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 ...