Orbit Flashcards
What is the function of lacrimal gland and nasolacrimal duct?
The lacrimal gland has 9-13 openings that allow tears to be secreted into the conjunctival sac, keeping the cornea and conjunctiva moist/ friction-free. The nasolacrimal duct receives fluid from the punctum and then opens into the nasal cavity under the inferior concha on the lateral wall.
What is the function of the tarsal gland?
The tarsal glands secrete a fatty substance that keep the lids from sticking together when they are closed.
What is the common tendinous ring (annular ring)?
The common tendinous ring is at the back of the orbit and is where all of the rectus muscles of the eye originate from.
How would you specifically test each muscle for integrity?
There is a series of eye movements that allow for each of the muscles to be isolated. The eye must be aligned in the line of pull.
ABduct the eye: Superior rectus is the only muscle that can elevate the eye, inferior rectus is the only muscle that depress the eye.
ADduct the eye: Inferior oblique is the only muscle that elevate the eye, superior oblique is the only muscle that can depress the eye.
What is extorsion/intorsion? Which muscle(s) are responsible for extorsion/intorsion? What is the function of these movements (extorsion/intorsion)?
Intortion: eyeball rotates toward nose (superior oblique w/ minor contribution from superior rectus)
Extortion: Eyeball rotates away from nose (inferior oblique w/ minor contribution from inferior rectus)
The reason for these movements is that the yes rotate to compensate for tilt of the head to prevent double vision.
Which layer of the eye contains the photoreceptor cells?
The internal (retinal) layer contains the photoreceptor cells.
What is the macula lutea?
The macula lutea is a yellowish oval area lateral to the optic disc. It has a spot in the center that is depressed called the fovea centralis, which is the most acute area of vision.
What are the ciliary processes and their significance to vision?
The ciliary processes secret aqueous humor. This watery fluid drains away at the iridio-corneal angle (filtration angle) and then into a circular venous canal (of Schlemm). If filtration is blocked Glaucoma can result.
What are the 3 major branches of V1 in the orbit? What is/are the major modalities of all 3 of these
branches?
V1 is the opthalmic division of the trigeminal nerve.
It divides into 3 main branches:
1) The frontal nerve, which terminates in the supratrochlear and supra-orbital nn. This nerve does sensory to forehean and anterior region of the scalp.
2) The lacrimal nerve is lateral and does sensory innervation to the lacrimal gland. Also postganglionic parasympathetic fibers will follow this nerve.
3)Nasociliary nerve is the medial branch of V1. It branches into the ant/post ethmoidal n., the long ciliary n., and the short ciliary n. The long ciliary nn. provide sensory innervation to the iris and cornea. The short ciliary nn. have sensory branches for the back of the eye that have passed through the ciliary ganglion.
What types of fibers do the long and short ciliary nn. carry?
The long ciliary nerves carry somatic sensory innervation to the iris and cornea. Sympathetics hitchhike on the long ciliary nerves to innervate dilator pupillae.
The short ciliary nerves carry sensory fibers to the back of the eye. There are parasympathetics and sympathetics traveling with the short ciliary nerves as well.
How does the lacrimal gland get its vasomotor (secretory) innervation? Where do the sympathetic
fibers come from? The parasympathetic fibers?
The preganglionic parasympathetic cell bodies are located in the superior salivary nucleus. Axons pass via CN VII through internal acoustic meatus. At the level of the geniculate ganglion they form the greater petrosal nerve. They re-enter the cranial cavity at haitus of greater petrosal nerve and then pass out via foramen lacerum. They join the deep petrosal nerve and synapse in the pterygopalatine ganglion. Postganglionic parasympathetics then hitch a ride on V2 and its zygomatic branch, then ride with the lacrimal nerve to the lacrimal gland.
The sympathetic fibers travel with the parasympathetic fibers in the zygomatic branch of V2.
Name two nerves/vessels that exit the orbit to supply the forehead and anterior scalp.
supra-trochlear nerve
supra-orbital nerve
Both of these nerves are branches of the frontal nerve, which is one of three branches of V1 of the trigeminal system.
What is a blow out fracture and how does it present clinically?
A blow out fracture is an indirect traumatic injury that displaces the orbital walls. These often present with intra-orbital bleeding, which causes protrusion of the eyeball.
What is ptosis? What can result in this condition?
Ptosis is drooping of the upper eyelid. This can be caused by oculomotor nerve palsy. In this palsy the superior eyelid droops because the action of orbicularis oculi (supplied by facial nerve) is unopposed by the levator palpebrae superioris .
What is the corneal reflex? What cranial nerves does it involve?
The corneal reflex is tested when the examiner brushed the cornea with a wisp of cotton. A normal response is a blink. Failure to blink could mean a lesion of cranial nerve V, however a lesion to CN VII could also impair this reflex.
