Ocular Injury Evaluation With Bedside Ultrasonography

Every year, approximately 1 million patients present to emergency departments (ED) in the United States with ocular injuries.[1] These presentations range from obvious penetrating trauma to more subtle acute vision changes without a readily discernible source. Unfortunately, in many centers, ophthalmologic consultation is not available in-house, and computed tomography (CT) scanners are notoriously busy, which delays the time to diagnosis and treatment.

Although not a typical imaging modality used by acute care clinicians for ocular complaints, bedside ultrasonography is increasingly available and can rapidly detect certain types of ocular pathology.[2, 3]

Ocular bedside ultrasound can help diagnose retinal and vitreous hemorrhage, retinal and vitreous detachments, ocular infections, foreign bodies, retrobulbar hematoma, and ocular vascular pathology. In addition, it can measure optic nerve sheath diameter to assess increased intracranial pressure.[4, 5, 6]

In comparison to formal CT or ophthalmology consultation, bedside ultrasonography has proven to be highly accurate and readily able to identify findings that need referral and additional workup.[7, 8]  Studies have reported ultrasound specifity ranging from 82.35 to 99.7% and sensitivity above 42.55 to 97.8% depending on diagnosis.[9, 10]

Case reports have described the effective use of emergent ocular ultrasonography in extreme settings such as combat hospitals[11] and even during space missions.[12]

In patients with suspected globe rupture, the amount of pressure exerted on the eye must be limited to prevent any further damage.

If the globe appears ruptured on external inspection, the risk of further pressure from a bedside ocular ultrasonographic examination may outweigh the potential benefits. Use caution and give careful clinical consideration before proceeding.

The following conditions may be further evaluated with bedside ultrasonography:

• Acute changes in vision

• Spontaneous intraocular hemorrhage

• Lens dislocation

• Retinal artery or vein occlusion

• Retinal detachment

• Suspected elevated intracranial pressures (ICP)

Closed eyelid examination allows for increased patient comfort and is necessary for patients with significant ocular swelling. Examination through a closed eyelid, however, results in a small and often inconsequential loss of image resolution. In certain situations, an open eye examination is more helpful, if the patient can tolerate it.

The placement of a sonolucent adhesive such as Tegaderm over the closed eye decreases the risk of conjunctival infection. It also increases the patient’s comfort by avoiding direct contact of the gel with the eyelid surface.

Applying liberal amounts of gel to the eyelids allows the examiner to minimize the amount of pressure exerted on the eye. This results in increased patient compliance and a better examination.

If too much pressure is exerted, the cornea may begin to flatten out. The goal is to use minimal pressure and to maintain normal corneal convexity.

Setup

Arrange the equipment at the bedside, with the ultrasound machine positioned close to the patient’s head to allow for easy access.

Start with the linear array transducer set at a frequency between 7.5 and 10 MHz. The eye structures are superficial, which allows for the use of this high-frequency probe.

Position the patient as noted and clear the area of examination.

Instruct the patient to close his or her eyes and then apply a liberal amount of ultrasound-conducting gel over both lids.

Instruct the patient to fix his or her eyes on a distant point in order to limit the amount of eye movement during the examination.

Procedure

Position the probe in a transverse orientation, with the probe marker to the operator's left, taking special care to minimize the amount of pressure exerted on the eye.

Adjust the positioning of the probe until the anterior chamber and the lens are visible.

Gently scan in a cephalad-to-caudad direction until the full anatomy of the eye has been visualized.

Rotate the probe clockwise 90° and scan side to side (lateral to medial), ensuring that all aspects of the eye have been imaged.

Much discussion has focused on the use of ocular ultrasonography to assess for the presence of increased intracranial pressure (ICP).[13]  This is performed by measuring optic nerve sheath diameters (ONSD). The optic nerve sheath diameter is best measured in the coronal axis versus the visual axis.[14] As one scans posteriorly, the visual axis is consistently larger than the coronal axis; this is the result of artifactual shadowing rather than true nerve sheath diameter measurement.[4, 5]

With the probe positioned at the lateral canthus and the beam directed nasally, measurements should be made in a superior-to-inferior orientation perpendicular to the nerve sheath diameter, at a distance of 3 mm behind the globe.[15]

The video below depicts a demonstration of an ocular examination.

Image interpretation

A normal eye shows a convex cornea, an anteriorly positioned lens, and a continuous retina, as depicted below.

The retina is usually not seen unless it is detached from the posterior chamber.

The lens has variable echogenicity but a characteristic biconvex shape.

The anterior and posterior chambers are filled with vitreous fluid and should be anechoic.

The optic nerve sheath can be visualized as a hypoechoic line originating from the posterior globe.

Foreign bodies may be detected within the globe, but visualization depends largely on the intrinsic echogenicity of the foreign bodies. Metallic objects are especially visible, whereas materials such as wood are more difficult to discern. In some cases, hemorrhage may also be present.

Hemorrhage may be either intrabulbar or retrobulbar. A retrobulbar hematoma appears as a predominantly hypoechoic self-contained space, deep to the retina. An intrabulbar hemorrhage appears as echogenic blood within the globe. Depending on the amount of blood, the globe may show stringing of leaking blood or may be completely filled.

Retinal detachment, shown below, appears as a hyperechoic rim or flap that has separated from the posterior aspect of the globe. Retinal detachment must be distinguished from a posterior vitreous detachment, which is thinner and still connected to the retina. Limited data support a high negative predictive value of ocular ultrasound for the detection of retinal detachment.[16]  In a meta-analysis of the diagnostic accuracy of ocular ultrasonography in patients who had retinal detachment from trauma, sensitivity ranged from 97 to 100% and specificity from 83 to 100%.[17]

A lens dislocation may present with the lens partially or completely dislocated from its normal anterior positioning. The lens may be found lying on the posterior aspect of the retina or hanging from still-connected zonule fibers. The lens is readily distinguished by its characteristic echogenicity and shape.

A ruptured globe may appear smaller than the contralateral globe. The normal shape and curvature of the eye may also be distorted. Secondary hemorrhage is frequently present.

Elevated intracranial pressure can cause edema and swelling of the nerve sheath. In both adult and pediatric cases, an optic nerve sheath diameter (ONSD) greater than 5 mm has been associated with an increased ICP.[18]  In a study by Mathews et al, bedside evaluation of ONSD accurately predicted raised intracranial pressure (RICP) in traumatic brain injury patients in the ED.[19]

The video below depicts abnormal ocular findings.