Chapter 19. Ocular

Ultrasound of the globe and orbit can be very helpful in evaluating ED and critical care patients with serious eye complaints or potentially elevated intracranial pressure. In many acute ocular conditions, the physical examination is difficult and may be unreliable. Specialized equipment and ophthalmologic expertise are frequently unavailable in the ED, especially on nights, evenings, weekends, and holidays. In these circumstances, ultrasound is more accurate than traditional examination techniques for assessing a wide variety of ocular and orbital diseases, including penetrating globe injuries, retinal detachment, and papilledema.1–4

The eye is an ideal structure for ultrasound interrogation since the anterior chamber and vitreous cavity are fluid filled. With ultrasound, the globe, orbit, and retrobulbar structures can be evaluated accurately and safely.2 While ophthalmologists typically use highly specialized ultrasound transducers, ocular ultrasound is performed using transducers readily available to emergency providers.5–8 This technology can accurately differentiate between pathology requiring immediate ophthalmologic consultation and that which can be followed up on an outpatient basis.

Physical examination incorporating ophthalmoscopic and slit lamp examination is the primary diagnostic approach to most ocular complaints. There are many situations in which the physical examination may be limited and imaging is required. Ultrasound examination of the eye is potentially useful in many situations encountered in emergency and acute care settings. Since physical examination requires a clear visual axis to examine the structures of the eye, any obstruction, such as blood in the anterior chamber or vitreous, obscures visualization and limits physical examination. Ultrasound allows imaging beyond the obstruction. There is little attenuation of the ultrasound signal. Detailed, high-resolution images of posterior structures can be obtained even when direct visualization is difficult or impossible.

Situations in which direct visualization of intraocular structures may be difficult or impossible include lid abnormalities due to facial trauma, severe edema, subcutaneous air, or previous surgeries. In cases of facial trauma and swelling, it may be difficult to assess the eye without significant manipulation, which may be painful and even harmful if there is globe perforation. Visual axis obstruction can also occur in the presence of corneal scars, cataracts, hyphema, or hypopyon, or with vitreous hemorrhage. Furthermore, normal conditions such as miosis make visualization of the retina difficult without pharmacologic agents.

Ultrasound may also be helpful in situations where physical examination alone is inadequate. An example is peripheral retinal detachment. Patients presenting with a history consistent with retinal detachment may have an unremarkable ophthalmologic examination, and performing an examination with a dilated pupil is not always feasible. Ultrasound allows for visualization of the entire retina without dilation of the pupil.

CT is frequently employed to evaluate the globe after trauma. CT is highly sensitive for orbital fractures, foreign bodies, and retrobulbar hematomas. Fine-cut CT scans with 2-mm sections are able to localize foreign bodies as small as 0.7 mm.9 In contrast, ultrasound has been demonstrated to have a slightly lower sensitivity but a comparable positive predictive value for detecting similar size metal foreign bodies in a porcine model.10 Patients with a potential foreign body and a negative ultrasound examination will require an orbital CT scan.

The clinical indications for ocular ultrasound are as follows:

• Eye trauma
• Acute change in vision
• Headache, head trauma, or altered mental status (potentially elevated intracranial pressure)

Eye Trauma

Trauma is one of the leading causes of unilateral loss of vision in the United States and accounts for an estimated cost of $200 million per year.11 Vision-threatening injuries include retrobulbar hematoma, retinal detachment, lens dislocation, traumatic optic neuropathy, and globe injuries.12 The most common presentation for a vision-threatening injury is blindness after the injury. However, vision loss may occur gradually because of unrecognized trauma or the patient may not be able to report vision loss due to lid swelling or alteration in mental status. As a consequence, ocular injuries are often missed in these patients. A retrospective review of trauma patients with potential ocular injury demonstrated that nonophthalmologists frequently missed or underestimated potential eye trauma, diagnosing only 72% of eye injuries and referring only 27% for ophthalmologic evaluation.13

Significant swelling of the periorbital tissues can be encountered with midface or craniofacial fractures, injuries that increase the risk of concomitant ocular injury. One study found that of 283 patients presenting with facial fractures, 71 had an ocular injury, with 32 (12%) suffering a serious ocular injury.14 While it is ideal for all facial trauma patients with suspected eye injury to have an examination performed immediately by an ophthalmologist, this is commonly not feasible. There are often more serious and life-threatening injuries that require emergent evaluation and treatment.

