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7.06: Zone O4 – Medial Canthal Line at Inferior Orbit

YOUR ASSIGNMENT FOR THIS LESSON

✅ Step #1: Review all content below.

✅ Step #2: Image the O4 zone on your own with your ultrasond, and using the checklist provided on this page, check off all key structures to be identified in this location

TRANSDUCER POSITION AT O4

STANDARD O4 ORIENTATION:
LONGITUDINAL

Intersection of the medial canthal line and horizontal O3 line is the O4 position

QUICK TIP
  • Locate the bone of the orbital rim first to determine your optimal depth of imaging. 
  • Superior to the orbital rim will be the orbital fat and globe of the eye.
  • A hypoechoic structure superficial to this bone will be the orbicularis oculi muscle.
  • Deep and inferior to the orbicularis oculi muscle will be the LLSAN muscle.
    • Angulating the probe slightly to the contour of the nose can make the LLSAN and angular artery easier to visualize. (See animation above)
  • Once you feel comfortable with the orbital standardized views/positions, it is suggested that you scan in the longitudinal position directly from O3 to O4 to appreciate the entire anatomy of this area.

EXAMPLE OF IMAGE ACQUIRED AT O4

Standard image acquired at O4. Right O4 Position (Longitudinal with slight medial angulation | Left side is deep). See key below for lables.*

ANATOMICAL LEGEND FOR O3 LOCATION IN LONGITUDINAL

*Standard image acquired at O4 labeled with key anatomical structures.

DOPPLER IMAGES ACQUIRED AT O4 OF KEY VESSELS

Play Video
QUICK TIP
  • The critical artery to identify here is the angular artery. It will often be slightly medial to the O4 position and its depth can be variable.
  • Lateral to the angular artery you will find another large vessel, the angular vein. Scan between O3 and O4 to identify the vein laying more lateral and the artery coursing more medial. 
  • To optimize the visualization of the angular artery, angulate the probe in the longitudinal position along the contour of the nose. You will see more of the artery at once as it travels in a slightly diagonal course in this direction.

DO IT YOURSELF CHECKLIST

Structures to Identify on Ultrasound for O4

Once you have completed this checklist, mark this part of the lesson as complete.