ORBIT Neuroanatomy

Our eyes allow us to detect information about light and help to form complex this is how we're able to visualize the world around us and how you can see me right now but how do we compensate for changes in light intensity how do we control the focal depth of our lens the size of the pupil can actually adapt to changes in light the intensity it dilates in low light through sympathetic fibers.

It can constrict in high light intensity 

through parasympathetic fibers the complex machinery that regulates these functions travel through the orbit to the eyeball the orbits also contain muscles that move the eye and associated nerves and blood vessels let's look at the pathway of these nerves through the orbit to the eye here is the sketch of one of the orbits is seen from above this is medial and this is lateral the eyeball is where the optic nerve carries light information to the brain here is a branch of five the ophthalmic nerve, this important branch of the pelvic nerve is a nasal ciliary never.

Which carries general sensation 

from the eyeball through these ciliary nerves here this is cranial nerve three the oculomotor nerve which carries motor information to most of the muscles that move the eyeball cranial nerves four and six also innervate muscles that move the eye but we're not gonna talk about those here the oculomotor nerve also carries parasympathetic fibers remember these fibers will constrict the pupil and need to reach the constrictor pupil a muscle here they also innervate the ciliary muscle that focuses the lens let's follow the course.

These fibers are three to their target tissues 

preganglionic fibers carried in three leave the nerve and enter the ciliary ganglion which hangs off some of the ciliary nerves here they sign apps and postganglionic fibers follow the ciliary nerves into the eyeball to ultimately reach constrictor people they also reach the ciliary muscle sympathetic fibers to the eyeball are postganglionic they originate in the superior cervical ganglion at the base of the skull and follow the arteries into the orbit they hop off the artery onto these ciliary branches and follow them into the eyeball to reach dilator pupil eh let's have a look at these structures in a dissection of the orbit so this is a dissection of the orbit looking from above this is medial this is lateral and this is anterior you can see the eyeball and the optic nerve here is the nasal ciliary nerve and you can see it crossing the optic nerve to get to the medial side of the orbit.

Here is the inferior division of the 

oculomotor nerve or cranial nerves read preganglionic parasympathetic fibers leave cranial nerve three to enter the ciliary ganglion hereafter there synapse postganglionic fibers travel with the short ciliary nerves into the eyeball postganglionic sympathetic s' travel into the eyeball along these long ciliary nerves here pupil size is not solely dependent on light intensity an increased sympathetic tone will cause pupillary dilation for example when you're angry or scared or even in love clinically the assessment of pupil size is an important part of the neurological exam in particular when pupils are unequal in size this can give us important clues as to where a lesion causing these symptoms may be localized...