Ocular ultrasound can be performed at the bedside. It is noninvasive, so there is little risk for exacerbating an injury when it is performed correctly. Ocular ultrasound is useful even when medication, drugs, or hypoxia alter pupillary function. This is important in the initial clinical assessment of the eye, where pupil size, reaction to light, and the presence or absence of a relative afferent papillary defect are assessed.12

Retrobulbar hemorrhage can be diagnosed clinically when a significant hematoma is present.15 However, this vision-threatening emergency often goes unrecognized, especially in trauma victims with a decreased level of consciousness, and delayed diagnosis may result in irreversible damage to the optic nerve. CT typically reveals stretching of the optic nerve and a tented posterior sclera. Retrobulbar hematoma may cause damage to the optic nerve either through direct compression leading to ischemia or through traction by propelling the globe forward and stretching the nerve. The hematoma occurs as a result of bleeding within or around the cone formed by the extraocular muscles. This cone of muscles combined with the bony orbit forms a compartment in which ongoing hemorrhage leads to elevated intraorbital pressure. As the pressure rises, compression of the ophthalmic and retinal vessels can occur, resulting in ischemia and ultimately blindness.12 Any potential injury must be treated rapidly because irreversible damage may occur after only 60 minutes of ischemia.16

An open globe injury is defined as a full thickness wound involving the corneoscleral wall of the eye. This type of injury is typically caused either by blunt force, particularly to the anterolateral part of the orbit, or due to laceration by a foreign body.12,17 While some open globe injuries are obvious with vitreous extrusion, a significant proportion are not readily apparent. Clues to an open globe injury include bloodstained tears, lid lacerations, presence of a significant subconjunctival hemorrhage, or hyphema. However, none of these are pathognomonic for globe rupture. Furthermore, in cases involving small high-velocity projectiles, there may be no external signs of perforation.12 Standard CT evaluation for open globe injury has been shown to have a sensitivity and specificity of 75% and 93%, respectively.18 Ultrasound sensitivity is similar to a standard CT scan. The best test for identifying globe injury is thin slice CT (2-mm) with reconstructions, which can identify subtle findings such as scleral discontinuity.

Thin slice CT is also the test of choice for intraocular foreign body localization.9 Ultrasound has limitations when used for the detection of intraocular foreign bodies. In animal models, the sensitivity and specificity were 87.5% and 95.8%, respectively.10 One study compared CT with ultrasound in a prospective study of patients with opaque intraocular foreign bodies. Ultrasound had complete concurrence with surgical or clinical follow-up in 90% of 61 cases. The study concluded that ultrasound was useful, even though CT was more accurate in detecting the intraocular foreign bodies, because ultrasound was superior to CT in demonstrating intraocular damage associated with the foreign bodies.

Acute Change in Vision

Acute change in vision is a fairly common complaint in emergency and acute care settings. Symptoms may include floaters, flashing lights, double vision, and even complete blindness. Although these symptoms may be indicative of nonocular problems, they require rapid attention to exclude such processes as lens dislocation, vitreous hemorrhage, retinal detachment, and vitreous detachment.

Lens dislocation is a condition frequently caused by blunt trauma. In a series of 71 consecutive patients presenting with ocular trauma, 12 were noted to have a lens dislocation.19 Lens dislocation can also occur without trauma and be idiopathic or hereditary (Marfan's syndrome). Ultrasound easily identifies the lens due to its anterior location. Using ultrasound, the clinician is able to evaluate the lens-supporting structures to determine whether the lens is subluxed or completely dislocated. Subtle lens subluxation can be a difficult diagnosis, even for experienced clinicians.

The incidence of spontaneous vitreous hemorrhage is about 7 cases per 100,000 people.20 Proliferative diabetic retinopathy, posterior vitreous detachment with or without a retinal tear, and retinal detachment are the most common causes. Symptoms of a spontaneous vitreous hemorrhage typically include floaters or clouded vision. Other symptoms such as flashes of light may be present, but these symptoms are usually due to the underlying cause of the hemorrhage, such as retinal detachment. As a vitreous hemorrhage ages, a membrane may form with attachments to the retina. When this membrane contracts, a retinal detachment may occur, usually weeks after the initial hemorrhage. Ultrasound allows for visualization of the hemorrhage as well as the potential cause. In fact, there is no other imaging modality that can reliably ascertain the anatomic position of the retina.20

Retinal detachments and retinal tears (Figure 19-1), which may be a precursor to detachment, are common causes of vitreous hemorrhage. Both represent a separation between the retinal sensory and the pigment layers. There are three types of retinal detachment: rhegmatogenous, tractional, and exudative. Most cases of rhegmatogenous retinal detachment are associated with a posterior vitreous separation; the detachment is caused by fluid seeping into a break in the sensory layer of the retina. Tractional retinal detachments occur when fibrous membranes in the vitreous pull the retina from the underlying retinal pigment epithelium, and they are typically seen with proliferative diabetic retinopathy or as a common sequela of aging. However, this condition is also associated with retinopathy of prematurity, sickle cell retinopathy, and prior vitreous hemorrhage. Exudative retinal detachment occurs with inflammatory, infectious, or neoplastic conditions that disturb the blood–retina barrier. This allows fluid to collect underneath the layers of the retina causing a separation. In most cases of retinal detachment, patients will complain of flashing lights, floaters, or a curtain-like vision loss.21 As the retinal tear progresses, retinal vessels may tear, producing a vitreous hemorrhage. This is a common association and is why patients with retinal detachments typically complain of floaters prior to the onset of peripheral or total vision loss.

