The Emmetropia Verifying Optical (EVO) Formula is an advanced intraocular lens (IOL) formula for cataract surgery. It is based on the theory of emmetropization and generates an 'emmetropia factor' for each eye. As a thick lens formula, it takes into account of the optical dimensions of the eye, and can handle different IOL geometry and powers.


- Use ULIB or IOLCon SRK/T A constant for optical biometry and manufacturer's A constant for ultrasound biometry
- Select 'AR40e/E/M' for J&J Vision AR40e, AR40E, AR40M IOLs
- Select 'MA60MA' for Alcon MA60MA, MA60AC, MN60AC IOLs
- Select 'Standard' for other IOLs (eg. SN60WF, ZCB00, Bausch & Lomb, Hoya, Nidek, Zeiss)

The EVO Toric Formula is a toric IOL formula based on the EVO Formula. It combines theoretical posterior cornea astigmatism prediction, thick lens modelling for different types of toric IOLs, and a dynamically interconnected prediction of IOL power and toricity.


- Select the appropriate model depending on the location of the IOL toric surface / IOL type
- Anterior (eg. Tecnis, RayOne Toric, RayOne EMV Toric)
- Bitoric (eg. Zeiss)
- Posterior (eg. Alcon, Hoya, Physiol, RayOne Trifocal Toric)

Note: The EVO IOL calculator is solely intended for use with a pseudophakic IOL during cataract surgery and not for use with a refractive phakic IOL such as Staar Surgical's EVO Visian ICL