Biometry, also called as axial length measurement is a test that measures the axial length (distance between the front and back poles of your eye).
A. Ultrasound (called A Scan)
In the A Scan, your eyes are first numbed with anesthetic eye drops. A small device may be used to keep your eyes open. A probe is held perpendicularly touching the centre of your cornea (the front clear surface of your eye). This probe directs the sound waves into your eyes.
In Optical biometry, light is reflected rather than sound. There is no contact with your eye as a special camera does the work of the probe.
The results are entered into a computer which provides a measure of the distance between the various intra-ocular structures. This test takes about 10 to 15 minutes.
When cataract (clouding of the lens of your eye) occurs, your eyes lose the focusing power that the lens provides. In order to overcome this, your eyes are fitted with an artificial lens. However, so as to calculate the power of this artificial lens, your doctor needs to make a few measurements:
• the axial length of your eye
• the depth of the front chamber and thickness of the lens
Biometry is done in order to obtain these measurements before cataract surgery.