Posterior vitreous detachment is a separation of the vitreous humor from the retina (Figure 19-1). The separation is painless and usually abrupt; patients complain of new floaters in conjunction with the onset of flashing lights. The clinical history can be similar to retinal detachment as patients with both problems complain of flashing lights at onset. This entity is a common presentation for acute visual change in the urgent care and emergency settings as it is a normal consequence of aging. The condition occurs often in older adults and over 75% of those greater than age 65 develop it.22 Vitreous detachment often has a benign clinical course that does not significantly threaten visual acuity; however, in approximately 15–30% of cases of vitreous detachment, a retinal hole is created that may lead to retinal detachment. Posterior vitreous detachment can also be associated with vitreous hemorrhage.23 Ultrasound is the modality of choice for evaluating the retina and vitreous. Ultrasound may be the only method for detecting posterior vitreous detachment and is also more accurate for identifying potential associated complications (retinal detachment or hemorrhage).

Headache, Head Trauma, or Altered Mental Status

Headache, head injury, and altered mental status are common presentations in the ED. These complaints may be associated with elevated intracranial pressure. While many modalities are available to evaluate potential elevated intracranial pressure, each has significant limitations. In the acute trauma patient, evaluating the presence of papilledema with an ophthalmoscope is difficult. Furthermore, papilledema can take hours to develop. CT is the most common initial diagnostic modality, but it may be unavailable or obtained early in the patients course before elevated intracranial pressure develops. When unstable patients are taken directly to the operating room for abdominal injuries, there may not be time for a head CT. In these patients, ocular ultrasound can provide a method for grossly assessing the intracranial pressure. In addition, multiple examinations can be readily performed on the same patient with an evolving clinical picture.

A direct communication between the subarachnoid space of the ventricles and the optic nerve sheath has been described in cadavers and an animal model. In an experimental model using rhesus monkeys, change in the optic nerve sheath diameter in response to changing intracranial pressure was demonstrated by varying the pressure in balloons placed in the subarachnoid space.24 Multiple clinical studies have demonstrated this effect in actual patients. One study comparing CT to ultrasound measurement of the optic nerve sheath diameter in patients with suspected intracranial hemorrhage showed a sensitivity and specificity of 100% and 95%, respectively.25 This procedure has also been described in pediatric patients.26

The globe is an oblong structure with a mean vertical diameter of 23.5 mm and mean anteroposterior diameter of 24 mm. The eye is embedded in the orbit and covered by the eyelids. On ultrasound evaluation, the surrounding facial bones appear as bright reflectors with deep posterior shadowing. The lid is echogenic and divided by the hypoechoic tarsal plate.

The eye is divided into anterior and posterior segments. The anterior segment consists of the cornea, anterior chamber, iris, posterior chamber and lens. The posterior segment consists of the structures posterior to the lens; the vitreous chamber, retina, choroid, and optic nerve. The cornea appears as a thin, hyperechoic structure attached to the sclera at the periphery. The sclera is a dense membrane to which the extraocular muscles attach, but is indistinguishable from the lateral structures of the eye by ultrasound. Anechoic aqueous humor fills the anterior chamber, and echoes in the anterior chamber are seen only in pathologic states. The iris and pupil can often be visualized between the anterior chamber and the lens. The lens appears as a hyperechoic reflector, which is concave, and may show reverberation artifact at the anterior surface (Figure 19-2).

The posterior segment comprises the majority of the globe, about 80%. It contains the vitreous body, which consists of a colorless, structureless transparent gel, approximately 99% of which is water. The normal vitreous body is echolucent (dark on ultrasound); however, ultrasound artifacts may occasionally be seen.

The posterior layers of the eye consist of the retina and choroid, which are bounded by the sclera. The retina is the neural, sensory stratum of the globe. It is very thin, varying from 0.56 mm near the optic disk to 0.1 mm anteriorly. Its anterior surface is in contact with the vitreous body and the posterior surface is strongly adherent to the choroid. Near the center of the posterior aspect of the retina is the oval macula, where visual resolution is the greatest. At the macula, the retina is only a few cell layers thick. The choroid is a thin, highly vascular membrane lining the posterior globe. It is firmly adherent to the sclera and is thicker posteriorly where it is penetrated by the optic nerve. Its internal surface is firmly attached to the pigmented layer of the retina. On ultrasound interrogation of the normal eye, the three posterior layers (retina, choroid, and sclera) blend into one homogeneous structure. If separation occurs as with retinal detachment, the layers may be distinguished from one another.

