What is an A-scan?
A-scan biometry uses sound waves to measure the axial length of the eye. Combined with corneal measurements, it allows your surgeon to calculate exactly which intraocular lens (IOL) power will give you the best possible vision after cataract surgery.
Why accuracy matters
The right IOL power is essential for a sharp result and reduced dependence on glasses. A-scan biometry is a quick, painless and important step in planning your cataract surgery.
What is the full form of A-scan?
A-scan stands for Amplitude scan, also called A-mode scan. It is a form of amplitude-mode ophthalmic ultrasound, which means it uses sound waves and displays the returning echoes as peaks of amplitude on a line. This information is used to measure the axial length of the eye, the front-to-back distance from the cornea to the retina. That length is a key value in planning cataract surgery.
How A-scan biometry works
A small ultrasound probe sends pulses of sound into the eye. As these pulses meet the different structures of the eye, they bounce back as echoes, and the time taken for each echo is used to measure the axial length. This length, together with corneal (keratometry) readings, is entered into a formula to calculate the intraocular lens (IOL) power needed before cataract surgery. The aim is to choose a lens that gives you the clearest possible vision afterwards.
A-scan vs B-scan
An A-scan and a B-scan both use ultrasound, but they do different jobs. The A-scan measures distances, chiefly the axial length, and is used for lens power calculation. The B-scan produces a two-dimensional picture of the structures inside and at the back of the eye, which helps assess the retina and vitreous when the doctor's direct view is blocked. Your doctor decides which scan, or both, is needed in your case.