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B-Scan Ocular Ultrasound

  • Author: Rhonda G Waldron, MMSc, COMT, CRA, ROUB, CDOS; Chief Editor: Timothy Jang, MD  more...
 
Updated: May 09, 2016
 

Overview

B-scan ultrasonography is an important adjuvant for the clinical assessment of various ocular and orbital diseases. With understanding of the indications for ultrasonography and proper examination technique, one can gather a vast amount of information not possible with clinical examination alone. This article is designed to describe the principles, techniques, and indications for echographic examination, as well as to provide a general understanding of echographic characteristics of various ocular pathologies.[1]  

 

See Eye Globe Anatomy and Extraocular Muscle Anatomy for information about the relevant anatomy.

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Indications for Examination

B-scan ultrasound is most useful when direct visualization of intraocular structures is difficult or impossible. Situations that prevent normal examination include lid problems (eg, severe edema, partial or total tarsorrhaphy), keratoprosthesis, corneal opacities (eg, scars, severe edema), hyphema, hypopyon, miosis, pupillary membranes, dense cataracts, or vitreous opacities (eg, hemorrhage, inflammatory debris).[2]

In such cases, diagnostic B-scan ultrasound can accurately image intraocular structures and give valuable information on the status of the lens, vitreous, retina, choroid, and sclera. However, in many instances, ultrasound is used for diagnostic purposes even though pathology is clinically visible. Such instances include differentiating iris or ciliary body lesions; ruling out ciliary body detachments; and differentiating intraocular tumors, serous versus hemorrhagic choroidal detachments, rhegmatogenous versus exudative retinal detachments, and disc drusen versus papilledema.

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Ultrasound Principles and Physics

Ophthalmic ultrasonography uses high-frequency sound waves, which are transmitted from a probe into the eye. As the sound waves strike intraocular structures, they are reflected back to the probe and converted into an electric signal. The signal is subsequently reconstructed as an image on a monitor, which can be used to make a dynamic evaluation of the eye or can be photographed to document pathology.

Sound is emitted in a parallel, longitudinal wave pattern, similar to that of light. The frequency of the sound wave is the number of cycles, or oscillations, per second, measured in hertz (Hz). For sound to be considered ultrasound, it must have a frequency of greater than 20,000 oscillations per second, or 20 KHz, rendering it inaudible to human ears.[3] The higher the frequency of the ultrasound, the shorter the wavelength (distance from the peak of one wave to the peak of the next wave). A direct relationship exists between wavelength and depth of tissue penetration (the shorter the wavelength, the more shallow the penetration). However, as the wavelength shortens, the image resolution improves.

Given that ophthalmic examinations require little in the way of tissue penetration (an eye being 23.5 mm long on average) and much in the way of tissue resolution, ultrasound probes used for ophthalmic B-scan are manufactured with very high frequencies of about 10 million oscillations per second, or 10 MHz. In contrast, ultrasound probes used for purposes such as obstetrics use lower frequencies for deeper penetration into the body, and, because the structures being imaged are larger, they do not require the same degree of resolution. Recently, high-resolution ophthalmic B-scan probes (ultrasound biomicroscopy or UBM) of 20-50 MHz have been manufactured that penetrate only about 5-10 mm into the eye for incredibly detailed resolution of the anterior segment.[4]

Velocity

The velocity of the sound wave is dependent on the density of the medium through which the sound travels. Sound travels faster through solids than liquids, an important principle to understand since the eye is composed of both. There are known velocities of different components of the eye, with sound traveling through both aqueous and vitreous at a speed of 1,532 meters/second (m/s) and through the cornea and lens at an average speed of 1,641 m/s.[3]

Reflectivity

When sound travels from one medium to another medium of different density, part of the sound is reflected from the interface between those media back into the probe. This is known as an echo; the greater the density difference at that interface, the stronger the echo, or the higher the reflectivity.[3]

In A-scan ultrasonography, a thin, parallel sound beam is emitted, which passes through the eye and images one small axis of tissue; the echoes of which are represented as spikes arising from a baseline. The stronger the echo, the higher the spike. For example, the vitreous is less dense than the vitreous hyaloid, which, in turn, is much less dense than the retina. Therefore, the spike obtained as the sound strikes the interface of the vitreous and hyaloid is shorter than the spike obtained when the sound strikes the hyaloid-retinal interface.

A-scan image of an eye with a traumatic vitreous h A-scan image of an eye with a traumatic vitreous hemorrhage, posterior vitreous detachment layered with blood, and peripheral choroidal detachment. A thin, parallel sound beam passes through the eye, imaging one small point through the tissues as it passes. The echoes returned to the probe in A-scan mode (left) are converted to spikes that arise from baseline, the amplitude of which is determined by the strength of the echo, giving the examiner information regarding the density of the tissues.

In B-scan ultrasonography, an oscillating sound beam is emitted, passing through the eye and imaging a slice of tissue; the echoes of which are represented as a multitude of dots that together form an image on the screen (see Image 2). The stronger the echo, the brighter the dot. Using the same example, the dots that form the posterior vitreous hyaloid membrane are not as bright as the dots that form the retinal membrane. This is very useful in differentiating a posterior vitreous detachment (a benign condition) from a more highly reflective retinal detachment (a blinding condition).

See the image below.

B-scan image of the same traumatic vitreous hemorr B-scan image of the same traumatic vitreous hemorrhage, posterior vitreous detachment, and low-lying choroidal detachment. An oscillating sound beam passes through the eye, displaying a slice of tissue in one image. The echoes returned to the probe are displayed as a series of dots that form an image, the brightness of which is determined by the strength of the echo, allowing the examiner to determine the density of the tissue for diagnostic purposes.

Angle of incidence

The angle of incidence of the probe is critical for both A-scan and B-scan ultrasonography. When the probe is held perpendicular to the area of interest, more of the echo is reflected directly back into the probe tip and sent to the display screen. When held oblique to the area imaged, part of the echo is reflected away from the probe tip and less is sent to the display screen.[3] The more oblique the probe is held from the area of interest, the weaker the returning echo and, thus, the more compromised the displayed image.

On A-scan, the greater the perpendicularity, the more steeply rising the spike is from baseline and the higher the spike. On B-scan, the greater the perpendicularity, the brighter the dots on the surface of the area of interest. The size and shape of the surface at each interface also affect that reflection. When a surface is large and flat and the probe is held in a perpendicular manner, the complete echo returns to the probe for display. If the surface is curved or irregular in shape, part of the echo is reflected away and less echo returns to the probe for display, even when the probe is held in a perpendicular manner. If the interface is very small, as in a vitreous opacity, so much of the sound is scattered that the returning echo is very weak.

Because various parts of the eye and various pathologies are different in size and shape, understanding this concept and anticipating the best possible display for that eye are important. Perpendicularity to the area of interest should be maintained to achieve the strongest echo possible for that structure.

Absorption

Ultrasound is absorbed by every medium through which it passes. The more dense the medium, the greater the amount of absorption.[3] This means that the density of the solid lid structure results in absorption of part of the sound wave when B-scan is performed through the closed eye, thereby compromising the image of the posterior segment. Therefore, B-scan should be performed on the open eye unless the patient is a small child or has an open wound. By performing on the open eye, the patient is also now able to look in extreme down gaze, which is impossible when the eye is closed and rotated upward. Because the probe is placed directly on the conjunctiva, and because the probe face and the globe must not be separated by any air, a liberal amount of gel-type tear solution should be placed on the probe face prior to examination. Care should be taken that only those solutions designed for ophthalmic use are incorporated so that eye irritation does not occur.

