title: Eye muscle force development and saccadic velocity in thyroid-associated ophthalmopathy.
abstract: BACKGROUND
  Ocular motility disturbances are very common in patients with thyroid-associated ophthalmopathy (TAO). The force duction test has demonstrated that limitations of eye movements may be caused by mechanical restrictions in the muscles. A quantitative evaluation of isometric force production and ocular motility in all directions of gaze could further elucidate the mechanism of the movement disorder.
  
  
  METHODS
  In eight patients with TAO and eight controls of the same age range, horizontal and vertical saccadic movements of both eyes were recorded by means of electro-oculography (EOG). The corresponding force development in muscles of the more affected eye in patients and the non-dominant eye in normals was measured, using a suction contact lens/strain gauge technique.
  
  
  RESULTS
  Steady-state tension in the patients was increased in all directions of gaze both horizontally and vertically, most markedly for vertical fixations in the upper field of gaze. However, peak tension was increased only for the downward movements in the upper field of gaze and for the horizontal movements in the abduction field of gaze. Vertical saccadic velocity was slower than normal in downward movements, and horizontal saccadic velocity was reduced in the abduction field of gaze.
  
  
  CONCLUSIONS
  The increased active eye muscle tension in different directions of gaze could represent an adaptational mechanism of the ocular motor system to overcome the eye movement restriction in TAO.
authors.affiliation: Department of Ophthalmology, Huddinge University Hospital, Karolinska Institutet, 141 86 Stockholm, Sweden. suna.tian@klinvet.ki.se
authors.forename: Suna
authors.initials: S
authors.lastname: Tian
authors.forename: Gunnar
authors.initials: G
authors.lastname: Lennerstrand
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Nishida
authors.forename: Leif
authors.initials: L
authors.lastname: Tallstedt
mesh_terms: D000368:Aged; D004585:Electrooculography; D005260:Female; D006111:Graves Disease / Q000503:physiopathology*; D006706:Homeostasis; D006801:Humans; D007537:Isometric Contraction; D008297:Male; D008875:Middle Aged; D009801:Oculomotor Muscles / Q000503:physiopathology*; D012438:Saccades; D013997:Time Factors