Nearly 3% off all visits to emergency departments in the United States involve ocular complaints. Bedside ultrasound has become an indispensable tool for both traumatic and nontraumatic eye complaints. While ocular ultrasonography is not a new concept, its application in the critical care setting is new. Traditional fundoscopic-based eye exams are not only difficult to perform in the acute care setting; they are notoriously unreliable in the setting of trauma. The physical exam of the eye requires controlled conditions and appropriate equipment not often found in the ICU. Intensivists can use familiar ultrasound-based principles to develop a limited ocular exam capable of ascertaining a rage of pathological conditions not previously detectable on a physical exam. The eye itself is a fluid-filled structure ideal for sonographic imaging. The use of ultrasound allows the provider to perform a detailed exam of the ocular structures without the patient opening his or her eyes. This limited sonographic exam allows the practitioner to evaluate ocular movement, the anterior chamber, the posterior chamber, and the retrobulbar space, including the optic sheath to assess intracranial pressure.
Sonographic Anatomy of the Eye
The eye and the surrounding orbit offer perhaps one of the most acoustically friendly areas of the body. The surrounding bony orbit should be intensely hyperechoic with a posterior shadow. The anterior cortex of the orbital bones should be smooth with a sharp edge and display no irregularity, which could be a sign of pathology. The globe itself should be round, completely anechoic with the exception of the anterior structures, and posterior acoustic enhancement should be apparent (Figure 28-1). The anechoic fluid-filled anterior chamber is easily identified along with the thin hyperechoic cornea, which lies just superior to this space. Inferior to the anterior chamber lies the hyperechoic iris. Just posterior to the iris the elliptical shape of the lens is noted. Behind the lens lies the large echo-lucent posterior chamber. The posterior portion of the eye is hyperechoic and is made up of several layers, including the retina, choroid plexus, and sclera as the outermost layer. The optic nerve and sheath travel posterior to the globe as is seen as a long straight anechoic nerve bounded by hyperechoic sheath (Figure 28-2).
Normal eye with optic sheath.
The eye is a delicate structure and requires the examiner to pay explicit attention to technique. The patient should be placed in the supine to semirecumbent position. If the patient is noted to have obvious globe rupture the exam should not be preformed at the bedside. A high-frequency (7.5–15 MHz) linear transducer should be used for the exam. Most ultrasound machines currently have ...