A-scan
This is a type of ultrasound used on the eye and is primarily used to measure the length of the eyeball. This measurement is needed prior to cataract surgery so that we can calculate the correct implant power for the replacement lens. A-scan ultrasound can be very precise but only focuses on one parameter – the length of the eye. This is in contrast to B-scan ultrasound, which actually produces an image of the interior structures of the eye (and is more akin to the fetal ultrasound used in pregnancy).
I use A-scan mainly to measure the length of the eye prior to cataract surgery. With cataract surgery, we remove the cloudy lens and place a new plastic “implant” lens inside the eye. These implants come in different prescriptions (like contacts). The a-scan helps us calculate the proper prescription to use.