- A-scan and B-scan are both types of ultrasound examinations performed for eye evaluation.
- A detailed eye examination tells not only about the structures of the eyes but also about any underlying health conditions such as high blood pressure and diabetes.
- Several techniques have evolved for the routine examination of the eyes or to plan eye surgeries (such as cataract surgeries). Ultrasonography techniques are important tools in evaluating eye diseases and performing eye surgery (ophthalmology).
- A-scan and B-scan are both eye ultrasonography scans. Although both the scans are based on the principle of ultrasonography, they differ in certain aspects.
A-scan
- A-scan is the short form for amplitude scan. This eye ultrasound gives details about the length of the eye.
- It is a one-dimensional scan of the eye.
- The measurement of the axial length of the eye through an A-scan is necessary for placing intraocular lens (IOL, artificial lens) during a cataract surgery.
- It may also be used to assess vision abnormalities of the eye and other diseases involving the eye such as tumors.
B-scan
- B-scan is considered the brightness scan. It is used for producing a two-dimensional cross-section of the eye and its orbit.
- A B-scan is generally used to evaluate diseases involving the posterior segment (the hind two-third of the eye) and orbit, typically when the ocular media (fluids within the eye) are cloudy and a direct visualization is not possible.
- They may diagnose eye ailments such as
- vitreous hemorrhage,
- retinal detachment,
- eye cancers, and
- foreign bodies in the eye.
How do A-scan and B-scan work?
- A-scan and B-scan techniques are based on the principles of ultrasonography. Sound travels in a wave pattern. For a sound to be heard by the human ear, the frequency must be between 20 and 20,000 Hz (20 kHz).
- Ultrasound uses a sound of frequency of more than 20 kHz. When the sound of this frequency comes in contact with an object, it bounces back. These “echoes” then touch the ultrasound probe.
- The probe converts the energy of the sound into an electrical signal that can then be interpreted as an image on a monitor.
- The doctor or sonologist will use ultrasounds of different frequencies to control the depth of the image depending upon the structures to be examined.
- For an eye examination through A-scan and B-scan, an ultrasound of frequency of around 10 MHz is used.
What happens during A-scan and B-scan?
A-scan and B-scan are safe and painless procedures.
- During an A-scan, the doctor will put anesthetic drops in your eyes to make them numb. You will be asked to sit in a chair and place your chin on a chin rest. The doctor will then ask you to look straight ahead. They will place an ultrasound wand (a device that produces ultrasound waves that bounce off eye tissues and make echoes) on the front surface of the eye.
- During a B-scan, the doctor will ask you to close your eyes. A gel will be applied to the eyelids before using the probe. The doctor may ask you to move your eyes in multiple directions.
Both the tests are generally quick and cause minimal discomfort. Because an A-scan uses anesthetic eye drops, you must be careful about touching the eyes until the numbness subsides to avoid any injury.
Health Solutions From Our Sponsors
Medically Reviewed on 1/29/2021
References
https://emedicine.medscape.com/article/1228865-overview
https://emedicine.medscape.com/article/1228447-overview#a2
https://emedicine.medscape.com/article/1228447-overview#a2
Complete List
Top What Is the Difference Between AScan and BScan Related Articles
Eye Problems and Diabetes
Diabetes and eye problems are generally caused by high blood sugar levels over an extended period of time. Types of eye problems in a person with diabetes include glaucoma, cataracts, and retinopathy. Examples of symptoms include blurred vision, headaches, eye aches, pain, halos around lights, loss of vision, watering eyes. Treatment for eye problems in people with diabetes depend on the type of eye problem. Prevention of eye problems include reducing blood pressure, cholesterol levels, quitting smoking, and maintaining proper blood glucose levels.
Dry Eye Quiz
What causes dry eye? Take this quiz to learn about dry eye syndrome and what can be done about it.
Eye Allergy
Eye allergy (or allergic eye disease) are typically associated with hay fever and atopic dermatitis. Medications and cosmetics may cause eye allergies. Allergic eye conditions include allergic conjunctivitis, conjunctivitis with atopic dermatitis, vernal keratoconjunctivitis, and giant papillary conjunctivitis. Dry eye, tear-duct obstruction, and conjunctivitis due to infection are frequently confused with eye allergies. Eye allergies may be treated with topical antihistamines, decongestants, topical mast-cell stabilizers, topical anti-inflammatory drugs, systemic medications, and allergy shots.
Eye Anatomy Detail Picture
The eye has a number of components which include but are not limited to the cornea, iris, pupil, lens, retina, macula, optic nerve, choroid and vitreous. See a picture of Eye Anatomy Detail and learn more about the health topic.
Eye Care and Eye Disorder
Many common eye disorders resolve without treatment and some may be managed with over-the-counter (OTC) products. It's important to visit a physician or ophthalmologist is the problem involves the eyeball itself or the condition hasn't improved after 72 hours of use of an eye-care OTC product.
Common Eye Problems
Eye diseases can cause damage and blindness if not treated soon enough. Learn the warning signs and symptoms of common eye conditions such as glaucoma, cataracts, pink eye, macular degeneration and more.
What Are Eye Floaters?
Eye floaters are deposits or condensation that forms in the eye's vitreous humor. These deposits cast shadows on the retina, and as the eye moves, the deposits shift position, making it appear as though the shadows are moving or floating.
Eye Strain
Eye strain is a symptom caused by looking at something for a long time. Symptoms and signs include redness, light sensitivity, headaches, and blurred vision. Symptoms may be treated by closing the eyes and taking a break from the visual task.
Eye Conditions Quiz
What do you know about your eyes? Take this quick quiz to learn about a range of eye diseases and conditions.
Eyewear Slideshow
Learn about your eye care needs and fashion wishes -- with eye glasses, frames and eyewear for computer use, reading, driving, sports and more.
Eye Herpes
Herpes of the eye occurs due to herpes simplex virus-1 (HSV-1). Symptoms of herpes of the eye include pain in and around the eye, rash or sores on the eyelids, redness, swelling, and cloudiness of the cornea.
How Can I Get My Eye To Stop Twitching?
A blepharospasm (eye twitch) is a harmless, involuntary spasm of the muscle of the eyelids, which may resolve on its own. If the twitching isn't caused by an underlying condition, getting more rest and avoiding alcohol and caffeine may help stop it.
Is Pinkeye Contagious?
Pinkeye (conjunctivitis) is inflammation of the conjunctiva. Whether pinkeye is contagious depends upon what is causing the irritation. With pinkeye, people may experience swollen eyelids, a pinkish color in the whites of the eyes, eye discharge, photophobia, increased tear production, and itching.
Laser Eye Surgery
How does LASIK work? Get information on this popular laser eye surgery, the procedure, success rates, and possible vision side effects from LASIK eye surgery.
Pink Eye (Conjunctivitis): Types, Treatment, and Symptoms
Pinkeye, also called conjunctivitis, is redness or irritation of the conjunctivae, the membranes on the inner part of the eyelids and the membranes covering the whites of the eyes. These membranes react to a wide range of bacteria, viruses, allergy-provoking agents, irritants, and toxic agents.
Pink Eye Slideshow
How do you get pink eye? And how contagious is pinkeye? If you woke up with crusty eyelids and red, swollen eyes, you may have conjunctivitis. Learn about eye drops and home remedies for pink eye.
When Should I Be Worried About Eye Twitching?
An eye/eyelid twitch (myokymia), is an involuntary, repeated spasm of the eyelid muscle. It can happen in the upper or lower lids. Eye twitching is usually painless and harmless. It often resolves without treatment. Though less common, eye twitching is sometimes the first sign of a chronic movement disorder.