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Ocular anatomy

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Video 14-01: Ocular anatomy

The ocular anatomy can be identified in this video. Notice the soft tissue at the top of screen shows no sign of compression, and there is even a small pocket of uncompressed gel at the top right side of the screen. This is important to not put pressure on the eye. The lens can be seen anteriorly, followed by the anechoic vitrea. At the bottom of the screen, the retina is bright due to posterior acoustic enhancement, but the dark shadow of the optic nerve sheath can be seen as the operator fans through the eye.

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Hand positioning

Ask patient to look straight ahead; stabilize hand on patient's nose, malar bone, or forehead (if scanning from head of bed) to avoid pressure on globe.


Measurement of optic-nerve sheath diameter (ONSD)

Measure the ONSD 3 mm posterior to the globe; normal diameter, <5.0 mm.

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Video 14-02: Increased optic nerve sheath diameter (ONSD)

In this video, good low pressure technique is again demonstrated. The optic nerve sheath is larger, however, than in the previous video. Using the freeze frame and caliper functions on the machine are essential to make the precise measurements of the optic nerve sheath diameter.

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  • Indications for exam: ocular trauma, sudden vision changes, concern for increased intracranial pressure or foreign-body.

  • Probe selection: high-frequency linear probe.

  • Use the ocular setting if available. In addition to image optimization, this preset reduces power to 50% to minimize the risk of retinal damage.

  • When prepping the patient for the exam, a clear plastic adhesive dressing may be used. Gel placed on the outside of the dressing decreases the likelihood of gel entering the eye. We do not recommend this technique because air bubbles may be trapped under the dressing, there is a greater likelihood of applying pressure to the globe, and there may be eyelid or eyelash trauma with removal of the adhesive dressing.

  • Apply gel generously so that images are obtained without actual contact with the skin. The footprint of the probe and curved surface of the globe can make maintaining contact without applying excessive pressure challenging.

  • Stabilize hand on a boney structure: nose, forehead, or malar bone of cheek.

  • Image in both transverse and sagittal planes.

  • Ask patient to look right and left as well as up and down if concerned for hemorrhage or foreign body.

  • The optic nerve is a dark, well-demarcated tubular structure that arises ...

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