Orbit™ Movies

Orbit movies are QuickTime movies, consisting of images produced with the Orbit™ Gaze Mechanics Simulation. They can be viewed on any computer that supports the Quicktime movie format; the Orbit application itself is not required.

Muscle Colors: Saturation of a muscles color is proportional to its total force: pure red, pink, and grey represent, high, intermediate, and zero forces, respectively (color variation within a muscle is "rendering", to give the muscles a 3-D appearance).

Click any of the icons below to download a ZIP archive containing several Orbit Movies and some documentation (all icons download the same archive). It will appear on your disk in the folder you have chosen for browser downloads.

Normal Eyes

Normal Eyes: These movies show superior and anterior views of simulated normal eyes looking in various directions through primary position: 40 horizontally, 40 vertically and, 57 in 45 oblique directions. There are 8 files: Normal (silent) is the video track common to all Normal Eyes movies. The file can also be played directly as a silent movie. The 6 remaining movie files contain soundtracks representing the innervation level of the named muscle (and an internal reference to the common video). Normal (LLR inerv) plays the common video file above, along with a sound track representing the innervation to the left lateral rectus muscle. Normal (LMR inerv) – left medial rectus innervation soundtrack. Normal (LSR inerv) – left superior rectus innervation soundtrack. Normal (LIR inerv) – left inferior rectus innervation soundtrack. Normal (LSO inerv) – left superior oblique innervation soundtrack. Normal (LIO inerv) – left inferior oblique innervation soundtrack.

As you watch the movies, note:

Muscle Pulleys: Note the sharp bends in the rectus muscle paths near the equator of the orbit. These are effects of muscle pulleys, which stabilize the muscle paths relative to the orbital wall.

Reciprocal Innervation: Inervation (the frequency of impulses in the audio track) increases for agonists (muscles that are pulling) and decreases for antagonists (muscles that are relaxing).

Total Muscle Force: Total muscle force is the sum of contractile muscle force (mostly dependent on innervation) and elastic muscle force (dependent only on stretch). Thus there might be cases in which innervation is constant and yet total force changes, because other muscles have changed that muscle's length.

Duane Syndrome

This is a congenital disorder in which eye muscles are abnormally wired to the brainstem. Each movie's sound track represents innervation of the perversely innervated left lateral rectus muscle.

Observation vs Theory: Von Noorden (1990) characterized 3 types of Duane Retraction Syndrome on the basis of clinical signs. It is another matter to determine the mechanism of each type, or even whether 3 mechanisms account for all cases. Orbit simulations show that all typical signs can be generated by assuming Duane's Retraction Syndrome to be a misinnervation syndrome involving disturbances of innervation to the left lateral rectus (LLR) and left medial rectus (LMR) muscles.

	Theory of Duane's Type 1: The descriptive signs of Duane 1 are: (1) very limited or absent abduction; (2) protrusion of globe on attempted abduction; (3) normal or slightly limited adduction; (4) globe retraction on adduction; (5) frequently, up-shoots or down-shoots on adduction. Signs 1 and 2 and, of course, the anatomic findings of Hotchkiss et al (1980), suggest that the abducens nucleus is not functional. Signs 3 and 4 suggest that, on the affected side, the medial rectus branch of the oculomotor nucleus is providing partial innervation to the LR.The Orbit simulation eliminates the left abducens nucleus, and supplies 50% of the innervation from the left MR branch of the oculomotor nucleus to the RLR. We further supposed that chronic stretching of intermuscular tissues, and chronic compression of posterior orbital fat reduced their stiffness. In the movie, the normal right eye looks 40 along the horizon. Note that in the normal right eye total LR force and total MR force show the expected reciprocal relationship, in contrast to the abnormal situation in the affected left eye.
	Theory of Duane's Type 2: The signs of Duane Type 2 are: (1) Normal or slightly limited abduction; (2) Limited or absent adduction; (3) Globe retraction on attempted adduction; (4) Frequently, up-shoots or down-shoots on adduction. In this case, our theory is that abducens innervation of LLR is normal, accounting for sign 1, but that the LMR branch of the oculomotor nucleus is providing partial (75%) innervation of LLR, accounting for signs 2, 3 and 4.
	Theory of Duane's Type 3: Duane Type 3 is characterized by: (1) Limited or absent abduction; (2) Limited or absent adduction; (3) Globe retraction on attempted adduction; (4) Frequently, up-shoots or down-shoots on adduction. This simulation of Duane Type 3 is like that of Type 1, except that 100% (instead of just 50%) of the innervation normally supplied to LMR is supplied also to LLR.