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Ultrasound
Ultrasound utilizes sound waves to form an
image of the eye. It works in a very similar manner that sonar is used to
"view" the ocean floor. High frequency sound waves (out of the
range of the human ear) are emitted from a probe. The sound waves travel
through eye, reflect from ocular structures back to the transducer inside the
probe. The transducer receives the sound waves and converts them into the
image that appears on the examiner's screen.
Ophthalmic ultrasound is used to measure the
parts of the eye, document pathology such as tumors, and examine inside the
eye. The sound frequency emitted from the probe determines the type of
image formed on the screen.
The two most common types of ultrasound used in
ophthalmology are A-Scans and B-Scans.
A-Scan
A-Scan is a one-dimensional display of sound
waves. Each time a sound wave hits a structure in the eye, a spike is
formed on the examiner's screen. The height and spacing between each of
the echoes provides the examiner with valuable information. A-Scans are
most commonly used to measure the eye length to determine the appropriate
intraocular lens for cataract surgery.
B-Scan
B-Scan is used to create a two-dimensional,
cross-section view of the eye. Multiple sound waves are emitted from the
probe allowing the examiner to visualize structures within the
eye.
This instrument is extremely valuable when the doctor's view inside the eye is obstructed by blood, an extremely dense cataract, or other cloudy media.
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