power must be determined by the operating surgeon.
⑤ For complex cases (post-refractive surgery, extreme AL), cross-validate with Barrett official calculator (APACRS) or IOLMaster.

Ocular Biometrics

Axial Length AL (mm)

Corneal Power K1 (D)

Corneal Power K2 (D)

Target Refraction tgt (D)

Formula

IOL Selection

IOLAlcon SN60WF

SRK-T A118.7

Hoffer-Q pACD5.82 mm

TypeMonofocal

A-Constant Override

SRK-T A constant

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Enter parameters and click Calculate

📚 Clinical Sources

All calculations follow peer-reviewed, published formulas. The list below cites the primary literature for each model.

Retzlaff J, Sanders DR, Kraff MC. Development of the SRK/T intraocular lens implant power calculation formula. Journal of Cataract & Refractive Surgery, 1990;16(3):333-340.
Hoffer KJ. The Hoffer Q formula: a comparison of theoretic and regression formulas. Journal of Cataract & Refractive Surgery, 1993;19(6):700-712.
Haigis W, Lege B, Miller N, Zimmermann M. Comparison of immersion ultrasound biometry and partial coherence interferometry for intraocular lens calculation according to Haigis. Graefe's Archive for Clinical and Experimental Ophthalmology, 2005;243(8):780-787.
Wang L, Koch DD. An improved prediction of residual astigmatism in cataract surgery. Journal of Cataract & Refractive Surgery, 1999;25(3):407-411. — Wang-Koch adjustment for long / short AL.

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⚠️ Medical Disclaimer

This tool is for educational and clinical reference only, and does NOT constitute medical advice, diagnosis, or treatment. No doctor–patient relationship is created by using this tool. Always consult a licensed ophthalmologist for clinical decisions.

Questions or corrections? Email eyetoolkit@foxmail.com