Orbit™ 1.8 on Intel® (OOI)

Orbit is a software tool that provides a user-oriented interface to a sophisticated biomechanical model able to simulate classical strabismus syndromes and data from individual cases, clarifying diagnostic and treatment possibilities in well-defined physiologic terms. You can now run Orbit 1.8 under OSX on your Intel Mac!

Orbit on Air

The Orbit™ 1.8 Gaze Mechanics Simulation remains* the most powerful, reliable, and informative simulation of ocular static mechanics and strabismus despite it's limitations (principally that it does not implement "coordinated EOM pulleys", but only "passive EOM pulleys", and so, may not behave correctly in tertiary gaze; see Miller (2007) for details).

When Apple introduced OSX in 2001, Orbit 1.8, being a "MacOS 68K" application, ran only in "Classic" emulation mode, and with OSX 10.5 (Leopard®), related to Apple's adoption of Intel processors, Classic disappeared. Orbit 1.8 on Intel (OOI) makes it possible to run Orbit 1.8 on modern OSX computers**.

If you study eye movement control, or treat strabismus, you will find Orbit and its related materials uniquely interesting.


Normal, Stiff, Short, Strong

Orbit 1.8 is a research and educational tool used all over the world by Ophthalmologists, Optometrists, and Orthoptists to model complex cyclo-vertical and innervational disorders and refine their diagnostic and treatment-planning skills, by researchers in vision and oculomotility to study orbital mechanics (eg, to distinguish orbital from central factors), by teachers to supplement the ophthalmology curriculum with strabismus simulation laboratories, and by students to consolidate loosely connected facts and observations into a solid sense of how the extraocular muscles work. 


Orbit analyzes extraocular mechanical (eg, globe dimensions, contractile forces, and muscle insertions, lengths, and stiffnesses) and innervational factors in eye alignment. It contains model eyes used to test suspected causes of motility disorders and proposed treatments, and a simulated eye alignment test, which shows how the model eyes behave, for comparison with clinical data or desired treatment outcomes. Orbit is related to the ophthalmotropes of Ruete (1845), Wundt (1862), and others, its main advantage being that its behavior is constrained only by knowledge of orbital mechanics, and not by the materials and mechanisms feasible in a physical model. Orbit solves for forces, innervations, and other parameters, according to equations given, in part, by Robinson (1975) and Miller and Robinson (1984).


Install OOI (new version for OS X 10.11, El Capitan)

Orbit 1.8.1 Download

  • Download Orbit 1.8.1 on Intel.
  • Un-archive Orbit181-on-Intel.zip to get the "OOI™ 1.8" application, and "OOI™ 1.8 - ReadMe in OSX".
  • Drag "OOI™ 1.8" to the Applications folder.
  • Open "OOI™ 1.8".
If you are stopped by an alert about Orbit 1.8 not being from a registered developer, you may set: “System Preferences » Security & Privacy » Open Anyway”.

Orbit will initially function in "demonstration mode", operating normally, except that output functions (saving, exporting and printing) will be disabled. You may find this sufficient for your purposes. If you previously purchased an Orbit 1.8 license, gain full functionality by entering your license information, as before. If you have lost your registration information, I can provide it.

Three kinds of online help are available within Orbit. Launch Orbit and read the explanatory documents in the Guide Menu . Click  for help with Orbit windows. Use (extensive!) Balloon Help (under the Help item on the menu bar) to explain labels, fields and other objects. The Orbit User's Manual and Release Notes are available for download below. If you've misplaced your registration code, I can provide it (jmm@eid...).

=> Recent changes to Google Drive appear to corrupt Orbit on download! If your download does not open properly, write me (jmm@eid...) and I'll send you the zip file. <=

Get the Orbit 1.8 User Manual

Orbit User Manual

Download the User Manual. Read about the research supporting Orbit 1.8 elsewhere on this site.

Watch Orbit Movies

Orbit Movies

These are QuickTime™ movies consisting of images produced with Orbit™.
  • Muscle Colors: Saturation is proportional to 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).
  • Soundtracks: The frequency of impulses in the audio track is proportional to Orbit's innervation value.
As you watch the movies, notice:
  • Muscle Pulleys: The sharp bends in rectus muscle paths near the equator of the orbit are effects of muscle pulleys, which stabilize the muscle paths relative to the orbital wall.
  • Reciprocal Innervation: Innervation can be heard to increase for agonists (muscles that are pulling) and decrease 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, it is possible for innervation to be constant while total force changes because other muscles have changed that muscle's length.
Normal Eyes

These movies show superior and anterior views of simulated normal eyes looking in various directions through primary position: 40 horizontally, 40vertically and, 57 in 45 oblique directions. One file contains the (silent) video, and the others  contain soundtracks representing the innervation of the named muscle, with a link to the common video:
    • Normal (silent).
    • Normal (LLR inerv).
    • Normal (LMR inerv).
    • Normal (LSR inerv).
    • Normal (LIR inerv).
    • Normal (LSO inerv).
    • Normal (LIO inerv).
Duane's Retraction Syndrome

Duane's 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's 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 to be a misinnervation syndrome involving disturbances of innervation to the lateral and medial rectus muscles of the same eye.
    • Duane's Type 1: The descriptive signs 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 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. Notice that total LR and MR forces in the normal right eye show the expected reciprocal relationship, in contrast to the abnormal situation in the Duane's left eye.
    • Duane's Type 2: The signs 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. Here, 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.
    • Duane's Type 3: (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. The simulation 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.

Orbit Versions 

Three versions of Orbit were widely distributed.

Download OOI Miller JM, Pavlovski DS, Shamaeva I (1998). Orbit™ 1.8 Gaze Mechanics Simulation. pub Eidactics, San Francisco.

Orbit 1.8 is a full binocular model, meaning that both fixing and following eyes can be arbitrarily abnormal. It is no longer necessary that the fixing eye have normal, ie Listing, torsion. A new Parameter Fitter helps match a simulated eye such that its fixation behavior matches matches clinical alignment measurements.

Miller JM, Shamaeva I, Pavlovski DS (1995). Orbit™ 1.5 Gaze Mechanics Simulation. pub Eidactics, San Francisco.

With v1.5 the fixing eye can be abnormal so long as it obeys Listing’s Law, that is, has normal torsion.

Miller JM, Shamaeva I (1993). Orbit™ 1.0 Gaze Mechanics Simulation. pub Eidactics, San Francisco.

* We worked intensively with UAR, and provided them with our source code, so their SEE++ application might replace Orbit 1.8. However, despite it's modern program structure and fine graphics, when we last examined SEE++ (2005) we found many problems, including that it did not contain a correctly implemented biomechanical model.

** OOI is built on "COI-4.0.1+", which is a version of "Chubby Bunny", which is a preconfigured version of "SheepShaver", which is a PowerPC Classic MacOS environment that runs under other operating systems, the later all being Open Source projects. Thanks to Steven M Archer, MD of University of Michigan for advice & help in configuring this emulation.