The test is usually done in the ophthalmologist's office or the ophthalmology department of a hospital or clinic.
Your eye is numbed with medicine (anesthetic drops). The ultrasound wand (transducer) is placed against the front surface of the eye.
The ultrasound uses high-frequency sound waves that travel through the eye. Reflections (echoes) of the sound waves form a picture of the structure of the eye. The test takes about 15 minutes.
There are two types of scans -- A-scan and B-scan.
For the A-scan:
You will usually sit in a chair and place your chin on a chin rest. You will look straight ahead.
A small probe with some oil on it is placed against the front of your eye.
The test may also be done with you lying back. With this method, a fluid-filled cup is placed against your eye to do the test.
For the B-scan:
You will be seated and you may be asked to look in many directions. The test is usually done with your eyes closed.
A gel is placed on the skin of your eyelids. The B-scan probe is gently placed against your eyelids to do the test.
How to prepare for the test
No special preparation is needed for this test.
How the test will feel
Your eye is numbed, so you shouldn't have any discomfort. You may be asked to look in different directions to improve the ultrasound image or so it can view different areas of your eye.
A lubricant placed on the ultrasound wand may run on your cheek, but you won't feel any discomfort or pain.
Why the test is performed
Your doctor may order this test if you have cataracts or other eye problems.
An A-scan ultrasound measures the eye to determine the right power of a lens implant before cataract surgery.
A B-scan is done to look at the inside part of the eye or the space behind the eye that can't be seen directly. This may occur when you have cataracts or other conditions that make it hard for the doctor to see into the back of your eye. The test may help diagnose retinal detachment, tumors, or other disorders.
For an A-scan, measurements of the eye are in the normal range.
For a B-scan, the structures of the eye and orbit appear normal.
What abnormal results mean
A B-scan may show:
Bleeding into the clear gel (vitreous) that fills the back of the eye (vitreous hemorrhage)
To avoid scratching the cornea, do not rub the numbed eye until the anesthetic wears off (about 15 minutes). There are no other risks.
Fisher YL, Nogueira F, Salles D. Diagnostic ophthalmic ultrasonography. In: Tasman W, Jaeger EA, eds. Duane's Foundations of Clinical Ophthalmology. 15th ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2009:chap 108.
Coleman DJ, Silverman RH, Rondeau MJ, Daly SW, Lloyd HO. Evaluation of the posterior chamber, vitreous and retina with ultrasound. In: Tasman W, Jaeger EA, eds. Duane's al Ophthalmology. 15th ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2009:chap 3.
Massoud TF, Cross JJ. The orbit. In: Adam A, Dixon AK, Grainger RG, Allison DJ, eds. Grainger & Allison's Diagnostic Radiology. 5th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2008:chap 61.
Fisher YL, Klancnik Jr JM, Rodriguez-Coleman H, et al. Contact B-scan ultrasonography. In: Yanoff M, Duker JS, eds. Yanoff & Duker: Ophthalmology. 3rd ed. Philadelphia, Pa: Mosby Elsevier; 2008:chap 6.7.
Linda J. Vorvick, MD, Medical Director, MEDEX Northwest Division of Physician Assistant Studies, University of Washington School of Medicine; and Franklin W. Lusby, MD, Ophthalmologist, Lusby Vision Institute, La Jolla, California. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.