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# 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).

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:

Credit : Zeiss IOL Master 700 Barret Suite

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