Ophthalmologic complaints comprise 2%–3% of all emergency department (ED) visits. Many of these complaints can be diagnosed by history and physical exam in conjunction with an ophthalmoscope or a slit lamp. Bedside ocular ultrasound may be used adjunctively with these traditional diagnostic methods in making the diagnosis and may add information that is difficult to obtain via other methods.
Ocular ultrasound has been performed by ophthalmologists for nearly half a century. Recently, due to increased access to machines and adequate training, emergency and critical care physicians have adopted this technology. While acute eye complaints are more common in the emergency department setting, ocular ultrasound may also be of use in evaluating intracranial pressure in the ICU setting.
The eye is a fluid-filled structure; therefore, ultrasound is an ideal diagnostic modality. Sonography provides a noninvasive method of evaluating the entire globe. It can be used in both traumatic and nontraumatic eye disorders.
Bedside ocular ultrasound should be performed in the following patients:
- The patient with an acute change in vision
- The trauma patient presenting with penetrating or blunt injury to the orbit or eye when globe rupture is not suspected
- The patient with atraumatic eye pain
- Patients with suspected increased intracranial pressure
The only absolute contraindication to bedside ocular ultrasound is suspected globe rupture.
Linear Probe with a Frequency of 7.5–15.0 MHz
Higher-frequency probes, which provide better resolution, are preferred for ocular ultrasound. These probes provide superior resolution for ocular imaging, as the eye is a superficial structure. In fact, while higher-frequency probes are typically not available in the ED or critical care settings, ophthalmologists may use probes with frequencies of 20 MHz or higher, which may provide superior images of the anterior chamber and retina.
Visualizing the small structures of the eye can be challenging. The sonographer should attempt to utilize as much of the screen as possible by adjusting the depth imaged. By decreasing the depth, the globe will take up most of the screen and this will allow the operator to better view the areas of interest.
The zoom tool may be used to help magnify the image and to better focus in on the area of pathology.
Adjusting the focal zone to the area of interest will improve the lateral resolution of the image and can aid in identifying abnormal structures.
Initially, the overall gain on the machine should be turned down in order to better visualize the anechoic aqueous and vitreous humor. After interrogating the entire orbit at a lower setting, the overall gain should then be slowly increased. This adjustment in gain will increase the brightness of structures that are transmitted on ...