Likewise, when performing an ultrasound through a dense cataract as opposed to the normal crystalline lens, more of the sound is absorbed by the dense cataractous lens and less is able to pass through to the next medium, resulting in weaker echoes and images on both A-scan and B-scan. For this reason, the best images of the posterior segment are obtained when the probe is in contact with the conjunctiva rather than the corneal surface, bypassing the crystalline lens or intraocular lens implant. Finally, when calcification of tissue is present, there is so much absorption and such a strong reflection of the echo back to the probe that there is no signal posterior to that medium. This is referred to as shadowing.

See the image below.

Shadowing caused from sound absorption by the calc Shadowing caused from sound absorption by the calcium within a choroidal osteoma. Calcium is so dense that no sound can penetrate it to travel on to the next structure.
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Instrumentation

Ophthalmic ultrasound instruments use what is known as a pulse-echo system, which consists of a series of emitted pulses of sound, each followed by a brief pause (microseconds) for the receiving of echoes and processing to the display screen. The amplification of the display can be altered by adjusting the gain, which is measured in decibels (dB). Adjusting the gain in no way changes the frequency or velocity of the sound wave but acts to change the sensitivity of the instrument's display screen. When the gain is high, weaker signals are displayed, such as vitreous opacities and posterior vitreous detachments. When the gain is low, the weaker signals disappear, and only the stronger echoes, such as the retina, remain on the screen. However, there is better resolution, or detail, of the area of interest when the gain is lowered. Typically, all examinations begin on highest gain so that no weak signals are missed; then, the gain is reduced as necessary for good resolution of the stronger signals.[3]

Sterile dry eye gel should be dispensed onto the surface of the probe face, which is usually oval in shape and when placed on the anesthetized globe, is represented by the initial white line on the left side of the display screen. The vitreous cavity is displayed in the center of the echogram, and the posterior pole is displayed on the right side of the echogram. There is a marker (usually a dot or line) on the side of the probe handle near its face, on one side of the short end of the oval. Knowing the orientation of the marker at all times is extremely important because it represents the upper portion of the echogram. The back-and-forth motion of the transducer occurs along the long portion of the oval; thus, the slice emitted occurs in the direction of the marker.

In other words, if the area of interest is at the 3-o'clock position, the probe face is held on the globe at the 9-o'clock position with the marker aimed upward. The center of the probe is aiming at the 3-o'clock position, which appears in the center of right side of the echogram, the area of best resolution. The top of the right side of the echogram represents the 12-o'clock position since that is the orientation of the marker, and the bottom of the echogram on the right represents the 6-o'clock position since that is the portion opposite the marker. Therefore, the slice of tissue on the right side of the display is from the 12-o'clock position to the 6-o'clock position, with the 3-o'clock position in the center. If the probe is held at the 9-o'clock position but rotated so the marker is now aimed inferiorly, the 3-o'clock position remains in the center of the display, but now the 6-o'clock position is at the top and the 12-o'clock position is at the bottom.

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Probe Positioning

Transverse probe positions

The transverse probe position most commonly is used. This technique demonstrates the lateral extent of the pathology and encompasses approximately 6 clock hours.[3] Because of the area covered, this orientation is used for basic screening examinations when there is no view of the posterior segment. See the image below.

Transverse scan of a choroidal melanoma. This is a Transverse scan of a choroidal melanoma. This is a lateral slice through the lesion centered at the 5:00 position left eye, with 3 clock hours represented both above (2:00, 3:00, and 4:00 positions, respectively, from the top) and below (6:00, 7:00, and 8:00 positions) the lesion.

With the eye anesthetized, the patient should be instructed to look in the direction of the area of interest. The probe face is coated in gel-type tear solution and positioned on the opposite conjunctival surface parallel to the limbus, regardless of probe location around the globe, with the marker aimed either superiorly or nasally. Consequently, the marker is oriented superiorly when examining the nasal or temporal globe (3-o'clock or 9-o'clock positions) and toward the nose when examining the superior or inferior globe (12-o'clock or 6-o'clock positions). When the probe is aimed at an oblique clock hour, such as 10:30 or 5:00, the marker should be oriented in the superior portion of the oblique angle.

Knowing the position of both the probe face and the marker in relation to the patient's gaze is critical to understanding the position and orientation of pathology within the eye. By knowing these, what lies in the center, top, and bottom on the right side of the echogram, and all meridians in between, is understood. For example, if scanning the superior portion of the right globe, the patient looks upward, and the probe is placed on the conjunctiva at the 6-o'clock position, with the marker aimed toward the nose at the 3-o'clock position. The cross section of the eye seen on the display screen corresponds to the following aspects of the globe: the 12-o'clock position will be centered on the right side of the echogram, the 3-o'clock position will be at the top, and the 9-o'clock position will be at the bottom. Thus, the clock hours represented are the 3-o'clock, 2-o'clock, 1-o'clock, 12-o'clock, 11-o'clock, 10-o'clock, and 9-o'clock positions, respectively, from top to bottom on the right side.

For oblique positions, such as the 1:30 position in the left eye, the patient should be instructed to look up and left. The probe is held on the opposite conjunctiva (inferonasal) with the marker oriented superiorly in the oblique angle. Thus, from the top of the display to the bottom, the clock hours represented are the 10:30, 11:30, 12:30, 1:30, 2:30, 3:30, and 4:30 positions, respectively. Any clock hour can be centered easily, and, by adding and subtracting about 3 clock hours, all of the clock hours represented can be estimated. The designation of each transverse scan is by that clock hour in the center on the right side, followed by an estimation of how far in the periphery the slice is at that clock hour. The labeling system for this estimation is as follows: P for posterior pole, PE for posterior/equator, EP for equator/posterior, E for equator, EA for anterior to the equator, O for ora serrata, and CB for ciliary body.[3]

A limbus-to-fornix approach is a technique used to examine each meridian from the posterior pole to the periphery. The probe is swept from the limbus to the fornix as far as possible, pivoting on axis to follow the curvature of the globe. When the probe is placed at the limbus, the sound beam slice is aimed at the posterior pole. When brought toward the fornix, the slice is now aimed more peripherally, and the further it can be moved into the fornix, the more anterior the scan. By sweeping back-and-forth, limbus-to-fornix, in each transverse meridian, several clock hours are being examined not only at once but also from the posterior pole out to the anterior portion of the globe.

Longitudinal probe positions

Whereas transverse probe positions demonstrate the lateral extent of pathology, longitudinal probe positions represent the radial extent. Longitudinal scans demonstrate only 1 clock hour per echogram radially, but that clock hour is represented from the posterior pole out to the anterior equator or ora serrata.[3]

See the image below.

Longitudinal scan of the same choroidal melanoma. Longitudinal scan of the same choroidal melanoma. This is a radial slice through the lesion, with 1 clock hour (in this case, the 5:00 position) being represented from the optic nerve and posterior pole (at the bottom of the right side) outward to the anterior meridian.

