title: Orbital computed tomographic characteristics of globe subluxation in thyroid orbitopathy.
abstract: OBJECTIVE
  Axial globe subluxation may complicate thyroid orbitopathy. This acute event is defined by anterior displacement of the globe equator beyond the orbital rim, lid retraction behind the equator, and tethering of the optic nerve. The authors explored the factors leading to spontaneous globe subluxation in patients with thyroid orbitopathy.
  
  
  METHODS
  A clinical review.
  
  
  METHODS
  The medical charts and axial and coronal orbital computed tomographic (CT) scans of all the patients with spontaneous globe subluxation were reviewed. The patients were categorized according to their CT scans into type I ("lipogenic" variant) or type II ("myogenic" variant).
  
  
  RESULTS
  Four (0.1 %) of approximately 4000 patients with thyroid orbitopathy presented with spontaneous globe subluxation. All of these patients had increased orbital fat without significant enlargement of the extraocular muscles. Thus, they represent type-I thyroid orbitopathy.
  
  
  CONCLUSIONS
  Globe subluxation in thyroid orbitopathy requires compliance of the orbital soft tissues and extensibility of the extraocular muscles. These are characteristics of type-I orbitopathy. The increased fat content results in more compliance of the soft tissues, and the normal caliber of the muscles allows them to become more extensible. This permits the acute contraction of the eyelids posterior to the equator of the globe. Patients with type-I orbitopathy and extensive proptosis may be at relatively greater risk of having globe subluxation develop.
authors.affiliation: Department of Ophthalmology, Massachusetts Eye & Ear Infirmary, Harvard Medical School, Boston 02114, USA.
authors.forename: P A
authors.initials: PA
authors.lastname: Rubin
authors.forename: L M
authors.initials: LM
authors.lastname: Watkins
authors.forename: S
authors.initials: S
authors.lastname: Rumelt
authors.forename: F C
authors.initials: FC
authors.lastname: Sutula
authors.forename: R L
authors.initials: RL
authors.lastname: Dallow
mesh_terms: D000208:Acute Disease; D000273:Adipose Tissue / Q000000981:diagnostic imaging; D000328:Adult; D005094:Exophthalmos / Q000000981:diagnostic imaging* / Q000209:etiology; D005133:Eye Movements; D005260:Female; D006111:Graves Disease / Q000150:complications*; D006801:Humans; D008297:Male; D009801:Oculomotor Muscles / Q000000981:diagnostic imaging; D009915:Orbit / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed; D014792:Visual Acuity