Ординатура / Офтальмология / Английские материалы / Ultrasonography of the Eye and Orbit 2nd edition_Coleman, Silverman, Lizzi_2006

Angle Recession

High frequency ultrasound is able to depict anterior chamber geometry and can demonstrate an abnormal deepening of the anterior chamber and widening of the angle as seen in recession. These findings, as seen in Figure 3.140, indicate the severity of the trauma to the anterior segment.

Dislocated Lens

In any form of severe concussion, the lens may become subluxated or totally dislocated from its usual lens position. Even minor variations in position may be portrayed with the B-scan ultrasound display. Figure 3.141 shows an anterior displacement of the intraocular lens, and Figure 3.142 shows dislocation of the intraocular

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lens still in the capsular bag. In contusion injuries, the crystalline lens is usually not ruptured and maintains its normal configuration, but presence of capsular rupture or cataract (Figure 3.143) can be seen and can indicate the need for lensectomy/vitrectomy.

Figure 3.140. 50-MHz B-scan following trauma showing recession of the angle.

Lens Injuries

The interior of the lens is normally anechoic. Intralenticular echoes can therefore indicate early cataract formation secondary to perforation. Identification of a rupture of the posterior lens capsule with dispersion of lens material into the anterior vitreous can indicate the need for early lens extraction with anterior vitrectomy, as noted earlier.

Vitreous Hemorrhage

Vitreous hemorrhage occurs frequently following ocular trauma and has already been discussed extensively. To reiterate, light diffuse vitreous hemorrhage is usually anechoic, although coagulation and clotting accompanying more massive hemorrhage will appear as reflective aggregates within the posterior chamber. As mentioned, the density, location, and extent of hemorrhage can be well demarcated with the B-scan display. In younger patients with formed vitreous, this demarcation may orient the examiner to sites of stress and thus possible retinal tears.

Figure 3.141. Intraocular lenses are the most common form of foreign body examined at high frequency. This 50-MHz B-scan shows a lens displaced anteriorly, with the trail of echoes indicating the position of a folded haptic.

Figure 3.142. An intraocular lens is outlined with its position dislocated temporally but still in the capsular bag. (See also Figure 3.157 and DVD.)

Penetrating injuries into the vitreous nearly always produce vitreous changes visible acoustically. In young individuals, who suffer the majority of traumatized eyes, the solid vitreous permits a track of hemorrhage to be traced through the entire vitreous compartment. If this path leads to the posterior globe wall, perforation must be expected. Surgery can then be directed to the correct quadrant, minimizing unnecessary exploration and reducing the possibility of extrusion of ocular contents through an unidentified posterior laceration. A posterior perforation

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site can be localized with reference to its distance from the limbus as well as the correct meridian, so that during surgical exploration the wound can be examined (often with vitrectomy rather than extended exploration) and appropriate therapy, such as endolase, silicone oil, cryopexy, and scleral buckling, can be instituted.

Figure 3.143. Example of a traumatized globe with shallow chamber and cataractous changes in the crystalline

lens.

Retinal Detachment

We have previously dealt with the ultrasonographic appearance of retinal detachment. To summarize, the vitreoretinal interface produces a high-amplitude echo from the retinal surface, usually allowing identification of this surface in retinal detachment, distinguishing it from hemorrhage along the posterior vitreous membrane caused by trauma. On rapid motion of the eye in kinetic scanning, a recent retinal detachment will usually move freely but maintain its points of attachment at the ora and the disc. In most situations, lower-amplitude echoes characterize a vitreous veil versus a retinal detachment, but this feature becomes less reliable in long-standing vitreal membranes, where the echo heights may approximate those from the vitreoretinal interface, and absolute differentiation may no longer be possible.

Choroidal Rupture, Scleral Injury

Ultrasound can only rarely detect a scleral rupture, but by demonstrating the presence of a hemorrhage in the vitreous and the areas of contiguity between hemorrhage and sclera, choroidal rupture or scleral injury may be deduced (Figure 3.144) (157,158). If rupture at the equator is suspected, the globe should be fully rotated to permit perpendicular examination of this region.

Perforating or Lacerating Wounds

Anterior Segment

As in blunt trauma, hyphema or complete absence of anterior chamber often follows a perforating injury and can be delineated acoustically.

Figure 3.144. 10-MHz B-scan shows a ruptured globe with a break in sclera posterior to an area of subretinal hemorrhage. Often it is the irregular outline of the globe that may be the only clue to a posterior rupture. The actual scleral separation is only rarely, if ever, seen.

Scleral Rupture or Penetration

As noted previously, the presence of scleral rupture may not be ultrasonically noted, but distortion of the globe contour, as seen in Figure 3.145, or a path of blood through the vitreous, can be used to identify the site of perforation.

Choroidal hemorrhage and anterior dislocation of the vitreous, secondary to surgical intervention, may also necessitate ultrasonic evaluation.

Figure 3.145. 10-MHz B-scan of ruptured globe shows distortion of the globe, detached retina, and hemorrhage

debris.

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Foreign Bodies

A major use of ultrasound in ophthalmology has been the localization of intraocular foreign bodies and the determination of their physical properties. Bronson (159) published extensively on the use of ultrasound for the localization of intraocular foreign bodies and described an intraocular forceps directed by ultrasound. The use of ultrasound to identify and localize foreign bodies permits early and directed surgery on patients with an intraocular foreign body, with improved visual results (160).