This technique is an adjuvant to the transverse probe examination in many situations but most importantly for intraocular tumors and retinal tears. The transverse probe position assesses the lateral width of an intraocular tumor, whereas the longitudinal probe position evaluates the radial extent and the proximity to the optic nerve. Because the flap of a retinal tear is directed radially toward the posterior pole from the periphery, a longitudinal scan is the only way to image the flap. If only transverse cuts are used, a retinal tear can easily remain undetected and therefore untreated, resulting in subsequent retinal detachment. When a tumor is being measured, the height can be measured on either a transverse scan or a longitudinal scan, but the width of the lesion must be measured in both the lateral direction and the radial direction so that the largest width can be detected for treatment (eg, determining radiation plaque size).

As with transverse scans, the patient is instructed to look in the direction of the area of interest, and the probe face is placed on the opposite conjunctival surface. However, in longitudinal scanning, the probe face is rotated so that it is perpendicular to the limbus, with the marker directed toward the limbus, or toward the area of interest, regardless of the clock hour being examined. This results in the optic nerve shadow being represented at the bottom on the right side of each longitudinal echogram, and the posterior pole just above the nerve shadow. The anterior portion of the clock hour is represented at the top of the right side. The designation of the longitudinal scan is simply the clock hour being examined followed by an "L."

A limbus-to-fornix approach should be used in longitudinal scanning to adequately center the pathology into the area of best resolution. For instance, if the pathology is located near the posterior pole, by placing the probe near the limbus, that area will be centered. However, if the pathology is located in the far periphery, the probe will need to be shifted farther into the fornix to achieve adequate centration. The nerve shadow will shift downward, and, depending on how far into the fornix the shift, the shadow may be moved so far inferiorly that it is no longer visible on the display screen.

Axial probe positions

The term axial probe position as used in B-scan echography is different in meaning to the term axial as used in A-scan biometry. In biometry, this term is used for the measurement of the length of the eye along the visual axis, or through the vertex of the cornea, center of the lens, and the center of the macula.

In B-scan echography, the term axial refers to the centering of the posterior lens curve to the left of the echogram and the optic nerve shadow to the right of the echogram rather than the macula.[3]

See the image below.

Axial scan of the same melanoma. The posterior len Axial scan of the same melanoma. The posterior lens surface is seen centrally to the left of the scan, and the optic nerve shadow is seen centrally on the right. Because the lesion is situated below midline, the marker is directed opposite the lesion, or at the 11:00 position, with the 5:00 position lesion displayed inferior to the nerve, and the 11:00 position displayed above the nerve.

To accomplish this, the patient must be looking in primary gaze, and the probe should be centered on the corneal vertex. Because the probe is being placed on the cornea rather than the conjunctiva, additional gel-type solution should be used for cushioning to protect the corneal surface. Because the optic nerve inserts into the globe just nasal to the macula, the probe should be tilted to aim the sound beam slightly nasally to image the nerve in the right center of the echogram. The orientation of the marker depends on the desired meridian. Because the ultrasound slice is emitted from the probe tip in the direction of the longest oval of the probe face along the line of the marker, any clock hour can be imaged in the upper and lower quadrants of the right side by changing marker orientation.

Note that because the sound is now traveling through the lens, some absorption will occur, compromising the fundus image. If an intraocular lens is present on axial scanning, artifact reverberations will occur in the vitreous cavity, as with A-scan biometry.

A horizontal axial scan is accomplished by rotating the marker to aim toward the nose, or the 3-o'clock position for the right eye or the 9-o'clock position for the left eye. This results in the slice cutting through the nerve horizontally, with the nasal meridian (ie, 3-o'clock position right eye, 9-o'clock position left eye) at the top of the right side, and the temporal meridian (ie, 9-o'clock position right eye, 3-o'clock position left eye) at the bottom. This is the most useful axial scan for basic screening purposes because the nerve and macula are both in the display. Because the macula is located just temporal to the optic nerve, the macula is located just inferior to the nerve shadow on the echogram.

A vertical axial scan is produced by rotating the marker superiorly toward the 12-o'clock position in either eye. The slice will now cut through the nerve vertically with the 12-o'clock position at the top on the right and the 6-o'clock position at the bottom in either the right or left eye.

For oblique axial scans, the marker is rotated to include the clock hours desired. By convention, if the meridian desired is located above midline, the marker should be directed toward that meridian. If the meridian desired is located below midline, the marker should be oriented opposite that meridian. For example, if the desired meridian is a tumor at the 11-o'clock position, rotate the marker toward the 11-o'clock position, and the tumor will appear in the upper-right of the scan, with the 5-o'clock position at the bottom, below the nerve. However, if the tumor resides at the 5-o'clock position, the marker should be rotated toward the 11-o'clock position, and the 11-o'clock position will appear at the top-right of the scan, with the 5-o'clock position tumor below the nerve, at the bottom.

See the image below.

Axial scan of the same melanoma. The posterior len Axial scan of the same melanoma. The posterior lens surface is seen centrally to the left of the scan, and the optic nerve shadow is seen centrally on the right. Because the lesion is situated below midline, the marker is directed opposite the lesion, or at the 11:00 position, with the 5:00 position lesion displayed inferior to the nerve, and the 11:00 position displayed above the nerve.
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Basic Screening Technique

Basic screening refers to an examination performed when there is no view into the eye because of opaque media, such as corneal edema or scarring, extremely dense cataracts, or vitreous hemorrhages, and the determination of the status of the posterior segment is required. In these cases, the highest gain setting must be used to visualize any weak signals, such as vitreous opacities and posterior vitreous detachments, or to gauge the extent of vitreous hemorrhages. If any pathology such as retinal or choroidal detachments is found, then the gain may be reduced for better resolution of the stronger signals from these structures once the basic screening is completed and documented.

Technique

During basic screening, the entire globe must be examined, from the posterior pole out to the far periphery. Using a limbus-to-fornix approach, each quadrant is evaluated carefully.[3] The 4 major quadrants include the 12-o'clock, 3-o'clock, 6-o'clock, and 9-o'clock positions, each centered on the right side of the echogram in transverse approaches. Because approximately 6 clock hours are imaged at once, by examining each quadrant, the areas examined will overlap, thereby reassuring the examiner that the entire periphery of the globe is visualized. A photo or printed documentation of each of the 4 quadrants should be obtained. Next, document the posterior pole with a horizontal axial scan, which incorporates both the optic nerve and the macula in one echogram. If no additional pathology is detected, these 5 echograms complete the examination.

Centering pathology found during basic screening

If any posterior pathology is detected during basic screening, it should be centered on the right side of the echogram to achieve greatest resolution. This is accomplished by determining the clock hour represented in the center, top, and bottom of the right side on the transverse scan where it was discovered, and then determining where this pathology lies in relation to those clock hours. Once determined, the patient should be instructed to redirect his or her gaze to that meridian, with the probe then placed on the opposite scleral surface. Perpendicularity to the pathology is achieved when it is centered and when the vertex of the pathology is a brighter white. The gain is now reduced until the greatest resolution is achieved, and photographic documentation is produced with proper labeling.

Additional scans may be required, such as longitudinal scans to document the radial aspect of the pathology, axial scans to document location of the pathology from the optic disc, and diagnostic A-scans for tissue differentiation.

Localization of the macula

The 4 methods of localizing and centering of the macula are as follows: horizontal, vertical, transverse, and longitudinal. Depending on the eye, one method may be preferable to another, or a combination of methods may be desired.

The horizontal method involves placing the probe on the corneal vertex with the marker nasally, as with a horizontal axial scan; but, rather than tilting to center the nerve, the probe should be aimed straight ahead to center the macula. The nerve shadow will now shift upward slightly, and the macula will be centered to the right of the echogram, with the posterior lens surface centered to the left. These scans should be labeled HMAC.[3]

See the image below.

