Bround Sound: Ultrasound to Assess Extraocular Movements and Pupillary Light Reflex
By Meagan Kozhimala and Kristin Dwyer, MD
The assessment of extraocular movement (EOM) and pupillary light reflex can be used to evaluate for ocular injury post-trauma. However, many patients with ocular trauma can present with significant orbital edema or pain that limits assessment due to the physician being unable to retract the eyelids. Ocular ultrasound provides a unique way to assess the eyes in the event of a trauma without causing significant pain or harm to the patient. This blog post provides techniques on how to perform ocular ultrasound to assess EOM and pupillary light reflex.
The patient can be in supine or recumbent position. With the eyelid closed, a non-adhesive sterile dressing, such as a tegaderm, can be placed over the eye to protect it, ensuring to smooth out any air bubbles (air can affect the sound waves). A copious amount of gel is applied over the closed eye and a linear probe is used with frequency of 10-13 MHz. The probe is placed in the transverse plane, indicator toward patient’s right, with the operator’s fingers resting on patient’s nose or cheek to avoid excess pressure on the orbital globe.
Figure 1: Normal ocular sono-anatomy (Harries et al., 2010)
Figure 2: Positioning of the probe for ocular ultrasound
Once this image is achieved, the operator can ask the patient to move their eye in all four directions to assess EOM. Lack of movement can suggest entrapment of a muscle and can indicate the need for emergent ophthalmologic consultation. Click here to see what normal EOM looks like on ultrasound.
After assessing for movement, the operator can tilt the probe upward until a view of the iris with pupil is seen.
Figure 3: Normal Ocular Sono-anatomy with probe tilted (Harries et al., 2010)
Using the ultrasound calipers, the diameter of the pupil can be measured. The operator can shine light into the unaffected eye to assess for consensual pupillary constriction, which would indicate an intact cranial nerve III. Lack of pupil constriction can be linked to a severe injury needing urgent evaluation and intervention. The M-mode setting allows for measurement of the pupillary diameter over time (Sargsyan et al., 2009). Ultrasound assessment of pupillary light reflex for serial neuro exams has also been used (Harries et al., 2010). Absence of the pupillary light reflex has been shown to be a risk factor for mortality in the setting of craniofacial trauma (Sargsyan et al., 2009). A video of the pupillary light reflex can be seen here.
Given the importance of EOM and pupillary eye reflex in the setting of trauma, ultrasound can be an important tool for obtaining a physical exam, especially in the case of difficulty with opening eyelids. The use of bedside ultrasound can increase efficiency of diagnosis and help guide physicians in contacting the appropriate consults if emergent intervention is indicated.
Author: Meagan Kozhimala, MD
Faculty Reviewer: Kristin Dwyer, MD
References:
Harries, A., Shah, S., Teismann, N., Price, D., & Nagdev, A. (2010). Ultrasound assessment of extraocular movements and pupillary light reflex in ocular trauma. The American journal of emergency medicine, 28(8), 956-959.
Sargsyan, A. E., Hamilton, D. R., Melton, S. L., Amponsah, D., Marshall, N. E., & Dulchavsky, S. A. (2009). Ultrasonic evaluation of pupillary light reflex. Critical Ultrasound Journal, 1(2), 53-57.