It seems that most everybody has a great uncle twice removed who had an “glass eye” that did not move. Contrary to popular belief, most modern artificial eyes and scleral shells move quite well. Movement of the artificial eye is dependent on the movement of the tissue behind the prosthesis and the fit of the prosthesis to this tissue.
Movement could be broken into a couple different categories:
- Conversational Motility
- Moderate Motility
- Extreme Motility
Motility is the movement of the eye, it includes conversational movement and the movement of the eye all the way to the extremities. Most patients we see experience very good conversational motility. We consider conversational motility to be the horizontal and vertical movement of the prosthesis in the first 10 degrees in each direction. This is the most common movement of the eye, the quick darting movements we all make during interactions with others.
Moderate motility is movement past the 10 degrees of conversational motility, but movement that falls short of the extremities. The degree of motility of an ocular prosthesis is most dependent on the movement of the ocular tissue or ocular implant placed by the surgeon. A nicely placed orbital implant that is central in the orbital cavity and appropriately attached to the major ocular muscles, will be well positioned to provide very good motility. A second factor in motility is the fit of the prosthesis to the orbital implant. Erickson Labs Northwest utilizes the modified impression technique that provides the best possible junction between the front of the orbital tissue and the posterior of the prosthesis, allowing the best possible movement.
Extreme motility is the movement of the eye all the way to the extremities. Extreme motility is more rare due to the anatomical design of the eye socket and the necessary shape of the artificial eye. Extreme motility is often seen in patients wearing a scleral shell over a nice full sized or phthsical globe. Extreme motility can also be seen in patients fitted with a motility implant and integration system such as a titanium peg.
Blinking is the vertical movement of the eyelids, mostly the superior lid, to close and open again. While blinking is not motility, it is very important to the realism of an artificial eye. Blinking functions to wet the ocular surface creating a tear film, promote creation of tears from the eyelid glands, pumping excess tears to the tear ducts, and clearing the ocular surface of debris. Proper blinking is very important to the health of the anophthalmic socket and the normal appearance of an artificial eye.