What Is the Difference Between A-Scan and B-Scan?
Ultrasound ophthalmology special diagnostic instrument is a special ophthalmology device used for the diagnosis of intraocular diseases, the measurement of ocular biological structure parameters and the numerical calculation and design of intraocular lenses, also known as ophthalmology AB ultrasound.
The application of ophthalmology A-ultrasound in ophthalmological ultrasound diagnosis is to use the principle of ultrasonic distance measurement, which calculates the distance by measuring the time interval of the reflected waves at the interface of different tissues of the eyeball.
Usually can be divided into:
1. Axial length measurement: usually use about 10MHz A-ultrasound probe to identify the strong reflection of ultrasound at the tissue interface between the anterior chamber, lens, vitreous and retina, and measure the transmission time of ultrasound in different tissues, and then according to the speed of sound of different tissues Calculate the distance of each segment and obtain the eye axis length AL. Ophthalmology A-ultrasound probes usually use direct contact method or water bath method for measurement. When direct contact method is used, the contact part of the probe is cornea (mucosal contact). When using water bath method, an eye cup is required.
2. Corneal thickness measurement: Usually a 15MHz-20MHz corneal thickness probe is used to measure the time interval of the ultrasonic wave reflected at the front and back interfaces of the cornea, and then calculate the corneal thickness based on the speed of sound of the cornea.
The basic principle of ophthalmology B-ultrasound imaging is the same as that of general-purpose B-mode ultrasound diagnostic equipment. According to its anticipated needs for intraocular and orbital tissue structure inspection, a high-frequency probe of 10MHz-25MHz is usually used, and its geometrical size and acoustic window structure should be suitable for the structure of the human eye. The 0-13MHz ophthalmic B-ultrasound probe is used for imaging of intraocular and orbital tissues. The 13-25MHz ophthalmic B-ultrasound probe is usually used to improve the ability of scanning and distinguishing retinal tissue structure. The probe usually directly contacts the eyelid skin to image the eyeball and orbit
What Is the Difference Between A-Scan and B-Scan?
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.