The optic nerve and sheath may be seen posterior to the globe, traveling toward the optic chiasm. The nerve appears homogeneous on ultrasound, with low internal reflectivity (Figure 19-3). This is in contrast to the more reflective sheath.27 Measurement of the sheath is made 3 mm posterior to the globe (Figure 19-4). Normal measurements vary by age from 5 mm and less in adults, 4.5 mm in children (1–15 years), and 4 mm or less in children less than 1 year of age.25–27 Since the optic nerve sheath is connected to the subarachnoid space and is easily distensible, conditions that elevate the intracranial pressure lead to dilation of the optic nerve sheath.

Arterial and venous structures of the eye can be identified using color Doppler. The largest artery in the orbit is the ophthalmic artery, which runs parallel to the optic nerve.28 The central retinal artery is located in the anterior part of the optic nerve shadow. The central retinal vein is found near the central retinal artery and is distinguishable from the central retinal artery with pulsed wave Doppler (PWD) examination.29

Patient positioning will vary, with trauma patients typically supine while other patients may be partially reclined or upright. Patients with a potential penetrating injury may be reclined at 45°. Make the patient comfortable with oral or parenteral medications. When a ruptured globe is suspected, consider administering antiemetics to prevent retching and a resultant rise in intraocular pressure. Topical anesthetic and cycloplegic medications are not necessary for sonographic examination of the globe.

Set the ultrasound machine with the ocular presets, which will help limit the amount of energy exposure to the ocular tissue. Always practice the ALARA (as low as reasonably achievable) principle to ensure that the total ultrasound energy is maintained below a level at which bioeffects are generated while diagnostic information is preserved. Use a linear array transducer in the 7.5–15 MHz frequency range (the same transducer utilized for line placement, soft tissue examinations, and musculoskeletal studies). Higher transducer frequencies may produce better images, but decreased penetration may limit visualization of retro-orbital structures. Use an endocavity transducer if a linear transducer is not available1; however, manipulating an endocavity transducer over the eye can be awkward and imaging is somewhat limited. Color and spectral Doppler capabilities allow for the evaluation of orbital vasculature and may be helpful in specific cases. An ocular or small parts setting is available on most machines. Other presets such as thyroid, musculoskeletal, and superficial settings may also be used. Sterile gel is typically not required but can be utilized.

The amount of ultrasound gel needed for ocular ultrasound depends on the possible pathology. If globe rupture or pathology in the very near field is suspected, then use a larger amount of gel to fill the preorbital space. With the eyelid closed during the examination (Figure 19-5), allow the transducer to “float” on the ultrasound gel while not touching the eyelid. If the lid is not touched and no pressure is transmitted to the globe, the possibility of vitreous extrusion from a perforated globe is minimal. The space between the transducer and the eyelid can be clearly visualized during the ultrasound examination as an echo-free space between the top of the screen and the lid, and confirms that no pressure was applied to the globe during the examination (Figure 19-6A). If globe rupture is suspected, it is advisable to have the patient keep both eyes closed so they are less likely to inadvertently open the eye being examined. If a ruptured globe is not suspected, then very light contact with the eyelid is permitted, but will still require a moderate amount of gel. The gel is nontoxic to ocular structures; however, removal of gel from the preorbital space may be difficult in a patient with a painful eye condition. Further, some patients complain of a burning sensation if the gel comes in contact with the cornea. When the transducer touches the eyelid, near-field structures are too close to the transducer and are not well visualized, which is in contrast to when the transducer is “floated” within the ultrasound gel (Figure 19-6B).

Gently place the transducer onto the closed eyelid using normal ultrasound conventions for transducer orientation (transducer indicator points to the top of the head for longitudinal views or to the patient's right for transverse views). After placing the transducer into the gel, pay particular attention to the ultrasound image, leaving a stripe of echolucent gel anterior to the eyelid. This gel separation must be maintained if there is a possibility of globe rupture. Simply suspending the transducer over the patient's eye will inevitably lead to a shaky image and compression of the globe as the clinician's arm grows tired. By resting a portion of the hand holding the transducer on a bony structure such as the ridge of the nose or the patient's eyebrow, the clinician can stabilize the transducer and avoid resting the transducer directly on the eyelid. It is common to use pressure to improve ultrasound imaging when performing abdominal ultrasound; however, with ocular ultrasound, pressure on the globe must be avoided (Video 19-1: Ocular Normal).

Adjust the gain on the ultrasound machine several times throughout the examination. If the gain is too high initially, artifacts will be created, making the examination difficult (Figure 19-7). Setting the gain too low will cause a small vitreous hemorrhage or subtle detachment to be missed. Thus, if the examination is started with normal gain settings, at some point the gain should be turned up to evaluate for subtle pathology (Figure 19-8). As the gain is increased, however, artifacts will be visualized that may mimic a vitreous hemorrhage. Comparison with the nonsymptomatic eye can help differentiate true vitreous hemorrhage from artifact associated with high gain. Adjust the focal position to the area of interest. This will change throughout the examination as the clinician examines the structures in the near field and far field.

