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Thyroid Associated Orbitopathy
(TAO)
Classical Signs : TAO
A prominent stare.
Retraction of all four eyelids
Bilateral exophthalmos
Hertel exophthalmometer 25 OD, 28 OS,
base 108.
Tight orbits/reduced orbital resilience
Prominent congested scleral blood vessels
A visible rim of sclera on gentle eye
closure
Eye movements
Lid lag (persistent elevation of the upper
eyelid in downgaze) – von Graefe sign
Marked limitation of upward gaze
Mild limitation of downgaze
Restricted horizontal eye movements
Positive forced duction test
TAO – Limited Upgaze
Limitation of upgaze is due to tethering
of the eyeball in the floor of the orbit by
soft tissue changes.
Tethering of the eyeball inferiorly can be
confirmed by a forced duction test.
TAO
Duction Test:
Anesthetize the eye with topical
anesthesia
Push on the globe with a cotton tip swab
or
Pull with blunt tweezers to try to move eye
up.
Mechanical restriction - a positive forced
duction test.
Compressive Optic Neuropathy
Most serious complication
Crowding of the orbital apex by enlarged
ocular muscles
Present in 50% severe cases TAO
May require urgent orbital
decompression
Figure 1 Axial CT through the orbit without contrast
shows enlargement of the medial rectus muscle
bilaterally. Note that the tendinous insertion is spared.
Figure 2 The coronal CT (reformatted from axial data set)
without contrast shows enlargement of the medial rectus
muscle, inferior rectus muscle and upper muscle complex
on both sides.
Courtesy of Hugh Curtin, M.D.
http://www.lib.med.utah.edu/NOVEL