Radiopaque Foreign Bodies

As noted previously, in evaluating radiopaque foreign bodies, an available CT or x-ray report is useful to the ultrasonographer prior to performing the scan. The number and position of foreign bodies as determined by radiography can be of inestimable help in directing and shortening the ultrasonic evaluation.

Because of the random size and material of foreign bodies, absolute criteria for their identification cannot be supplied. Their distance from the transducer, orientation, and acoustic impedance variation from surrounding tissue all affect the reflected echoes. A rigorous, meticulous search for foreign bodies is thus indicated in all cases where they are suspected. Careful B-scan serial sectioning of the globe and increased attention to the A-scan echo amplitudes are essential. The localization of a foreign body and determination of its magnetic properties may therefore be more time-consuming than routine ocular diagnosis.

Several acoustic features of metallic foreign bodies are demonstrated by Figure 3.146. In this series of ultrasonograms, a metallic foreign body is seen on the retinal surface at the posterior pole. By performing serial scans of the foreign body at a series of decreasing gain settings, the foreign body can be more readily distinguished from surrounding hemorrhage or other tissues. This technique of repeating the serial sectioning at varying sensitivity settings is useful in foreign body localization because it permits distinction of the high-amplitude echoes produced by the foreign body from lower-amplitude echoes produced by the surrounding hemorrhage. This particular ultrasonogram demonstrates three other important acoustic characteristics of metallic foreign bodies:

1.The foreign body tends to reflect sound energy, so that the region posterior to it will appear shadowed, or anechoic. In this scan, the retrobulbar fat has a wedge-shaped shadow resembling an optic nerve shadow in the region directly posterior to the foreign body. This shadow effect is a useful “pointer” to a foreign body.

2.Sound travels faster through metal than through surrounding vitreous. Consequently, the region posterior to the foreign body shows a slight protrusion or prominence of the retina, an artifactual result of the increased transmission velocity of sound through metal. This mound posterior to a foreign body on the retina can be aligned with a shadowed area posteriorly to direct attention to a foreign body (Figure 3.147).

3.Reduplication echoes can act as another “pointer” to the foreign body and are a characteristic of BBs and gas bubbles.

Figure 3.146. Top: B-scan ultrasonogram demonstrating a metallic fragment at the back of the eye surrounded by hemorrhage. Middle: Reduced gain (a lower sensitivity setting) shows the metallic fragment to lie anterior to the retina. Acoustic absorption from the fragment produces shadowing in the orbit, a feature useful in localizing the foreign body. Bottom: Lower sensitivity on both the B- and A-scans demonstrates the higher reflectivity of the foreign body relative to the surrounding tissue.

Figure 3.150. Left: 10-MHz B-scan image shows glass foreign body temporally. Note trailing reverberation artifact. Right: 50-MHz image shows foreign body to be resting on lens at the level of zonular insertion.

Figure 3.151. Small wood fragment seen in the iris at 50 MHz. These fragments are almost impossible to see at

lower frequencies.

Figure 3.152. An IOL haptic displaced posteriorly into the ciliary processes, causing symptoms that required

repositioning of the lens.

TABLE 3.6 Uses of Ultrasound in Intraocular Foreign Body Management

Foreign Body Localization

Axial Length Measurements to Augment X-ray Localization

Assessment of Associated Globe Damage

Determination of Magnetic Properties Using Pulsed Magnet

Extraction of Nonmagnetic Foreign Bodies Using Ultrasonic Data

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20-Megahertz Imaging

Conventional ultrasound examination of the eye and orbit is performed at a frequency of approximately 10 MHz. Very high frequency ultrasound, or ultrasound biomicroscopy, involves frequencies of 25 MHz or higher, and, because of the effect of attenuation, VHF ultrasound is restricted to the anterior segment. There is, however, a midrange of frequencies that has recently been introduced to clinical practice. At 20 MHz, spatial resolution is double that attainable at 10 MHz and attenuation, although significant, remains small enough to permit imaging of both the posterior and anterior segments. We use an immersion 20-MHz imaging system for evaluation of the posterior segment. Examples of images produced using this system are provided in Figure 3.153. Commercial ultrasound systems using 20-MHz transducers have been developed for imaging of both the anterior and posterior segments. Innovative Imaging, Inc., produces a system designed for wide-angle imaging of the anterior segment. In this sector scan system, the transducer may be coupled to the eye either with a fluid standoff established with a scleral shell or by enclosing the tip of the transducer in a fluid-filled sheath (tono-tip), which is then placed in contact with the globe. Quantel Medical produces a 20-MHz enclosed sector scan probe (Figure 3.154) as an option with their 10-MHz B-scanner, and a similar system is produced by Optikon. Although 20-MHz images of the anterior segment do not provide the resolution of VHF systems, they can, in many instances, provide clinically significant information in situations where 10-MHz systems are inadequate, allowing, for instance, assessment of IOL placement, glaucoma syndromes, hypotony, tumors, and cysts. Imaging of the posterior segment at a frequency of 20 MHz allows improved assessment of pathologies, such as macular degeneration, cystoid macular edema (Figure 3.155), retinal holes, and small tumors.