Ocular Ultrasound

Indications

Ocular complaints constitute approximately 3 % of US ED visits. Ocular POCUS (point of care ultrasound) is ideal for patients presenting with:

  • Sudden decrease in vision or loss of vision
  • Ocular trauma +/- suspected foreign body
  • Sudden ocular pain
  • A concern for increased intracranial pressure

Key Ultrasound Anatomy

Documentation

At most 6 views to evaluate the posterior chambers, the retina, the retrobulbar area and the optic nerve:

Transverse Views
    1. Optic nerve
    2. Superior orbit
    3. Inferior orbit
Longitudinal Views
    4. Optic nerve
    5. Medial orbit
    6. Lateral orbit

Approach

  • Select the ocular preset mode to maintain the lowest possible energy exposure respecting the ALARA principle (as low as reasonably achievable). 
    • Option 1: Place a small Tegaderm directly over the closed eye. Apply a generous amount of ultrasound gel over the dressing.
    • Option 2: Apply a generous amount of sterile surgilube or ultrasound gel over the closed eyelid.
  • Scan both eyes in transverse (marker to the patient's right) and in longitudinal (marker points to top of the head) views.  Be sure to sweep the transducer from side to side in both planes to fully visualize the entire eye.  Start with the patient looking straight ahead. Then instruct the patient to look to from side to side for the kinetic (motion) exam. 

Probe & Positioning

  • 5 – 10 MHz linear vascular probe (best for superficial structures). If unavailable, the endocavitary probe may be used in a pinch, but is more awkward to hold and position.
  • Place a finger on the forehead or bridge of the nose to stabilize the probe. Allow the probe to "float" in the gel to avoid placing direct pressure on the ocular structures.
  • Supine/reclined pt with closed eyes. Do recline further than 45 degrees in a patient with suspected globe rupture.

Clinical Question & Exam Interpretation

  • Is there an ocular foreign body?
    • Positive: Hyperechoic object seen in the vitreous.  Typically highly reflective objects with "twinkling" artifact on color doppler. Shadowing or reverberation artifacts may also be seen. 
    • Negative: Echolucent vitreous
  • Is there vitreous hemorrhage?
    • Floaters, painless
    • Negative: Echolucent vitreous and uniform appearing posterior membrane
    • Positive: Increased areas of echogenicity in the vitreous fluid.  Blood may also layer inferiorly making differntiation between vitreous hemorrhage and retinal detachment difficult. "Swirling" motion like clothes in a dryer is apparent on kinetic exam.
  • Is there retinal detachment?
    • Curtain drop visual loss, painless
    • Positive: Hyperechoic rippled (or undulating/serpentine) membrane tethered anterolaterally to the ora serrata and posteriorly to the optic nerve.  Kinetic exam can differentiate retinal detachment from vitreous hemorrhage. The macula is lateral to the optic nerve on the retina in the direct  line of vision.  If the macula is still attached, but the attachment is threatened, emergent ophthalmologic consult is indicated to preserve high acuity vision.
    • Negative: Retinal layer that cannot be differentiated from the other choroidal layers.  No evidence of vitreous hemorrhage.
    • In a skilled operator, bedside ultrasound has 97% sensitivity and 92% specificity for retinal detachment.
  • Is there evidence of increased ICP?
    • Positive: Measure 3 mm back from the retina and then measure the optic nerve in transverse. If the diameter ≥  5 mm, it is concerning for increased ICP.  Also visualized as papilledema on fundoscopic exam.  In a skilled operator, ultrasound is 90% sensitive and 85% specific for detecting ICP >20 mmHg in traumatic head injury patients.
    • Negative: Optic nerve sheath diameter less than 5 mm
  • Is there lens dislocation?
    • Positive: often easily diagnosed with the lens being visualized in a non-anatomic position. Subluxation is harder to assess, but kinetic exam can help when the lens moves independently from the rest of the ocular structures.
    • Negative: anatomic position of the lens

Pearls and Pitfalls

  • Ocular ultrasound is contraindicated if there is apparent globe rupture! 
  • Avoid applying pressure to a traumatic eye injury, any pressure to the globe which could result in vitreous extrusion if an unrecognized globe rupture exists. Apply a generous amount of gel to a closed eye to avoid touching the eye with the probe.
  • Use of Tegaderm dressing avoids getting ultrasound gel in the eye, which can irritate ocular structures.
  • Consider turning up the gain when evaluating for vitreous hemorrhage, which can be missed if the gain is too low.
  • Beware of the oculocardiac reflex which is a vagal response when pressure is applied directly to the globe, resulting in bradycardia and in rare instances syncope.