Horizontal macula scan in an eye with a vitreous h Horizontal macula scan in an eye with a vitreous hemorrhage. The posterior lens surface is seen centered to the left, with the macula centered to the right. The optic nerve is seen just above the macula, since the marker is directed nasally.

The vertical method involves again placing the probe on the corneal vertex, but the marker is in the 12-o'clock position. Rather than tilting to center the optic nerve, as with a vertical axial scan, the probe should be aimed straight back to center the macula. The nerve will not appear in these scans because this is a vertical (instead of horizontal) slice of the macula. These scans should be labeled VMAC.[3]

See the image below.

Vertical macula scan of an eye with a mild vitreou Vertical macula scan of an eye with a mild vitreous hemorrhage and a submacular hemorrhage. The posterior lens surface is centered to the left, with the macula centered to the right. Because the slice is vertical through the visual axis, the optic nerve shadow is not displayed.

The transverse method involves the patient fixating slightly temporally and placing the probe onto the nasal sclera with the marker at the 12-o'clock position. Using the optic nerve as the center of the imagined clock, the macula is at the 9-o'clock position at the posterior pole in the right eye and at the 3-o'clock position at the posterior pole in the left eye. This scan bypasses the lens, thereby preventing absorption or reverberation artifacts from an intraocular lens. These scans should be labeled TMAC.[3]

See the image below.

Transverse macula scan of an eye with macular edem Transverse macula scan of an eye with macular edema. This is also a vertical scan through the macula, so the optic nerve is not seen. Because the probe is held on the sclera rather than the cornea, the crystalline lens is bypassed and not imaged to the left.

The longitudinal method also bypasses the lens. This method involves directing the patient's gaze slightly temporally, with the probe on the nasal sclera and the marker oriented toward the limbus or temporally toward the macula. This is a horizontal scan of the macula, with the nerve at the bottom-right of the echogram and the macula just superior to the nerve, with the lateral rectus muscle visible coursing through the orbit. These scans should be labeled LMAC.[3]

See the image below.

Longitudinal macula scan in an eye with macular ed Longitudinal macula scan in an eye with macular edema. The optic nerve shadow is seen at the bottom of the right side of the scan, with the macula just above. The probe is held on the sclera rather than the cornea, therefore bypassing the crystalline lens. The lateral rectus muscle is seen in the orbit.

Because both the nerve and the macula are imaged, the longitudinal method may be preferable if the patient has a cataract or intraocular lens in place; in this orientation, the lens is bypassed while still producing an image with both the optic nerve and the macula in one echogram.

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Anterior Segment Evaluation

Immersion technique

Because the area of best resolution is in the center on the right side of an echogram, examining the anterior segment with a standard 10 MHz contract probe can be accomplished only with the use of a scleral shell. This shifts the anterior segment to the right and into the area of focus of the sound beam, improving resolution of anterior segment pathology. The shell is filled with methylcellulose or some other viscous solution to a meniscus, avoiding air bubbles within the shell. The probe is placed on top of the shell. This produces an echolucent area on the left side of the echogram corresponding to the shell and methylcellulose, and it shifts the anterior segment to the right side of the display screen.[5]

See the image below.

Immersion B-scan image of an iris melanoma extendi Immersion B-scan image of an iris melanoma extending into the ciliary body. To the left side of the scan is the scleral shell filled with methylcellulose, with the cornea and iris seen centrally and the posterior segment seen on the right.

With contact B-scan, the patient looks toward the pathology, and the probe is held opposite to adequately center the pathology, whereas with immersion B-scan, the patient looks opposite the pathology to center the area of interest directly under the shell. Diagnostic A-scan also can be performed through the shell, directly over the lesion, for tissue differentiation.

High-resolution technique

High-resolution B-scan probes have been developed for higher quality imaging of the anterior segment and have proven to be useful for many pathologies, including lesions of the iris and ciliary body, sulcus-to-sulcus measurements, angle measurements, and imaging lenses. As the frequency of the sound wave increases, the resolution increases, but the depth of tissue penetration decreases. These high-resolution probes range from 20 MHz to 50 MHz, with penetration depths of about 10 mm to 5 mm, respectively; therefore, they may be used only for imaging the anterior segment of the eye. The images rendered from these probes are far superior to that of the standard immersion technique because of the higher resolution. However, the zone of focus with these high resolution transducers is quite small; thus, the examiner must adjust the depth of the transducer in the saline to obtain best image quality.

See the image below.

High-resolution B-scan images of an iris melanoma. High-resolution B-scan images of an iris melanoma. This imaging requires a separate probe, and it delivers high magnification and superior detail of the small structures of the anterior segment. On the left is a longitudinal, or radial, scan, and on the right is a transverse, or lateral, scan.

These probes may have an external oscillating transducer and can be placed in a special scleral shell, although care must be taken so that the probe never slips into the shell far enough for the transducer to come in contact with the cornea as it oscillates. Another method is to slip the probe into a balloon-type apparatus filled with distilled water to form a protective layer of water between the transducer and the patient's eye.[3] By placing a small amount of methylcellulose on the vertex of the cover for sound conduction, the tip of the cover rests on the eye directly over the pathology for imaging.

Care should again be taken not to push hard enough against the eye for the transducer to contact the eye or for the bag of water to indent the globe, particularly if scanning to measure the angle. When using these high frequencies, any membrane in front of the transducer causes a degree of sound attenuation; the best image quality is obtained with the scleral shell technique.

For both immersion and high-resolution imaging of the anterior segment, the marker is oriented as with contact scanning for transverse, longitudinal, and axial cuts of the posterior segment. The main difference is that the probe is placed directly overlying the area of interest; depending on manufacturer, the depth of the transducer must be adjusted in the water to achieve maximum focus.

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Intraocular Diseases

Vitreous

In a young healthy eye, the vitreous is relatively echolucent. However, as the eye ages, the vitreous undergoes syneresis, and low reflective vitreous opacities can be detected. A posterior vitreous separation (a benign condition of the aging eye) may occur and is represented as a mobile, fine thin, low reflective line on B-scan.[6]

See the image below.

Low reflective vitreous opacities and a posterior Low reflective vitreous opacities and a posterior vitreous detachment as seen with normal aging of the eye.

Other conditions or diseases of the vitreous that can be detected with ultrasound include asteroid hyalosis, another benign condition of the vitreous where calcium salts accumulate in the vitreous cavity. The calcium is relatively dense and, therefore, produces multiple pinpoint, highly reflective vitreous opacities.

See the image below.

Asteroid hyalosis. The calcium soaps in this condi Asteroid hyalosis. The calcium soaps in this condition cause the dots within the vitreous cavity to be much brighter than those seen with vitreous hemorrhages.

Vitreous hemorrhage can occur in several different situations, such as after trauma or a retinal tear or as a complication of diabetes mellitus or a retinal vein occlusion. The echographic pattern of a vitreous hemorrhage depends on its age and severity. Fresh mild hemorrhages appear as small dots or linear areas of low reflective mobile vitreous opacities, whereas in more severe older hemorrhages, blood organizes and forms membranes. The membranes form large interfaces that are visualized echographically as a vitreous filled with multiple large opacities that are higher in their reflectively. Vitreous hemorrhages may also layer inferiorly due to gravitational forces.