Ultrasound imaging almost always involves visualizing structures in two orthogonal planes. Since each plane creates only a two-dimensional (2D) image, a three-dimensional (3D) mental image is created by scanning in both planes and sweeping from side to side and top to bottom. Both transverse and longitudinal imaging is necessary for an adequate examination (Figure 19-9). Sweep the transducer from side to side in both planes to demonstrate the full extent of the ocular structures, especially when the retinal periphery is being examined. If the patient is cooperative, instruct the patient to move their eye in all four quadrants to avoid missing any pathology. This allows the entire retina to be examined with less transducer movement. Also, movement of the eye is useful in classifying the type of detachment present. Movement of the detachment in response to rapid eye movements is referred to as “after movements.” Vitreous detachments are very mobile and are often referred to as being “jiggly” in the ophthalmology literature. Retinal detachments move with eye motion, but to a lesser extent than vitreous detachments. Choroidal detachments do not demonstrate any movement with rapid eye movements.17

The optic nerve is seen traveling away from the globe posteriorly. The nerve itself is not seen with any great detail. Use minor changes in transducer angle to visualize the optic nerve sheath as clearly as possible. Measurement of the optic nerve sheath diameter is typically made 3 mm posterior to the optic disc. A measurement greater than 5 mm in adults is considered abnormal. Occasionally, the optic nerve sheath may appear dilated despite normal intracranial pressure. When measurements are in doubt, the 30° test can be used. Measurement of the optic nerve sheath is made in primary gaze and then after the patient shifts gaze 30° from primary. In cases of elevated intracranial pressure, the nerve and sheath are stretched with this maneuver and the fluid is distributed in the extended nerve sheath resulting in a smaller diameter than in primary gaze. If nerve sheath enlargement is secondary to parenchymal infiltration or thickening of the optic nerve, there will be no change in the nerve sheath measurement with a shift in gaze.

Color and spectral Doppler measurements are helpful in the diagnosis of several conditions. Blood flow in the retina and the region just posterior to the eye is readily identified with color or power Doppler. With PWD, graphical representation of the blood flow is depicted. When blood flow is evaluated the optic nerve is first located, then the vessels are identified using color Doppler followed by individual assessment with PWD, as each vessel will have a typical waveform.28 When interrogated with PWD, the ophthalmic artery tracing has a similar pattern to that of the internal carotid artery, containing a dicrotic notch. The central retinal artery waveform is more rounded and flat compared with that of the ophthalmic artery. Since Doppler ultrasound is a higher energy mode, it is recommended that these exams be as brief as possible, although no adverse effects have been reported.

Iris and Anterior Chamber Evaluation

In some patients with facial trauma, assessing ocular and pupillary movements is difficult because of facial swelling. Using ultrasound, the iris is easily evaluated if the patient is able to cooperate with the examination. Ask the patient to look superiorly and place the transducer on the inferior portion of the globe in a transverse position. By sweeping the imaging sector cephalad, a frontal plane of the iris and pupil can be acquired. Measure the pupillary size and assess the function of the iris by shining a light in the uninjured eye (Video 19-2: Ocular Abnormal).

With a high-frequency transducer and the appropriate noncontact technique (see above), anterior chamber pathology can be visualized. A hyphema or hypopyon may display an echogenic area within the aqueous (Figure 19-10). Slit lamp examination is the preferred method for diagnosis, but ultrasound may have a role in patients with severe blepharospasm or swelling.

Extraocular Movements

By visualizing eye movement in the orbit, extraocular muscle function can be assessed. If a muscle is entrapped by a fracture, movement will be limited.

Vitreous Hemorrhage

Vitreous hemorrhage frequently accompanies major trauma to the face but can also be idiopathic or associated with retinal detachment, coagulopathy, diabetes mellitus, or central vein occlusion. The ultrasound appearance of vitreous hemorrhage depends on the age and severity of the hemorrhage. In fresh mild hemorrhages, small areas of mildly echogenic mobile vitreous opacities are seen (Figure 19-11). As the hemorrhage ages, particularly with severe hemorrhages, the blood first organizes (Figure 19-12) and then may form membranes. Sonographically, this appears as a vitreous filled with multiple large echogenic opacities. These opacities may layer due to gravity. Occasionally, with a penetrating foreign body, a membrane will form over the tract. This tract may assist in localizing the foreign body.

Globe Perforation

Globe perforation is typically associated with some type of trauma. Sonographically, the globe may be decreased in size, indicating loss of pressure or vitreous. Buckling of the sclera may be seen posteriorly and vitreous hemorrhage is frequently present (Figure 19-13). Subtle perforations may be missed if little vitreous has been lost. A careful look at the anterior chamber is warranted as it may be collapsed from a small perforation.

