A 4-year-old Belgian Shepherd was evaluated with a history of head trauma a few weeks before presentation. On the day following recovery, the dog developed the issue shown in the video. Neurological examination was normal. However whenever the dog was chewing, both third eyelids were noted to protrude. No discomfort was noticed when eating food or with manual closing/opening of the mouth.

MRI of the brain, ocular bulbi, retro-orbital regions as well as the optic nerves was normal as was CSF analysis.

The video below is strongly suggestive of trigemino-abducens synkinesis. Synkinesis describes a sydrome where one body part moves unintentionally when a voluntary movement is performed by another body part that is not normally innervated by that same specific nerve. When this dog chews you can see bilateral involuntary third eyelid protrusion and adduction of both eyes.

Read about a similar case was reported by clicking the button below.

It is presumed that atypical connections form between the abducens nerve controlling the lateral rectus muscle and the mandibular division of the trigeminal nerve controlling the muscles of mastication. As a result of this dysinnervation, activation of the muscles of mastication by mandibular branch of the trigeminal nerve leads to coordinated activation of the lateral rectus muscle, or vice versa. This condition can be congenital or acquired as suspected in this case as a result of the head trauma and despite the absence of MRI findings.

Courtesy of Dr. Frank Gold from Veterinary Specialists of Sydney, Australia.