See the image below.

Horizontal macula scan in an eye with a vitreous h Horizontal macula scan in an eye with a vitreous hemorrhage. The posterior lens surface is seen centered to the left, with the macula centered to the right. The optic nerve is seen just above the macula, since the marker is directed nasally.

Membrane formation also can occur after trauma, particularly after penetrating or perforating eye injuries. A membranous track often develops along the path of the offending object. In penetrating injuries, this track may end in the vitreous cavity or at an impact site opposite the entry site. In perforating injuries, the track spans the eye from the entry site to the exit site. Therefore, following the track may lead to an intraocular foreign body and/or retinal pathology at an impact or exit site. Intraocular foreign bodies can be detected easily with ultrasound. Even if already detected with some other imaging modality, such as computerized tomography or magnetic resonance imaging, ultrasound can more precisely localize the foreign object. This can be extremely vital information because it can determine how the surgeon approaches the case.

In a study of the reliability of ocular ultrasonography for presurgical evaluation of various vitreo-retinal conditions, including trauma, diabetic vitreous hemorrhage, endophthalmitis, and other causes of vitreous hemorrhage, overall sensitivity and specificity were 92.31% and 98.31%, respectively, for identification of rhegmatogenous retinal detachment and were 96.2% and 100%, respectively, for posterior vitreous detachment. In eyes with trauma, sensitivity was 90.9% and specificity 97.7% for identifying the status of the retina.

[6]

Retina

A retinal tear can be detected with ultrasound when using longitudinal approaches. On occasion, retinal tears are accompanied by vitreous hemorrhages, which preclude visualization of the etiologic tear. In such instances, one often can see the posterior vitreous hyaloid or a vitreous strand attached to the retinal flap. These tend to occur in the far periphery, where the vitreous is most firmly attached to the retinal surface, particularly superotemporally. A shallow cuff of subretinal fluid may accompany the tear and make the diagnosis more evident.

See the image below.

Vitreous hemorrhage with a retinal tear at the 1:3 Vitreous hemorrhage with a retinal tear at the 1:30 position. Note the vitreous hyaloid attaching to the tip of the tear. This is a longitudinal scan, which is necessary to display the tear due to the radial direction of the flap.

When a retinal detachment is present, the examiner sees a highly reflective, undulating membrane. In patients with total retinal detachments, the typically folded surface attaches to the ora serrata anteriorly and the optic nerve posteriorly. Initially, a retinal detachment is relatively mobile (with eye movement). However, with time, proliferative vitreoretinopathy (epiretinal membrane formation) can occur, and the retina becomes stiffer and takes on more of a funnel configuration.

See the image below.

Total retinal detachment and vitreous hemorrhage. Total retinal detachment and vitreous hemorrhage. The retinal detachment appears as a somewhat wavy membrane of high reflectivity in an open-funnel configuration, attaching at the optic disc and out peripherally at the ora serrata.

Retinoschisis is a condition where there is a split between specific layers of the retina. Clinically, differentiating a retinoschisis from a retinal detachment is difficult. Ultrasound can further assist in the differentiation because retinoschisis is more focal, smooth, dome-shaped, and thin.

In a study using high-resolution ultrasound B-scan to differentiate retinoschisis from retinal detachment, in the eyes with retinoschisis, the outer retina demonstrated the presence of 2 hyperreflective lines corresponding to the interfaces of the outer plexiform layer and the retinal pigment epithelium, whereas eyes with retinal detachment demonstrated 2 hyperreflective lines in the detached portion, corresponding to the nerve fiber layer and outer plexiform layer interfaces, and the attached portion demonstrated the presence of the third hyperreflective interface. These findings correlated well with spectral-domain optical coherence tomography (SD-OCT).[7]

B-scan ultrasonography commonly is used for the initial and follow-up evaluation of retinoblastoma. Retinoblastoma, a highly malignant retinal cancer found in infants and young children, commonly has focal areas of calcification within the tumor. Ultrasound can easily detect the calcium, represented as highly reflective foci within the tumor or vitreous.

See the image below.

Retinoblastoma. Note the small, highly reflective Retinoblastoma. Note the small, highly reflective echodensities within the tumor, which are foci of calcium.

When small, the tumors are smooth, dome shaped, and are low to medium in internal reflectivity. As the tumors grow, they become more irregular in configuration and more highly reflective as the amount of calcium accumulates. This pediatric cancer can be unilateral and unifocal, unilateral and multifocal, or bilateral. Ultrasound has become a very useful and very cost effective way to follow these tumors as treatment is delivered. Baseline tumor size measurements and tumor locations are obtained, and these parameters are monitored closely during and after treatment.

Typically, the presence of leukocoria (a white pupil) alerts the parent or the pediatrician to this disease. However, multiple other pediatric retinal diseases are associated with leukocoria, such as persistent hyperplastic primary vitreous (PHPV), retinopathy of prematurity (ROP), Coats disease, and medulloepithelioma. PHPV, also called persistent fetal vasculature (PFV), is almost always a unilateral condition where the primary vitreous (particularly the hyaloid vessel) fails to regress and continues to extend from the optic nerve to the posterior lens capsule. Echographically, one can detect the very thin persistent hyaloidal vessel coursing from the disc to the lens when longitudinal approaches are used. Other echographic features may include a retrolental membrane, a small globe (small axial length), and, in severe cases, an associated traction or total retinal detachment.

See the image below.

Persistent hyperplastic primary vitreous. Note the Persistent hyperplastic primary vitreous. Note the thin membrane of low reflectivity emanating from the optic disc to the posterior lens surface. A longitudinal scan is needed to image the membrane in its entirety, as opposed to a cross section transverse scan, which would demonstrate only a small, weak dot in the central vitreous cavity. Highest gain is also necessary because the membrane is a very weak signal.

ROP is a bilateral disease that may be asymmetric in its severity but is commonly quite symmetric. There are various stages of this disease; however, the most advanced stage (stage V) often has a white pupillary reflex. Stage V disease is defined as a total retinal detachment due to peripheral contraction of fibrovascular proliferative tissue and commonly has a funnel configuration. The configuration of this detachment is detected easily with ultrasound.

Coats disease is a unilateral condition characterized by retinal vascular telangiectasia and, when severe, an exudative retinal detachment. This disease can be the most difficult to differentiate from retinoblastoma. However, ultrasound is very useful because of the lack of calcium and the presence of cholesterol in the subretinal space. In the areas of telangiectasia, the retina is commonly thickened.

A medulloepithelioma is a rare tumor that primarily arises in the ciliary body of children. Typical ultrasound features include a dome-shaped configuration, high internal reflectivity, moderate vascularity, and multiple cystic spaces.

Choroid

Echographically, the choroid is much thicker than the retina. When the retina and choroid are still apposed, one can see a double spike on diagnostic A-scan, a highly reflective spike representing the vitreoretinal interface, and a slightly less reflective spike representing the retinochoroidal interface.[8] A choroidal detachment may occur spontaneously, after trauma, or following a variety of intraocular surgeries. On ultrasound, the detachment is smooth, dome-shaped, and thick. Virtually no movement is seen with eye movement. When extensive, one can see multiple dome-shaped detachments, which may "kiss" in the central vitreous cavity. When choroidal detachments are hemorrhagic rather than serous (as commonly seen in traumatic situations), the subchoroidal space is filled with a multitude of dots in contrast to the echolucent subchoroidal space of a serous choroidal detachment.