Foreign Bodies

Ocular foreign bodies are easily identified with ultrasound in most cases. Even if previously detected with another imaging modality, foreign bodies can be more precisely localized with ultrasound.30 Intraocular foreign bodies typically appear as highly reflective objects that may be located in the vitreous (accompanied by a vitreous hemorrhage), in the retina, or in the posterior orbital fat (Figure 19-14A). If embedded in the posterior orbital fat, the foreign body may be missed because of other highly echogenic structures in that region.17 A strongly reflective foreign body may produce a “twinkling” artifact with color Doppler (Figure 19-14B), which appears as a rapidly changing mixture of red and blue.31 Twinkling occurs with any strong reflector including calcifications.

Dislocation of the Lens

Dislocation of the lens is easily visualized when it is significant. Dislocations may be partial (subluxation) or complete (Figure 19-15). With a subluxation, the lens may initially appear to be normal. However, with eye movement, the lens appears to move independently of the surrounding structures. A complete dislocation is more obvious as the lens will be out of its usual position.

Vitreous Detachment

Vitreous detachment occurs most commonly as a normal consequence of aging, but may also occur from trauma or after intraocular surgery. A vitreous detachment often has a C-shaped, concave upward appearance sonographically. The vitreous membrane appears “jiggly” with eye movements, is thinner than a retinal detachment (may be a subtle difference), and is not attached to the margins of the optic disc. This latter point helps to differentiate this condition from posterior retinal detachment (Figure 19-16). If associated with a retinal detachment or tear, these can also occasionally result in a posterior hemorrhage.17 A fibrinous vitreous membrane is sometimes seen when a vitreous hemorrhage leads to a retinal detachment.17

Retinal Detachment

Retinal detachments are important to recognize early as they may progress to full detachments and loss of vision if untreated. Retinal tears, the precursor to detachments, are difficult to see unless they are substantial. When visualized, retinal tears appear to be short, reflective, linear structures protruding into the vitreous.17 Another clue to a retinal tear is the identification of subretinal fluid. Retinal detachments appear as a highly reflective membrane, which seems to “float” in the vitreous (Figure 19-17, Figure 19-18). In contrast to choroidal detachments, where the membrane does not change with eye movements, fresh or recent retinal detachments are mobile with eye movements.17 As the retinal detachment ages, this flexibility is lost and the membrane becomes stiff and slightly thickened (Figure 19-19) When a retinal detachment becomes complete, a connection to the ora serrata is maintained anteriorly as well as posteriorly to the optic disc, and the membrane will have a V or funnel shape within the vitreous cavity. An incomplete retinal detachment that spans the posterior globe will also demonstrate tethering to the margins of the optic disc. This finding helps differentiate a retinal detachment from a vitreous detachment (Figures 19-1 and 19-16).

Choroidal Detachment

Choroidal detachment is the separation of the choroid from the sclera due to blood accumulation from ruptured vessels. This condition is occasionally seen after trauma to the eye or face. It occurs most frequently after intraocular surgery. Choroidal detachment appears as a smooth, dome-shaped, thick structure (or structures, if multiple hemorrhages occur simultaneously) separated from the posterior aspect of the eye (Figure 19-20). If these domes become large enough to touch in the vitreous, this is referred to a “kiss.” Although the choroid itself does not display motion (after movement) with eye movement, echogenic blood inside the choroidal detachment may move with eye movements.

Retrobulbar Hematoma/Hemorrhage

A retrobulbar hematoma is seen as an echolucency just posterior to the globe. Since the orbit is a closed space, pressure may be exerted on the posterior globe by the hematoma. This pressure can be seen sonographically as a distortion in the posterior aspect of the eye (Figure 19-21). As the blood accumulates, retinal vasculature may become compressed and changes in the spectral Doppler pattern of the retinal vessels may also be seen. While ultrasound imaging can be very useful in suspected cases of retrobulbar hematoma, hemorrhage may be difficult or impossible to visualize because the blood may be isoechoic to the other posterior structures. There is a paucity of research concerning the sensitivity and accuracy of ultrasound for determining the presence of a retrobulbar hematoma in the emergency setting.

Optic Nerve

The optic nerve and its surrounding sheath are located posterior to the globe (Figure 19-3). When assessing for possible elevated intracranial pressure, optic nerve sheath diameter measurements are taken 3 mm posterior to the optic disc (Figure 19-4). Maximum measurements vary with age. As mentioned previously, the upper limit in adults is 5 mm, children is 4.5 mm, and infants is 4 mm.2,27 Increasing optic nerve sheath diameter correlates well with increasing intracranial pressure (Figure 19-22). Measurements typically plateau at approximately 7.5 mm even with extremely high intracranial pressure. In cases where the intracranial pressure has been elevated for some time, one can see an echolucent circle within the optic nerve sheath separating the sheath from the optic nerve. This is referred to as the “crescent sign” (Figure 19-23) and is a corollary to funduscopic papilledema. Cadaveric-based research has shown that dilation of the optic nerve sheath occurs simultaneously with elevation of the intracranial pressure. However, the amount of dilation of the optic nerve sheath is not initially proportional to the change in intracranial pressure.32 It is assumed that variation in the rate of change between the intracranial pressure elevation and the change in optic nerve sheath dilation is due to a redistribution of the cerebrospinal fluid. Furthermore, the development of the crescent sign does not occur immediately with elevated intracranial pressure. The amount of time required to develop the crescent sign is not known. However, this sign is often seen in conditions with chronically elevated intracranial pressure such as pseudotumor cerebri.

