/ /

  • linkedin
  • Increase Font
  • Sharebar

    Why keratometry is important

    K readings provide a wealth of information

    Top 5 keratometry tipsKeratometry (K) is the measurement of the corneal curvature; corneal curvature determines the power of the cornea. Differences in power across the cornea (opposite meridians) results in astigmatism; therefore, keratometry measures astigmatism. It can be acquired with a variety of instruments either manually or via automated methods. Measurements can be very sophisticated, such as with topographers, that measure a cornea across a broad number of points, or it can be measured in a more finite area of the cornea, for example with a manual keratometer or with the IOL Master (Carl Zeiss Meditec). The IOL Master also measures the axial length and other ocular parameters (such as anterior chamber depth and white-to-white measurements) and includes K readings.

    Manual vs. automated

    Personally, I prefer manual keratometry because it provides a clear understanding of the integrity of the pre-corneal tear film, a dynamic view of the surface of the cornea. With manual keratometry, you have a direct visualization of the reflections generated by the tear film. You can recognize areas of corneal surface irregularity or compromise. If the tear film is oily or disrupted, or the cornea has subtle dystrophy or degeneration, it will be reflected in the quality of the measurements (akin to the changes of a pebble tossed into a placid lake). You have a much better understanding of the quality and accuracy of your measurements.  

    With automated measurements, acquisition is static. The measurements are acquired at a moment in time and computer generated. As the instrument operator, you have no appreciation of the accuracy of the “measured moment.”

    Keratometry is a critical measurement in cataract surgery because errors in measurements are matched 1:1 to refractive outcomes. If you’re 1.00 D off in your K readings, you will have a 1.00 D refractive surprise. If your K is inaccurate, you will have an unexpected refractive surprise post-operatively. In this generation of cataract surgery and premium intraocular lenses (IOLs), a refractive miss outcome is very disappointing to the doctor and the patient. Correcting residual ammetropia in cataract postoperative patients may require a second surgical procedure, be it IOL exchange, piggy-backing of an additional IOL, or a surface procedure.

    If there’s any doubt in your K readings, they should be redone on another day. We will repeat K readings if there is any indication of a problem or if the measurement is difficult to acquire. I typically measure the right eye, then the left eye, then repeat to verify.

    If I’m uncomfortable with any aspect of my measurement—if the patient has dry eye disease or comes in wearing contact lenses, for example—I will have the patient return after dry eye treatment and no contact lenses wear for 1 to 3 weeks, depending on the lens type. Your first K measurement may not be the one you use for surgery. If you’re taking measurements for cataract surgery, it’s the first thing you want to do before instilling drops, performing gonioscopy, or anything that may compromise the corneal surface.

    Although it’s not hard to learn, it takes a little practice to be sure you have accurate measurements in manual K. You need to be confident in your measurements before you put your findings down on a piece of paper. At Omni Eye Surgery, only doctors, including residents, will perform keratometry for patients planning cataract surgery.

    Some surgeons prefer the most updated automated K for their surgeries. It’s smart to compare manual with automated to get a better idea because each method measures different areas of the cornea; however, measurements should correlate. Also, you should expect correlation of the measured corneal cylinder with the patient’s spectacles.

    Next: The importance of an accurate reading

    Katherine M. Mastrota, MS, OD, FAAO, Dipl ABO
    Director of Optometry, New York Hotel Trades Council, Hotel Association of New York City, Health Center, Inc.


    You must be signed in to leave a comment. Registering is fast and free!

    All comments must follow the ModernMedicine Network community rules and terms of use, and will be moderated. ModernMedicine reserves the right to use the comments we receive, in whole or in part,in any medium. See also the Terms of Use, Privacy Policy and Community FAQ.

    • No comments available

    Optometry Times A/V