See the image below.

"Kissing" hemorrhagic choroidal detachments. The t "Kissing" hemorrhagic choroidal detachments. The thick, bullous membranes meet in the central vitreous cavity. The underlying opacity is indicative of underlying hemorrhage.

The most common tumor of the choroid is malignant melanoma. Although these can arise in the ciliary body or iris, they most commonly are seen in the choroid. Like retinoblastoma, ultrasound has become invaluable in the diagnosis and follow-up evaluation of uveal malignant melanomas. This homogenous highly cellular tumor results in low-to-medium internal reflectivity and regular internal structure.[3, 9] Diagnostic A-scan and B-scan can detect internal vascularity in most melanomas.

A nearly pathognomonic finding is a collar button configuration (ie, mushroom shape), but this shape is seen in less than 25% of cases. Histologically, the collar button represents the portion of the tumor that has broken through the Bruch membrane, a basement membrane found between the choroid and the retina.

See the image below.

Collar-button shaped choroidal melanoma. The lesio Collar-button shaped choroidal melanoma. The lesion began as a dome shape, then broke through the Bruch membrane to form the button on the anterior surface of the dome. Note the diagnostic A-scan pattern typical of melanoma, with the high retinal spike on the surface of the lesion but low-to-medium internal reflectivity within the lesion. The sclera and orbital tissues are seen as spikes to the right of the lesion.

Typically, a choroidal melanoma has a smooth, dome shape. Diffuse melanomas have a relatively flat shape and an irregular contour but maintain low-to-medium internal reflectivity.

See the image below.

Transverse scan of a choroidal melanoma. This is a Transverse scan of a choroidal melanoma. This is a lateral slice through the lesion centered at the 5:00 position left eye, with 3 clock hours represented both above (2:00, 3:00, and 4:00 positions, respectively, from the top) and below (6:00, 7:00, and 8:00 positions) the lesion.

When a portion of a melanoma outgrows its blood supply, that portion of the tumor may necrose and bleed internally, or into the subretinal, vitreous, or suprachoroidal space. If the hemorrhage is extensive, the blood may prevent echographic detection of the tumor. In such cases, follow-up examination is vital. When the tumor bleeds internally, the examiner may see highly reflective pockets within the tumor and a consequently irregular internal structure. Since larger melanomas produce significant internal sound attenuation, there is a lower reflectivity at the base of the tumor, which is referred to as acoustic hollowing.

Occasionally, choroidal evacuation is seen at the base of the tumor. This is believed to represent the tumor invading the deeper choroidal structures. A melanoma can progress further and extend through the scleral wall, referred to as extrascleral extension. This usually occurs along emissary canals. Ultrasound is probably the only reliable method of detecting small posterior extrascleral extensions.

Such information is critical to management decision making and prognosis. If a melanoma is treated with brachytherapy, intraoperative echographic localization of the plaque in relation to the tumor has significantly improved treatment success. Finally, if eye-sparing treatments can be performed, such as brachytherapy, proton beam irradiation, or transpupillary thermal therapy, ultrasound is invaluable in monitoring the tumor response in both size and internal reflectivity. A favorable response is a progressively regressing tumor with increasingly higher internal reflectivity. Obviously, an unfavorable response is a tumor that continues to grow.

Benign melanocytic tumors include nevi and melanocytomas. Like a melanoma, the pigmentation of a nevus can range from no pigmentation (amelanotic) to a deep brown pigmentation (melanotic). A melanocytoma typically is heavily pigmented. They, too, have a dome-shaped configuration but, in contrast to melanoma, are highly reflective and do not have internal vascularity. Unfortunately, small melanomas may show an absence of low internal reflectivity, and, consequently, it may be difficult to differentiate a small benign lesion from a similar sized malignant one.

Metastatic tumors can spread to the choroid due to its highly vascular nature. These tumors have a much different echographic appearance. Clinically, these tumors are creamy or yellow in color and multilobulated. Echographically, these tumors usually have an irregular lumpy contour, an irregular internal structure, a medium-to-high internal reflectivity, and little evidence of internal vascularity. Although exudative detachments occur with uveal melanomas, similar sized metastatic tumors generally have more extensive detachments. Extrascleral extension also can be seen with these tumors and, therefore, is not helpful in the differentiation of the tumor.

See the image below.

Metastatic choroidal lesion from the breast. The l Metastatic choroidal lesion from the breast. The lesion has rather irregular borders, with medium-high, irregular internal reflectivity on both B-scan and diagnostic A-scan.

Choroidal hemangioma is a benign vascular tumor of the choroid. These tumors can produce localized exudative retinal detachments and subsequent vision loss. Clinically, these tumors are orange dome-shaped tumors. Echographically, a choroidal hemangioma is dome-shaped and has a high internal reflectivity. An overlying serous retinal detachment can be seen with B-scan. A more diffuse form of a choroidal hemangioma is seen in Sturge-Weber syndrome. In these patients, the tumor is more extensive and less elevated.

See the image below.

Choroidal hemangioma with an associated exudative Choroidal hemangioma with an associated exudative retinal detachment. This lesion is composed of tightly compacted blood vessels and, therefore, demonstrates high, regular internal reflectivity on both B-scan and diagnostic A-scan.

Calcific choroidal tumors are easily differentiated and detected with B-scan. A choroidal osteoma clinically appears as a yellow lesion, commonly located near the optic nerve. These tumors are not significantly elevated. On ultrasound, they have very high internal reflectivity due to the calcium. Their contour is usually flat and smooth, but, on occasion, these tumors are lumpy in appearance. Marked shadowing occurs posterior to the tumor due to the calcium absorbing the sound energy.

See the image below.

Shadowing caused from sound absorption by the calc Shadowing caused from sound absorption by the calcium within a choroidal osteoma. Calcium is so dense that no sound can penetrate it to travel on to the next structure.

Ciliary body

The ciliary body is visualized best with high-resolution scanning; however, the immersion method may be used, or even the contact method can be used to evaluate the more posterior aspects of the ciliary body. A ciliary body detachment can extend into the peripheral choroid and can be seen on contact B-scan, although it is displayed best on high-resolution scanning. A low-to-medium reflective cleft is seen in the subciliary space.

See the image below.

Ciliary body detachment as seen on high-resolution Ciliary body detachment as seen on high-resolution scan. Note the large cleft in the subciliary space.

Ciliary body tumors are similar to those seen in the choroid. The most common ciliary body tumors are melanomas; however, a variety of other tumors do arise in the ciliary body, including metastatic tumors, medulloepitheliomas, and leiomyomas.

Sclera

Diagnostic ultrasonography is probably the best way to evaluate scleral thickening. Scleral thickening occurs in cases of nanophthalmos (very small eyes), ocular hypotony, phthisis bulbi, and scleritis. In scleritis, the degree of scleral thickening can vary from mild to severe, and it can be focal or diffuse. Commonly, associated edema adjacent to the sclera is present. This manifests itself as an echolucent area in the Tenon space. When posterior and adjacent to the optic nerve, it forms a T-sign. Other associated findings include a thickened highly reflective sclera, retinal detachments, and ciliochoroidal detachments.

See the image below.

Nodular posterior scleritis with fluid in the Teno Nodular posterior scleritis with fluid in the Tenon capsule. The scan on the right demonstrates a positive T-sign at the insertion of the optic nerve.

