A-SCAN ULTRASOUND
What is an A-scan?
An A-scan is an eye ultrasound that gives details about the length of the eye. Ultrasonic and light waves are used to measure dimensions of many parts of the eye. This includes the total length of the eye, the curvature of the cornea, the thickness of your natural lens. Why is it called an A-scan? A-scan is abbreviated for amplitude scan and it is a one-dimensional scan of the eye.
Why do I Need an A-Scan Before Cataract Surgery?
When cataract surgery is performed, the natural lens in the eye (the cataract) is removed and replaced with an artificial intraocular lens (IOL) implant. Every eye has a different size and shape. The power of the lens implant needed is different depending on the many measurements of the eye. Therefore, regardless of the type of IOL used, an A-scan ultrasound is necessary before surgery to provide precise measurements. The measurements allow the surgeon to select the lens implant power that is appropriate for your eye. This helps you achieve clear vision after your surgery.
How is an A-Scan Performed?
At City Eye Centre, we use the latest Zeiss IOL Master 700, a gold standard cataract biometer that provides precise measurements.
The IOLMaster device measures the length of the eye, in addition to the shape of the surface of the eye and the dimensions of other structures. At the same visit, we will perform a corneal scan to map the front surface of the eye. A macular scan will also be performed to look for abnormalities of the macular region.
What Happens If I Have Astigmatism?
If you have astigmatism, the A-Scan will provide us with precise information and when combined with special computerized calculations, allow accurate toric intraocular lens (IOL) selection. The toric IOL lenses will aim to correct your astigmatism and provide clear vision after surgery.
What Happens If I Normally Wear Contact Lenses?
If you normally wear contact lenses, it may take some time for the shape of the surface (the cornea) to “unmold” from the contact lens. This is because contact lenses change the corneal shape slightly. We advise that measurements are taken after the cornea is fully unmolded. Patients who wear soft contacts usually take about a week without contact lens use to unmold. Rigid gas permeable contact lens wearers take longer.
What are Other Uses of A-Scan Ultrasound?
In addition to its critical role in cataract surgery, an A-Scan ultrasound is important in tracking myopia progression. It is used to monitor for axial length changes when children or young adults are short-sighted. This ensures that myopia control, either with eye drops or contact lenses, is effective.
Do you have questions or concerns about your eye health or a specific eye condition? To discuss, please contact City Eye Centre for more information