Ocular Sonography in the Emergency Room

Indications

• Altered or lost vision
• Ocular pain or trauma
• Suspected intraocular foreign body (FB)
• Headache or altered mental status (when elevated ICP is a concern)
• Head injury with facial swelling obscuring direct exam

• Roberts & Hedges' Clinical Procedures in Emergency Medicine, p. 1484
• Rosen's Emergency Medicine, p. 3626

Contraindications

• Known or suspected open globe: Rosen's states ocular US is contraindicated with confirmed globe rupture. Roberts & Hedges' takes a more nuanced position: if globe rupture is possible but not obvious, a careful no-pressure technique is justified because the benefit of rapid diagnosis outweighs the risk. If physical exam obviously suggests open globe, the procedure is discouraged due to the risk of vitreous extrusion.
• Excessive orbital or periorbital emphysema will obscure images.

Equipment and Setup

• Transducer: High-frequency linear array, 7.5-10 MHz or higher
• Use the ocular machine preset to minimize thermal bioeffects
• Place patient supine or semi-reclined
• Instruct patient to keep eyes gently closed, looking straight ahead, without clenching
• Apply a Tegaderm dressing over the closed eyelid (optional but helpful), then a copious amount of gel over the eyelid/dressing to form an acoustic window
• Stabilize the probe by resting the hand on the patient's forehead, nose bridge, or maxilla
• Use the no-pressure technique - barely touch the probe to the gel without compressing the eyelid
• Roberts & Hedges', p. 1485

Scanning Technique

1. Scan in orthogonal planes (transverse and longitudinal) with both low- and high-gain settings
2. Adjust depth to visualize the full globe and ~1 cm of the optic nerve posteriorly
3. Identify normal anatomy: anterior chamber, iris, lens (echogenic biconvex structure), vitreous (anechoic), retina, optic disc
4. Use kinetic echography: ask the patient to move gaze side to side - this helps differentiate retinal detachment (moves with the eye) from vitreous hemorrhage (remains horizontal/settles)

Normal anatomy showing anterior chamber (top), lens, and anechoic vitreous - Rosen's Emergency Medicine

Pathological Findings

1. Retinal Detachment

• Undulates with eye movement
• Tethered at the optic disc and ora serrata; the flap crosses the midline of the posterior pole (vs. vitreous detachment, which does not cross the optic nerve)
• Sensitivity ~92%, specificity ~91.4% when performed by emergency physicians
• False negatives occur when retinal detachment is mistaken for vitreous detachment or hemorrhage, often due to improper technique or insufficient gain

A: Normal. B: Retinal detachment. C: Ruptured globe - Rosen's Emergency Medicine, p. 415

• Rosen's Emergency Medicine, p. 900

2. Vitreous Hemorrhage

• Appears as echogenic debris within the anechoic posterior chamber
• Mild: scattered echoes. Severe: diffuse echogenic fill
• Does not move with eye movement (settles horizontally) - key differentiator from retinal detachment
• Hemorrhage may be evenly distributed or focal ("boat-shaped" pre-retinal hemorrhage in the subhyaloid space)
• If afferent pupillary defect (APD) is present alongside vitreous hemorrhage, suspect an underlying retinal detachment

A: Vitreous hemorrhage (arrow). B: Boat-shaped pre-retinal vitreous hemorrhage - Rosen's, p. 900

• Rosen's Emergency Medicine, p. 900; Tintinalli's Emergency Medicine, p. 1601

3. Retinal vs. Vitreous Detachment: Key Differentiators

4. Globe Rupture

• Look for loss of the normal spherical shape, collapse or deformity of the globe
• Associated findings: irregular contour, intraocular air, lens dislocation, posterior acoustic shadowing from intraocular FB
• US has 94% correlation with CT for orbital fractures

Globe rupture with lens dislocation - Rosen's Emergency Medicine

5. Intraocular Foreign Body

• Appears as a bright, hyperechoic focus with posterior acoustic shadowing or reverberation artifact
• Metallic FBs produce characteristic "comet tail" artifact
• Can be seen even when obscured on plain radiograph

6. Lens Dislocation

• Normal lens is a biconvex, strongly echogenic structure in the anterior chamber
• Dislocation: lens absent from expected location, may be visible in the vitreous posteriorly

Optic Nerve Sheath Diameter (ONSD) for Elevated ICP

1. Place linear probe over closed eyelid
2. Ask patient to deviate gaze ~10 degrees laterally (aligns nerve with the beam, avoids false widening)
3. Measure ONSD 3 mm posterior to the retina (best contrast and reproducibility at this point)
4. Obtain at least 2-3 measurements and average them
5. Measure both eyes

• Sensitivity 87-95%, specificity 79-100% for ICP > 20 mmHg at cutoff of 5.7-6.0 mm
• Differential for elevated ONSD: elevated ICP, anterior orbital mass, optic neuritis, trauma, cavernous sinus mass

ONSD measurement: calipers placed 3 mm behind the globe, measuring 5.3 mm in a head injury patient - Tintinalli's, p. 1601

Papilledema: optic disc swelling visible on ocular ultrasound - Rosen's Emergency Medicine

• Tintinalli's Emergency Medicine, p. 1601; Roberts & Hedges', p. 1485-1486; Rosen's Emergency Medicine

Complications

• Inadvertent pressure on a ruptured globe can worsen injury or cause vitreous extrusion
• Excessive scan time can exceed thermal exposure limits - use the ocular preset and minimize dwell time

Summary Table

• Rosen's Emergency Medicine, Chapters 34 & 57 (ocular US, retinal detachment, vitreous hemorrhage)
• Roberts & Hedges' Clinical Procedures in Emergency Medicine, Chapter 62 (bedside ED ocular US)
• Tintinalli's Emergency Medicine, Chapter 241 (ocular US, ONSD measurement)