# Barrett A Constant to Lens Factor conversion and Design Factor

**For specific A constant to Lens Factor conversion table please click on the below link** : __https://www.quickguide.org/post/new-a-constant-to-lens-factor-lf-conversion-for-barrett__

or visit ' __New ! A constant to Lens Factor (LF) conversion for Barrett'__ in the Biometry section

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Friends, in the above video presentation I have in detail explained about the concept of ** Lens Factor (LF)**. In that post I had explained that the Lens Factor, is the distance from the Iris plane to the second principal plane of the IOL. To understand more about what is second principal plane, a term derived from Gaussian Optics, please follow

__(https://www.quickguide.org/post/all-about-gaussian-optics-gullstrand-eye-theoretical-and-ray-tracing-formula)__

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In the below table, you get the** Lens Factor (LF) and Design Factor (DF)** of some IOLs. An important concept is the **Design Factor (DF)** of the lens in the Barrett Universal formula. The design factor or DF of the Barrett Universal formula indicates when the IOL optic transforms from a biconvex design to a meniscus shape in case of low power IOLs. For example, in case of Alcon AcrySof lens, the IOL powers of 6 to 34 diopters are biconvex in design. All lens power below 6 diopter are available in meniscus design on the Acrysof platform (MA60MA). **Therefore the DF or design factor of Alcon AcrySof lenses are 5. That is from this all lenses above this model are biconvex in design**.

Similarly, the Design Factor of Tecnis ZCB00 is 4. That is, all lens power over this 4.0 diopter are biconvex in design. The Tecnes ZCB00 is available in +5.0 to +34.0 diopters all in biconvex shape. Therefore, the Design Factor (DF) of 4 indicates that all dioptric power from this company below 5.0 if available, are not biconvex in design.

Please remember all constants help you to fine tune the ELP/IOL Power in terms of where the IOL is sitting and how far it is sitting from the Cornea ( A constant in SRK T ), from the Iris Plane ( Surgeon Factor in Holladay I ), or the Iris Plane to second principal plane of IOL ( Lens Factor in Barrett Universal II ). **The Vivinex XY1/XY1A is not updated as on date. However the Barrett Universal Online Calculator displays a Lens Factor of 2.0 against the optical A constant of 119.23 as on June 2019** For a detailed list of Lens Factor against A Constant for those using the Barrett Formula, please visit:

__https://www.quickguide.org/post/new-a-constant-to-lens-factor-lf-conversion-for-barrett__

Credit : Zeiss IOL Master 700 Barret Suite

**To understand more about Lens Factor and Barrett Universal formula, please visit:**

__https://www.quickguide.org/post/the-science-behind-barrett-universal-ii-formula__