Eye clinic / patient information
Ocular biometry
Ultrasound biometry measures the axial, front-to-back length of the eye using ultrasound waves. A one-dimensional A-scan is used for this measurement.
- Method
- One-dimensional A-scan measurement using ultrasound waves
- Measurement
- Axial length and other values used in intraocular lens calculation
- Purpose
- Planning the intraocular lens for cataract surgery
How ultrasound biometry works
There are two methods. With immersion biometry, the ultrasound probe is placed in a fluid-filled shell positioned over the cornea. With contact biometry, the probe is placed against the surface of the cornea. The probe is directed towards the back of the eye, in the direction of the macula.
The ultrasound wave travels through the eye until it reaches a boundary between structures. Part of the ultrasound energy is reflected back to the probe and recorded as an echo. When the speed of ultrasound through each medium is known, the instrument can calculate the distance between the recorded echoes and therefore the axial length of the eye.
When axial length is combined with corneal curvature measurements and the selected calculation formula, the instrument helps determine the power of the intraocular lens to be implanted during cataract surgery. The final lens plan is made by the ophthalmologist in the context of the complete examination and the patient's visual requirements.
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