Proptosis refers to forward protrusion of the globe with respect to the orbit. There are many causes of proptosis which can be divided according to location and it is worth remembering that it is not just orbital disease processes that cause proptosis.

Exophthalmos also describes forward protrusion of the globe. Several authors use the terms differently, which can be confusing:

  • proptosis and exophthalmos are often used interchangeably
  • exophthalmos used to refer to severe (>18 mm) proptosis 5
  • exophthalmos used to refer to endocrine-related proptosis 6

Enophthalmos is the opposite, displacement of the globe posteriorly.

The causes of proptosis is broad and includes a wide range of mass lesions that originate within the cranium, sinuses, paranasal spaces, and orbit 3:

Assessment of proptosis on cross-sectional imaging is difficult and dependent on the study being acquired in the correct plane:

  • the plane of the study must be parallel to the head of the optic nerve and the lens
  • the patient must have their eyes open and be looking forward with no eye movement

The reference line for measurement of proptosis is the interzygomatic line (a line is drawn at the anterior portions of the zygomatic arches):

  • the distance from this line to the posterior sclera is normally 9.9 +/- 1.7 mm 2
  • the distance from this line to the anterior surface of the globe should be <23 mm 4

The thickness of the extra-ocular muscles can also be used 1.

MRI may also be used in evaluation due to its multiplanar and the inherent contrast capabilities. Use of MR prevents ionizing radiation to orbits. The imaging findings are similar as described above for CT.

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Article information

rID: 21196
System: Head & Neck
Section: Gamuts
Synonyms or Alternate Spellings:
  • Exophthalmos
  • Proptosis (differential)

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Cases and figures

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    Case 1: hyperthyroidism
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    Case 2: sphenoid wing meningioma
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    Orbital venous ma...
    Case 3: orbital venous malformation
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    Axial CT-scan con...
    Case 4: thyroid orbitopathy
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