Biometry is a measurement of the length of the eye (front to back). It is an essential measurement prior to cataract surgery, as it influences the power of artificial lens implant that will be placed into your eye (to replace your natural lens that is being taken out). When the correct power of artificial lens is used, images are focused on the retina (back of the eye) and you can see clearly. If too much or too little power is used, images will be focused in front of or behind the retina, and you will see blurry.
To measure the length of your eye, sound waves (ultrasound A-scan) or light waves (optical biometry) are reflected off the back of your eye to assess distance. These sound and light waves are not harmful to your eye.
Ultrasound/A-scan: A numbing drop will be applied to your eye which takes effect immediately and lasts for about 20 minutes. Your vision will not be affected. A cup will be placed onto the eye, and filled with a water solution. The ultrasound probe will be gently placed into this solution so it can take the measurements. You will not feel the probe. Each eye only takes a few minutes. Contact lenses should not be worn for 2 weeks prior to testing.
Optical Biometry: You will be seated in front of a machine and asked to look at a light. It is important to be as still as possible. This test should not be painful, and will only take a few minutes.