The Eye As A Joint: Toward A Global View of Orbital Biomechanics – Part 1


The eye is a specialized joint adapted for sight.  Its pivoting nature within the globe, as an eyeball in the orbit, renders it as a non weight-bearing, ball-in-socket joint. While many visual anomalies we deal with go well beyond the eyeball, downplaying the local constraints and role of the eyeball comes with its own risks that verge on oculomotor fundamentalism.

 

Eyeball Fat

 

The term “duction”, meaning rotation of the eye, stems from a more global origin within the skeletal system of the body.

Circumduction

 

Tendons, sheaths, ligaments, pulleys, capsules, and fat pads found within the orbit of the eye are all basic accessory joint structures, and in particular are properties of synovial joints that require significant lubrication.  The eye, in fact, is the only joint space in the body that is directly exposed to air, so that its need for lubrication is at a premium.

Orbit

 

This is why treatment for dry eye disease (DED) now incorporates the same lifestyle recommendations for controlling inflammation and dryness in rheumatology – bolstering the visco-elastics from within (increasing fluid intake, omega 3 fatty acids, cod liver oil, fresh fish, exercise, etc.) intend of primarily dumping in evaporative drops externally.  In other words, ocular surface disease (OSD) often has its origins beneath the surface, and the latest formulations of drops and gels contain hyalruonic acid, a basic ingredient in the synovium.  It is no coincidence that terms used to describe wear and tear of the anterior segment, such as pannus and erosion, stem from rheumatology and in particular synovial joints hinged on visco-elastics.

 

Synovium

This is merely the food for thought that will launch us into orbital biomechanics, with its integral role in monocular and binocular control, in Part 2.

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