Index of Refraction

When you open a new database for the first time the dialog box above pops up. In general, for almost everyone especially those in the US, you should just click OK. You can manually change it later on this screen

Here are some questions from customers and answers from Dr. Holladay regarding this.

We just updated our software and have a question regarding the Wang/Koch adjustment. It is stated under the help information in the Holladay IOL Consultant that ALL commercially available Optical Biometers use an average index of refraction (1.3574). My doctor had me contact Carl Zeiss Meditec to check that since we use the IOL Master, and their clinical application specialist is telling me that the IOL Master uses a refractive index of 1.3375. We are not really sure how to apply this Wang/Koch adjustment? Can you please provide more information?

Apples and Oranges ... the Regressions by Koch are for both the LenStar and IOL Master. The index of refraction of 1.3375 is used by both to convert from keratometric power to front radius of curvature. The average ocular index of refraction used to convert from number of interference patterns to axial length is at an engineering level which you have no access. Read the discussion in the Wang-Koch article. Any way, if you have the IOL Master it is appropriate to turn on the adjustment.

Recently the system has not allowed me to change the refractive index from 1.3375 to 1.3320. I do quite a few calculations for accounts in Germany which use this index. I am now having to convert the k reading manually and then enter it in order to calculate powers.

The INDEX of REFRACTION we are talking about in the PROGRAM is the one that converts the K-reading to a Radius of Curvature. If the KERATOMETER uses 332.0/R (e.g. if a K is 45 D and is a ROC of 7.378 mm), then you may change it on the SETUP SCREEN, but it is global and for everyone. If you have the ROC available you may enter that directly, and avoid any problems. The reason I ask is that the FORMULAS (H1, H2, SRK/T, Hoffer Q) convert the RADIUS to NET INDEX of REFRACTION (1.3320 to 1.3315 usually) after the Ks are converted. So the INDEX OF REFRACTION is specific to the KERATOMETER, not the INDEX used for the IOL Power Calculation.