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    Axial Eye Length Biometry

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    What is an Axial Eye Length Biometry?

    Axial Eye Length Biometry ("A-Scan" or "Biometry"), uses sound waves to measure the length of the eye and the thickness of structures inside the eye. A medical eye doctor (Ophthalmologist) uses these measurements to evaluate your eyes prior to cataract surgery. Also, the doctor uses these measurements to choose a new lens for you. This lens will be placed inside the eye once the cataract is removed. A specially trained technician (also referred to as a Registered Ophthalmic Ultrasound Biometrist – ROUB) performs this test.

    Note: This test uses low frequency ultrasound. To date, there are no confirmed adverse effects in humans caused by exposure to diagnostic levels of ultrasound.

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    What Can I Expect While at California Pacific Medical Center?

    Before the Test

    • Call (415) 600-3937 to schedule an appointment.


    • Go to the Ophthalmic Diagnostic Center at 2100 Webster Street, Suite 219.


    • Bring your insurance information with you to the appointment.
    During the Procedure, Your Technician
    • Places drops in your eyes to numb them for about 15 minutes. Your eyes will not be dilated. You will not feel any discomfort during this test.


    • Takes you into the Ultrasound suite and positions you comfortably in a slightly reclined position.


    • Places a small device on the eye to hold the lids open.


    • Uses a small probe to direct sound waves into the eye for the measurements. You will not be aware of this process. Measurement of each eye takes approximately 5 minutes. Generally speaking, both eyes are measured at the same time.


    • Lastly, after the measurements are completed, the technician removes the device and rinses the eye with a sterile saline solution. You should NOT rub your eyes with any tissue for 30 minutes.


    • Your eye measurements are given to your medical eye doctor prior to your surgery.
    After the Test
    • You may drive after this test, but plan for a 20-minute break after the test prior to driving. Check with the staff before you leave to ensure you are safe to drive.


    • You may resume your normal activities 20 minutes after the procedure when your eyes return to your normal vision.


    Frequently Asked Questions

    Question: During this test, a specially trained technician uses ultrasound to measure structures within the eye. True or False?
    Answer: True. Axial Eye Length Biometry is the measurement, using ultrasound, of structures within the eye.

    Question: Is this test painful?
    Answer: Axial Eye Length Biometry is a completely painless test.

    Question: Can I drive home after Axial Eye Length Biometry?
    Answer: You should not drive home immediately after this test. You should plan for a 20-minute break after the test prior to driving. Check with the staff before you leave to ensure you are safe to drive.


    Produced by the Center for Patient and Community Education in association with the staff and physicians at California Pacific Medical Center. Last updated: 1/05

    Photo by: Denice Barsness, CRA, COMT, ROUB, FOPS


    Funded by: A generous donation from the Mr. and Mrs. Arthur A. Ciocca Foundation.

    Note: This information is not meant to replace any information or personal medical advice which you get directly from your doctor(s). If you have any questions about this information, such as the risks or benefits of the treatment listed, please ask your doctor(s).

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