Patients who are myopic may have focal areas of thinning sclera. These areas can form staphylomas, or out-pouching. Ultrasound is the best imaging modality for staphylomatous changes. In trauma, occult scleral ruptures can be difficult to appreciate on clinical examination. Ultrasound typically cannot detect the actual rupture; however, several echographic clues can assist the clinician. These clues include hemorrhage in the immediate episcleral space, a thickened or detached choroid, a detached retina in the area of concern, vitreous hemorrhage, or vitreous incarcerated into the rupture.

See the image below.

Posterior staphylomas. The uvea in this patient ha Posterior staphylomas. The uvea in this patient has become so thin that it is bulging posteriorly in the macular area and just nasal to the disc.

Optic nerve

Optic disc cupping usually can be seen on clinical examination. However, if media opacities prevent examination, the contour (including the degree of cupping) can be detected with ultrasound. Similarly, optic nerve colobomas are imaged easily with ultrasound.

See the image below.

Optic nerve cup. Note the indentation to the optic Optic nerve cup. Note the indentation to the optic disc, a result of increased intraocular pressure in glaucomatous diseases.

When seen clinically, differentiating papilledema (optic disc edema) from pseudopapilledema is critical since the former is associated with elevated intracranial pressure, while the latter may have no systemic relevance. Optic disc drusen are calcific nodules buried within the optic nerve head and can simulate papilledema. On ultrasound, these nodules are highly reflective and exist at or within the optic nerve head.

See the image below.

Optic nerve head drusen. Note the highly reflectiv Optic nerve head drusen. Note the highly reflective echodensity of the calcium.

In true papilledema, increased intracranial pressure (ICP) is transmitted along the subdural space within the optic nerve. Clinical entities that can cause elevated intracranial pressure include pseudotumor cerebri and intracranial tumors. When the ICP is mildly elevated, the optic nerve is slightly widened. In the more severe cases, one can see an echolucent circle within the optic nerve sheath (separating the sheath from the optic nerve). This is the so-called crescent sign.

See the image below.

Increased subarachnoid fluid around the optic nerv Increased subarachnoid fluid around the optic nerve. Note the positive crescent sign.

The presence of increased fluid within the sheath is confirmed best with the 30-degree test, which is a dynamic A-scan test that measures the width of the optic nerve in primary gaze and again after the patient shifts gaze 30 degrees from primary. In cases of increased ICP, the nerve and sheath are stretched as the globe turns 30 degrees, and the subarachnoid fluid is distributed over the extent of the nerve, resulting in measurements less than when in primary gaze. If nerve enlargement is due to parenchymal infiltration or thickening of the optic nerve sheath, then the measurement will not change as the globe turns from primary.

An optic nerve glioma is a neoplastic process that infiltrates the optic nerve parenchyma. On ultrasound, this is a smooth, fusiform mass with low-to-medium and regular internal reflectivity. An optic nerve sheath meningioma is an example of a tumor of the optic nerve sheath. In contrast to a glioma, this neoplastic process typically has a medium-to-high, irregular internal reflectivity with possible areas of calcification.

Summary

With an understanding of ultrasound principles, thorough examination techniques, and knowledge of ultrasound characteristics of a variety of intraocular pathologies, B-scan ultrasound of the eye is a vital part of an ophthalmologist's diagnostic armamentarium. Without this tool, the clinician may not be able to detect or manage a variety of ocular diseases. However, as with any technical skill, B-scan ultrasound requires training, time, and experience to achieve a high level of both confidence and quality imaging.

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Contributor Information and Disclosures
Author

Rhonda G Waldron, MMSc, COMT, CRA, ROUB, CDOS Senior Associate in Ophthalmology, Diagnostic Echographer, Department of Ophthalmology, Emory University School of Medicine

Rhonda G Waldron, MMSc, COMT, CRA, ROUB, CDOS is a member of the following medical societies: Association of Technical Personnel in Ophthalmology, Ophthalmic Photographers' Society, Societas Internationalis Pro Diagnostica Ultrasonica in Ophthalmologia

Disclosure: Received educational grants from Accutome, Alcon, AMO, Carl Zeiss Meditec, Ellex Inc., Haag-Streit, Quantel Medical, and Sonomed for speaking and teaching. .

Coauthor(s)

Thomas M Aaberg, Jr, MD Clinical Assistant Professor, Department of Surgery, Michigan State University College of Human Medicine; Consulting Staff, Department of Ophthalmology, Retina Specialists of Michigan

Thomas M Aaberg, Jr, MD is a member of the following medical societies: Alpha Omega Alpha, American Society of Retina Specialists, Retina Society, Michigan Society of Eye Physicians & Surgeons, American Academy of Ophthalmology, American Medical Association

Disclosure: Serve(d) as a director, officer, partner, employee, advisor, consultant or trustee for: synergetics, True Vision, B&L<br/>Serve(d) as a speaker or a member of a speakers bureau for: Allergan.

Specialty Editor Board

Mary L Windle, PharmD Adjunct Associate Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Nothing to disclose.

J James Rowsey, MD Former Director of Corneal Services, St Luke's Cataract and Laser Institute

J James Rowsey, MD is a member of the following medical societies: American Academy of Ophthalmology, American Association for the Advancement of Science, American Medical Association, Association for Research in Vision and Ophthalmology, Florida Medical Association, Sigma Xi, Southern Medical Association, Pan-American Association of Ophthalmology

Disclosure: Nothing to disclose.

Chief Editor

Timothy Jang, MD Associate Professor of Clinical Medicine, University of California, Los Angeles, David Geffen School of Medicine; Director of Emergency Ultrasonography, Department of Emergency Medicine, Harbor-UCLA Medical Center

Timothy Jang, MD is a member of the following medical societies: American College of Emergency Physicians, American Institute of Ultrasound in Medicine, Christian Medical and Dental Associations, Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Additional Contributors

Richard W Allinson, MD Associate Professor, Department of Ophthalmology, Texas A&M University Health Science Center; Senior Staff Ophthalmologist, Scott and White Clinic

Richard W Allinson, MD is a member of the following medical societies: American Academy of Ophthalmology, American Medical Association, Texas Medical Association

Disclosure: Nothing to disclose.

References
  1. Kendall CJ, Prager TC, Cheng H, Gombos D, Tang RA, Schiffman JS. Diagnostic Ophthalmic Ultrasound for Radiologists. Neuroimaging Clin N Am. 2015 Aug. 25 (3):327-65. [Medline].

  2. Qureshi MA, Laghari K. Role of B-scan ultrasonography in pre-operative cataract patients. Int J Health Sci (Qassim). 2010 Jan. 4(1):31-7. [Medline]. [Full Text].

  3. Byrne SF, Green RL. Ultrasound of the Eye and Orbit. 2nd ed. St. Louis, Mo: Mosby Year Book; 2002.

  4. Mustafa M, Montgomery J, Atta H. A novel educational tool for teaching ocular ultrasound. Clin Ophthalmol. 2011. 5:857-60. [Medline]. [Full Text].

  5. Vodapalli H, Murthy SI, Jalali S, Ali MJ, Rani PK. Comparison of immersion ultrasonography, ultrasound biomicroscopy and anterior segment optical coherence tomography in the evaluation of traumatic phacoceles. Indian J Ophthalmol. 2012 Jan-Feb. 60(1):63-5. [Medline]. [Full Text].

