IOL basics

This page explains the vocabulary used throughout the IOL Reference database — lens categories, materials, optic and haptic design, and the constants used in IOL power calculation.

Lens categories

Monofocal lenses provide a single focal point, usually set for distance. Toric lenses add cylinder power to correct corneal astigmatism and must be aligned on a specific axis. EDOF (extended depth of focus) lenses stretch a single elongated focus to add intermediate range. Multifocal and trifocal lenses split light between two or more distinct focal points.

Materials

Most modern IOLs are hydrophobic acrylic, hydrophilic acrylic, or silicone. Material affects refractive index, glistening behaviour, unfolding speed, and compatibility with silicone oil.

Design

1-piece lenses have haptics made of the same material as the optic and are designed for in-the-bag placement. 3-piece lenses have separate haptics and can be placed in the bag or the ciliary sulcus — see sulcus IOL placement.

A-constants

The A-constant characterises where a given lens sits in the eye for power calculation. Each lens page on this site lists both the optical A-constant and the US/SRK A-constant, because formulas and biometers differ in which they expect.

Browse the full database by manufacturer or look up a specific model number.