The gain control is similar to the volume control on a radio. This allows for the best combination of tissue penetration and image resolution.Īnother important aspect of all ultrasound instruments is the ability to adjust the amplification of echo signals. Ophthalmic ultrasound most commonly uses a frequency of 10MHz. The soundwaves used are inaudible to human ears because they have a frequency greater than 20KHz.
This process is repeated 1,000 times per second to produce a real-time display. The stronger the echo, the brighter the display. This signal is then reconstructed into a two-dimensional image on a monitor. As these soundwaves strike the intraocular structures, an echo is reflected back to the probe and converted into an electrical signal. Click image to enlarge.ī-scan ultrasound uses high frequency soundwaves that are transmitted from a probe/transducer into the eye. The top of this scan is the 12 o’clock position, the middle is the 3 o’clock position and the bottom is the 9 o’clock position. It can also be a powerful diagnostic tool even when pathology is clinically visible ( Table 1). It can be done safely on adults and children. B-scan ultrasonography is a painless, noninvasive method that can be performed easily in the clinic, or at a hospital bedside.
It is capable of providing valuable information about the lens, vitreous, retina, choroid, sclera and orbit. The patient looks nasally while the probe is placed at the 9 o’clock position with the probe marker oriented at 12 o’clock. This patient is undergoing a transverse 3 o’clock scan. Ultrasound has been used in eye care since the 1950s for accurately imaging the internal ocular structures when this information is not obtainable by other methods ( Table 1). In these cases, the best tool at our disposal is B-scan ultrasonography. What is an optometrist to do when a patient has a condition that prevents you from examining the internal structures of the eye? We’ve all had patients with opaque corneas, dense cataracts or vitreous hemorrhages that completely or partially obscure our view of the posterior segment by conventional slit-lamp examination or biomicroscopy.
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