Masses

During the emergency ocular ultrasound examination, other nonemergent abnormalities may be encountered. One example is the incidental discovery of a mass. Symptoms of primary ocular cancer or metastatic disease involving the eye include blurry vision, distorted vision, blind spots, white pupils, red eye, eye pain, and vision loss. Many of these symptoms are neither specific nor sensitive for cancer. Furthermore, many ocular tumors produce no symptoms at all. The review and description of ocular tumors are beyond the scope of this chapter. The detection of a potential mass requires ophthalmologic follow-up.

Retinoschisis

Retinoschisis is a separation in the layers of the retina and may occasionally be encountered in the emergency setting. Differentiating retinoschisis from a retinal detachment is difficult. By ultrasound, retinoschisis is more focal, smooth, and dome-shaped than a retinal detachment. In the emergency setting, differentiation between the two processes is not as critical as identifying the abnormality on ultrasound and obtaining ophthalmologic consultation.

Central Retinal Artery and Vein

Central retinal vein or artery occlusion may present as painless visual loss that may or may not be complete. Utilizing color and PWD just behind the globe will allow an evaluation of the blood supply to the eye (Figure 19-24). Color Doppler typically shows two directions of blood flow (usually red toward and blue away from the transducer). Placing a PWD gate over each flow direction will allow observation of venous and arterial flow patterns (Figure 19-25A,B). The absence of either arterial or venous flow on the PWD strongly suggests a vascular cause in the patient with sudden and painless loss of vision. The use of Doppler ultrasound to evaluate these conditions generally requires significant experience, however, since abnormalities are usually unilateral, comparison of flow in the affected and unaffected eyes may allow relatively inexperienced providers to obtain valuable information.28

Age-Related Vitreous Changes

With age, syneresis (shrinkage of the vitreous humour) often leads to posterior vitreous detachment, which is benign unless hemorrhage or a retinal tear occurs. As a result of syneresis, or contraction and degeneration of the vitreous gel, a posterior vitreous separation may occur. Another benign condition occasionally detected by ultrasound is asteroid hyalosis. This appears as multiple pinpoint and highly reflective vitreous opacities due to reflective calcium salts that are accumulated in the vitreous.

Intraocular Pressure Elevation

Elevated intraocular pressure may be noted with PWD. As the intraocular pressure rises, the central retinal artery is compressed. With progressive compression, the peak systolic velocity (PSV) and the end-diastolic velocity (EDV) of the central retinal artery decrease. In addition, the resistive index (RI) of the central retinal artery increases. The RI is the ratio of the difference in the PSV and the EDV divided by the PSV {RI = (PSV−EDV)/PSV}.29 One study that evaluated a healthy eye model showed that these measured differences in flow could accurately predict the presence of elevated intraocular pressure.33

1. Safety issues. From the standpoint of worsening an underlying injury, an ultrasound examination of the eye is safe if the techniques described in this chapter are followed. In patients with a potential globe perforation, ocular ultrasound may be safely performed by using a large amount of gel and “floating” the transducer on the gel, so that the transducer does not make contact with the eyelid or create any pressure on the globe. This can be verified and documented during the examination by visualizing an anechoic gap on the ultrasound image between the transducer surface and the skin surface of the eyelid. Like any ultrasound examination, the amount of energy exposure of any tissue should be limited to what is necessary for the examination. This is especially true when using Doppler ultrasound. PWD in particular is of higher intensity than normal B-mode ultrasound. Modern diagnostic ultrasound machines are manufactured with a maximum output power that is very unlikely to produce heating or damage to the tissues; however, there are no long-term data available with regard to the absolute safety of ocular ultrasound.

2. Inadequate amount of gel. Ultrasound gel is essential for an adequate examination and should be used liberally. The gel acts as a medium to couple the transducer to the skin surface, decreasing the impedance between these two interfaces. When an inadequate amount of gel is used, artifacts are more frequent and image quality deteriorates. Furthermore, the clinician may be tempted to push harder on the globe to increase contact. With a perforated globe, this can exacerbate the injury.

3. Confusing pathology. In clinical practice, there can be overlap in sonographic findings among various retinal abnormalities. A retinal detachment can be confused on ultrasound with a posterior vitreous detachment. Both have similar initial presentations. However, posterior vitreous detachments are often a benign process, whereas a retinal detachment can be an ophthalmologic emergency. The development of a fixed visual field deficit suggests retinal detachment. The presence (retinal detachment) or absence (posterior vitreous detachment) of tethering of the membrane to the margins of the optic disc can also be very helpful for differentiating these two entities.

