Journal of Cataract & Refractive Surgery
Volume 29, Issue 5 , Pages 961-965, May 2003

Ultrasound axial length measurement in biphakic eyes

  • Kenneth J Hoffer, MD

      Affiliations

    • Jules Stein Eye Institute, University of California, Los Angeles, USA
    • St Mary’s Eye Center, Santa Monica, California, USA
    • Corresponding Author InformationReprint requests to Kenneth J. Hoffer, MD, St. Mary’s Eye Center, 1441 Broadway, Santa Monica, California 90404, USA.
    • The author has no financial or proprietary interest in any material or method mentioned.

Accepted 9 October 2002.

Abstract 

Purpose

To determine the calculations to correct the error in ultrasound measurement of a phakic eye with a phakic intraocular lens (IOL) (biphakic eye) to increase the accuracy of IOL power calculation should cataract surgery become necessary.

Methods

Mathematical derivations were performed to calculate the error caused by a phakic IOL while measuring an eye using an average sound velocity. A simple model was developed to allow correction of the axial length (AL).

Results

If the eye is measured at an average velocity of 1555 meters/second, the following calculation can be used depending on the material of the phakic IOL: ALcorrected = AL1555 + X × T, where T is the central thickness of the phakic IOL and X = +0.42 (0.41 – 0.42) for poly(methyl methacrylate), –0.59 (0.56 – 0.59) for silicone, +0.11 (0.10 – 0.12) for Collamer, and +0.23 (0.23 – 0.24) for acrylic.

Conclusion

By obtaining the dioptric power of the phakic IOL and central thickness from the manufacturer and knowing the material of the lens, a mathematical correction can be made to arrive at the true ultrasound AL in a biphakic eye.

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PII: S0886-3350(03)00293-1

doi:10.1016/S0886-3350(03)00293-1

Journal of Cataract & Refractive Surgery
Volume 29, Issue 5 , Pages 961-965, May 2003

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