Ultrasound
OVERVIEW
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. An 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-Scans are used to create two-dimensional, cross-section views 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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