The Ocular Ultrasound Challenge

• Decreased or loss of vision
• Suspected ocular foreign body
• Ocular pain
• Eye trauma
• Head injury or suspected raised intracranial pressure

Ocular ultrasound should be performed by an appropriately trained and accredited practitioner. This is how its done:

• Use a high-resolution (e.g. 7.5 MHz or higher) linear array ultrasound transducer.
• apply a large amount of standard water-soluble ultrasound transmission gel to the patient’s closed eyelid so that the transducer doesn’t actually need to touch the eyelid.
• adjust ‘DFG’ — adjust depth so that the image of the eye fills the screen, adjust the focus as required and turn up the gain to achieve acceptable imaging (to assess the vitreous chamber the eye should be examined at both ‘moderate’ and ‘high’ gain settings).
• Scan both eyes in both the sagittal and transverse planes through closed eyelids.
• Ask the patient to ‘look straight ahead with eyes closed’, but without clenching the eyelids. While scanning ask the patient to ‘look’ up, down, left and right.

A normal eye!

The normal eye appears as a circular hypoechoic structure with the following structures:

• cornea — thin hypoechoic layer parallel to the eyelid.
• anterior chamber — filled with anechoic fluid and is bordered by the cornea, iris and anterior reflection of the lens capsule.
• iris and ciliary body — echogenic linear structures extending from the peripheral globe towards lens. Pupillary response can be assessed by shining a light in the fellow eye.
• lens — anechoic.
• vitreous chamber — filled with anechoic fluid in the young healthy eye.
• retina — cannot be differentiated from the other choroidal layers.
• retrobulbar area includes optic nerve, extraocular muscles and bony orbit —  the optic nerve is visible posteriorly as a hypoechoic linear region radiating away from globe. Doppler can be used to assess the central retinal artery.

Click here for diagram showing the key elements of ocular anatomy or here for a labeled ultrasound image from UltrasoundVillage.com.

• globe perforation
• retrobulbar hematoma or emphysema
• retinal detachment
• lens subluxation/ dislocation
• vitreous hemorrhage and hyphema
• intraocular foreign body

• decrease in the size of the globe
• anterior chamber collapse
• buckling of the sclera

Examples:

• Ultrasound for Emergency Physicians — Ruptured globe

• the lens is displaced from its normal position, either anteriorly or posteriorly.
• this may be a result of  trauma or occur in conditions like Marfan’s syndrome.
• other evidence of trauma, such as vitreous hemorrhage, globe rupture or retinal detachment may also be present.

The example below shows a traumatic posterior lens dislocation with an accompanying vitreous hemorrhage:

from ‘Radiology Picture of the Day’ (click image for source)

• bright echogenic acoustic profile of the foreign body
• shadowing or reverberation artifacts may be seen

Examples:

• Ultrasound for Emergency Physicians — Ocular foreign body

• A thick hyperechoic undulating membrane in the posterior/ lateral globe
• in total retinal detachments the folded surface attaches to the ora serrata anteriorly and the optic nerve posteriorly.

This condition is considered in Ophthalmology Befuddler 008 — A Curtain Descends.

Examples:

• Ultrasound for Emergency Physicians — Retinal Detachment
• Ultrasound Village — Retinal Detachment 1 and Retinal Detachment 2

Optic nerve sheath diameter (ONSD) correlates closely with ICP and can be measured using ocular ultrasound.

The normal optic nerve sheath is up to 5 mm in diameter. ONSD is higher in the presence of a raised ICP (>20 mmHg).

How to measure ONSD:

• take the measurement 3 mm posterior to the globe for both eyes (ultrasound contrast is high at this point and measurements are more reproducible)
• average two measurements
• suspect raised ICP if the average ONSD is >5 mm

The evidence:

• Kimberley et al (2008)
  — ONSD > 5 mm detects ICP > 20 cm H2O with a sensitivity of 88% (95% CI = 47% to 99%) and specificity of 93% (95% CI = 78% to 99%)
• Moretti et al (2009)
  — ONSD threshold of 5.2 mm as a predictor of ICP >20 mm Hg had sensitivity and specificity of 94% and 76%, respectively
• Rajajee et al (2011)
  — Optimal ONSD for detection of ICP > 20 mmHg was ≥0.48 cm with sensitivity 96% (95% CI 91-99%); specificity 94% (92-96%)

Examples:

• Ultrasound for Emergency Physicians — Dilated Optic Nerve Sheath

• Fine linear and granular appearing echodensities visible in the vitreous chamber when gain settings are ‘very high’. There is a swirling appearance when the patient moves his or her eyes.
• Unlike retinal detachment, vitreous detachment:
  — occurs in front of the optic disc and does not remained anchored to it.
  — lacks a thickened hyperechogenic membrane.

This condition is considered in Ophthalmology Befuddler 012 — Flashing and Floating.

Examples:

• Ultrasound Village — Vitreous Detachment 1

Compare the following video with the Ultrasound Village example — vitreous detachment may not be obvious unless you crank up to a ‘very high’ gain setting. Make sure you compare the vitreous images to the retinal detachment images in Q7.

From hqmeded.com on Vimeo.

• Fresh mild hemorrhages — small dots or linear areas of areas of low reflective mobile vitreous opacities
• More severe and older hemorrhages — blood organizes and forms membranes.
• Vitreous hemorrhages may also layer inferiorly due to gravitational forces.

This condition is considered in Ophthalmology Befuddler 012 — Flashing and Floating.

Ultrasound can also detect a hyphaema in eye trauma when the eyelids cannot be opened.

Examples:

• Ultrasound for Emergency Physicians — Vitreous hemorrhage
• Ultrasound Village — Small Hyphaema 1

From dave plummer on Vimeo.