4. Retinal tears. Ocular ultrasound is more sensitive than direct visualization for the detection of retinal detachments. This is also true for the detection of vitreous hemorrhage. However, retinal tears can be quite small and difficult to locate. Therefore, when the history is indicative of a retinal tear or detachment, but none is visualized using ultrasound, the emergency physician should consider ophthalmologic consultation or urgent referral.

Case 1

Patient Presentation

A 32-year-old woman presented to the ED from the scene of a motor vehicle crash. She was intoxicated and was the unrestrained driver of a car that collided head on with another car. The patient was unconscious and hypotensive on arrival despite 3 L of IV crystalloid en route. Shortly after the primary survey, a trauma ultrasound examination was performed and showed a large amount of free intraperitoneal fluid. Obvious facial trauma and a midface fracture were noted just prior to endotracheal intubation. The pupils were 6 mm and sluggishly reactive bilaterally. There was concern about the possibility of severe head injury, but the trauma surgeon wanted to take the patient to the operating room immediately.

Management Course

An ocular ultrasound examination was performed and revealed normal ocular structures. The optic nerve sheaths measured 6.4 mm on the right and 6.3 mm on the left. Given this information, the trauma surgeon elected to obtain a head CT while the patient received a rapid blood and plasma infusion. Head CT showed a large epidural hematoma and the neurosurgeon joined the operating team. The patient was found to have a large splenic laceration and her spleen was removed. The epidural hematoma was evacuated. Despite repeated setbacks and two more trips to the operating room, the patient recovered, left the hospital 5 weeks later, and was able to care for herself and resume her office job.

Commentary

Case 1 illustrates a very high-risk and unstable patient. Risking a trip to the radiology suite for CT could have been disastrous if the patient had uncontrolled intraperitoneal hemorrhage. However, an expanding epidural hematoma would also have rapidly led to the patient's demise if not treated expeditiously. A rapid and noninvasive evaluation of intracranial pressure through optic nerve sheath measurement allowed the treating physicians to suspect a space-occupying lesion that required immediate attention.

Case 2

Patient Presentation

A 35-year-old man presented to the ED with complaints of left visual difficulties. He stated that for the last 12 hours his vision in the left eye had been considerably worse than before. He was not specific about any deficits. He denied trauma or prior visual problems. He did not wear glasses and denied any other medical problems.

Management Course

Visual acuity testing revealed 20/200 vision in the left eye and 20/20 in the right eye. Ophthalmoscopic examination showed a normal-appearing fundus and generally normal-appearing retina. No detachment was noted. A point-of-care ultrasound examination was performed on the affected eye. The anterior chamber and lens appeared to be normal. The retina was obviously detached on the nasal side of the eye with the central portion extending toward but preserving the macula. An ophthalmologist was contacted. The ophthalmologist examined the patient in the ED, reviewed the ultrasound images, and agreed with the diagnosis. The patient was taken to the ophthalmology suite for urgent repair of the retinal detachment.

Commentary

Case 2 demonstrates how ocular ultrasound can significantly add vital information in the ED. The globe is an ideal organ to scan, and ophthalmologists rely heavily on ocular ultrasound in many cases. A rapid and reliable diagnosis can be made.

Case 3

Patient Presentation

A 59-year-old diabetic woman presented to the ED complaining of waxing and waning vision in her right eye. It started approximately 12 hours before the presentation. The patient denied any similar symptoms in the past. She had not had any facial or head trauma. The patient did not wear corrective lenses and normally had good vision. Physical examination revealed 20/20 vision in the left eye with normal fields. With the right eye the patient was only able to see light and some general shapes, but could not read the Snellen chart. There was no tenderness on palpation of the globe, corneal staining did not reveal any abnormalities, and intraocular pressures were normal.

Management Course

An ocular ultrasound examination was performed and showed no structural abnormality in the right eye. The lens was in good position and there was no retinal or vitreous detachment. Color Doppler interrogation posterior to the globe revealed blood flow in the area of the central retinal vein and artery. However, only one color (blue) was noted and denoted flow away from the globe (Figure 19-26). PWD was added and showed an obvious venous tracing but no arterial flow could be located. The ophthalmologist was consulted and agreed with the diagnosis of central retinal artery occlusion. The patient was treated urgently by the ophthalmologist and regained partial vision.

Commentary

Case 3 demonstrates the expanded diagnostic capability of the ocular ultrasound. Structures posterior to the globe lend themselves readily to color and power Doppler interrogation as well as evaluation with pulsed Doppler, allowing for confirmation of appropriate blood flow to and from the eye.

The authors thank Dr. Michael Blaivas for his contribution on the previous edition of this chapter.