  6. Parchand S, Singh R, Bhalekar S. Reliability of ocular ultrasonography findings for pre-surgical evaluation in various vitreo-retinal disorders. Semin Ophthalmol. 2014 Jul. 29 (4):236-41. [Medline].

  7. Agarwal A, Fan S, Invernizzi A, Do DV, Nguyen QD, Harms NV, et al. Characterization of retinal structure and diagnosis of peripheral acquired retinoschisis using high-resolution ultrasound B-scan. Graefes Arch Clin Exp Ophthalmol. 2016 Jan. 254 (1):69-75. [Medline].

  8. Singh R, Invernizzi A, Agarwal A, Kumari N, Gupta A. Enhanced depth imaging spectral domain optical coherence tomography versus ultrasonography B-Scan for measuring retinochoroidal thickness in normal eyes. Retina. 2015 Feb. 35 (2):250-6. [Medline].

  9. Coleman DJ, Silverman RH, Lizzi FL, Rondeau MJ. Ultrasonography of the Eye and Orbit. 2nd ed. Lippincott Williams & Wilkins; 2006.

  10. Byrne SF, Green RL. Ultrasound of the Eye and Orbit. St. Louis, Mo: Mosby Year Book; 1992.

  11. DiBernardo C, Schachat AP, Fekrat S. Ophthalmic Ultrasound: A Diagnostic Atlas. New York: Thiemes Medical Publishers, Inc; 1998.

  12. Harrie RP. Clinical Ophthalmic Echography: A Case Study Approach. New York, NY: Springer Science+Business Media, LLC; 2008.

  13. Kendall CJ. Ophthalmic Echography. Thorofare, NJ: Slack Incorporated; 1990.

 
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A-scan image of an eye with a traumatic vitreous hemorrhage, posterior vitreous detachment layered with blood, and peripheral choroidal detachment. A thin, parallel sound beam passes through the eye, imaging one small point through the tissues as it passes. The echoes returned to the probe in A-scan mode (left) are converted to spikes that arise from baseline, the amplitude of which is determined by the strength of the echo, giving the examiner information regarding the density of the tissues.
B-scan image of the same traumatic vitreous hemorrhage, posterior vitreous detachment, and low-lying choroidal detachment. An oscillating sound beam passes through the eye, displaying a slice of tissue in one image. The echoes returned to the probe are displayed as a series of dots that form an image, the brightness of which is determined by the strength of the echo, allowing the examiner to determine the density of the tissue for diagnostic purposes.
Shadowing caused from sound absorption by the calcium within a choroidal osteoma. Calcium is so dense that no sound can penetrate it to travel on to the next structure.
Transverse scan of a choroidal melanoma. This is a lateral slice through the lesion centered at the 5:00 position left eye, with 3 clock hours represented both above (2:00, 3:00, and 4:00 positions, respectively, from the top) and below (6:00, 7:00, and 8:00 positions) the lesion.
Longitudinal scan of the same choroidal melanoma. This is a radial slice through the lesion, with 1 clock hour (in this case, the 5:00 position) being represented from the optic nerve and posterior pole (at the bottom of the right side) outward to the anterior meridian.
Axial scan of the same melanoma. The posterior lens surface is seen centrally to the left of the scan, and the optic nerve shadow is seen centrally on the right. Because the lesion is situated below midline, the marker is directed opposite the lesion, or at the 11:00 position, with the 5:00 position lesion displayed inferior to the nerve, and the 11:00 position displayed above the nerve.
Horizontal macula scan in an eye with a vitreous hemorrhage. The posterior lens surface is seen centered to the left, with the macula centered to the right. The optic nerve is seen just above the macula, since the marker is directed nasally.
Vertical macula scan of an eye with a mild vitreous hemorrhage and a submacular hemorrhage. The posterior lens surface is centered to the left, with the macula centered to the right. Because the slice is vertical through the visual axis, the optic nerve shadow is not displayed.
Transverse macula scan of an eye with macular edema. This is also a vertical scan through the macula, so the optic nerve is not seen. Because the probe is held on the sclera rather than the cornea, the crystalline lens is bypassed and not imaged to the left.
Longitudinal macula scan in an eye with macular edema. The optic nerve shadow is seen at the bottom of the right side of the scan, with the macula just above. The probe is held on the sclera rather than the cornea, therefore bypassing the crystalline lens. The lateral rectus muscle is seen in the orbit.
Immersion B-scan image of an iris melanoma extending into the ciliary body. To the left side of the scan is the scleral shell filled with methylcellulose, with the cornea and iris seen centrally and the posterior segment seen on the right.
High-resolution B-scan images of an iris melanoma. This imaging requires a separate probe, and it delivers high magnification and superior detail of the small structures of the anterior segment. On the left is a longitudinal, or radial, scan, and on the right is a transverse, or lateral, scan.
Low reflective vitreous opacities and a posterior vitreous detachment as seen with normal aging of the eye.
Asteroid hyalosis. The calcium soaps in this condition cause the dots within the vitreous cavity to be much brighter than those seen with vitreous hemorrhages.
Vitreous hemorrhage with a retinal tear at the 1:30 position. Note the vitreous hyaloid attaching to the tip of the tear. This is a longitudinal scan, which is necessary to display the tear due to the radial direction of the flap.
Total retinal detachment and vitreous hemorrhage. The retinal detachment appears as a somewhat wavy membrane of high reflectivity in an open-funnel configuration, attaching at the optic disc and out peripherally at the ora serrata.
Retinoblastoma. Note the small, highly reflective echodensities within the tumor, which are foci of calcium.
Persistent hyperplastic primary vitreous. Note the thin membrane of low reflectivity emanating from the optic disc to the posterior lens surface. A longitudinal scan is needed to image the membrane in its entirety, as opposed to a cross section transverse scan, which would demonstrate only a small, weak dot in the central vitreous cavity. Highest gain is also necessary because the membrane is a very weak signal.
"Kissing" hemorrhagic choroidal detachments. The thick, bullous membranes meet in the central vitreous cavity. The underlying opacity is indicative of underlying hemorrhage.
Collar-button shaped choroidal melanoma. The lesion began as a dome shape, then broke through the Bruch membrane to form the button on the anterior surface of the dome. Note the diagnostic A-scan pattern typical of melanoma, with the high retinal spike on the surface of the lesion but low-to-medium internal reflectivity within the lesion. The sclera and orbital tissues are seen as spikes to the right of the lesion.
Metastatic choroidal lesion from the breast. The lesion has rather irregular borders, with medium-high, irregular internal reflectivity on both B-scan and diagnostic A-scan.
Choroidal hemangioma with an associated exudative retinal detachment. This lesion is composed of tightly compacted blood vessels and, therefore, demonstrates high, regular internal reflectivity on both B-scan and diagnostic A-scan.
Ciliary body detachment as seen on high-resolution scan. Note the large cleft in the subciliary space.
Nodular posterior scleritis with fluid in the Tenon capsule. The scan on the right demonstrates a positive T-sign at the insertion of the optic nerve.
Posterior staphylomas. The uvea in this patient has become so thin that it is bulging posteriorly in the macular area and just nasal to the disc.
Optic nerve cup. Note the indentation to the optic disc, a result of increased intraocular pressure in glaucomatous diseases.
Optic nerve head drusen. Note the highly reflective echodensity of the calcium.
Increased subarachnoid fluid around the optic nerve. Note the positive crescent sign.
 
 
 
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