10.26.11+-+Anatomy+of+the+Eye+and+Orbit

Eye


 * 1. Describe the bony orbit, and its orientation within the anterior skull.**

Paired cone shaped structures oriented posteromedially. Medial walls are parallel to each other and lateral walls are at a 90o angle each other. The base of the bony orbit is the rim, formed by the frontal, zygomatic, and maxilla. Four other bones contribute to the posterior surfaces: ethmoid, sphenoid, lacrimal, and palatine.


 * 2. Identify the following 9 major apertures of the bony orbit and identify structures that traverse them: optic canal, superior orbital fissure, inferior orbital fissure, infraorbital groove, infraorbital foramen and anterior and posterior ethmoidal arteries.**

Optic canal: CN II and ophthalmic a. Superior orbital fissure: CNs III, IV, V1, VI, and superior ophthalmic v. Inferior orbital fissure: Infraorbital n. (terminal branch of V2), a., and v.

Infraorbital foramen (and groove): along the floor of the bony orbit, the infraorbital n., a., and v. flow through the infraorbital groove until the exit the orbit via the infraorbital foramen Anterior ethmoidal foramen: Anterior ethmoidal n. (branch of V1) exits orbit medially via this foramen Posterior ethmoidal foramen: Posterior ethmoidal n. (branch of V1) exits orbit medially via this foramen

Rim of the bony orbit: surrounds the anterior surface of the eye and transmits infratochlear n. Fossa of the lacrimal duct: houses the lacrimal lake, the lacrimal papillae, lacrimal sac, and the nasolacrimal duct Supraorbital foramen: Supraorbital n. exits orbit via this foramen


 * 3. Describe the structure of eyelids, lacrimal apparatus, and conjunctiva.**

The anatomical synonym for eyelid is palpebral. There are three muscles of the eyelid: orbicularis oculi, levitator palpebrae superioris, superior tarsal muscle. The eyelids meet and are divided by the palpeberal fissure. The medial and lateral commisures are the points in the angles. The medial and lateral canthi are the angles that meet at the commisures.

The lacrimal apparatus includes the lacrimal gland that empties into the lateral portion of the eye. The tears run medially and empty into the punctum, a hole on the lacrimal papilla that opens into the lacrimal canaliculus. The tears then drain through the puncta, caniculi, lacrimal sac, nasolacrimal duct, and into the nasal cavity.

The conjunctiva is a 2 sided bag that attaches to the inside of the eyelash, heads posteriorly over the surface of the eye, turns around at the fornix and heads back anteriorly over the surface of the eye and ends again at the palpebral fissure.


 * 4. Name muscles that move the eyelid and extra ocular muscles that move the eyeball. Describe their origins, insertions, actions and innervation.**

Levator palpebrae superioris attaches to the bony orbit and to the superior tarsus of the upper eyelid. The innervation is provided by the superior branch of the CN-III. The action is elevate the upper eyelid. Orbicularis Oculi - palpebral portion is to blink. Orbital portion is to wink. Branches from CN - VII innervate it. Superior Tarsal Muscle - Sympathetic, smooth muscle innervation. Scared, wide-eyed look.


 * 5. Describe the structure of the eyeball.**

It's in 3 layers: fibrous (sclera and cornea) vascular (iris, ciliary body, and choroid) and neural (retina).

Sclera (white) is posterior 5/6 of fibrous and cornea is anterior 1/6 (translucent) Posterior to fibrous layer is the anterior chamber The iris (the colored/muscular part) is next moving posteriorly Next is the posterior chamber (lens is in posterior chamber) The ciliary body is next and that is continuous with the choroid laterally as it complete the sphere of the globe Posterior to the ciliary body is the vitreous chamber Then the retina.


 * 6. Describe arterial supply and venous drainage of the orbit.**

The principal arterial branch that subserves the bony orbit is the opthalmic a. (a branch of external carotid a.). It gives off four branches: central a. of retina (pierces optic nerve, goes to retina), anterior and posterior ciliary a. (supply the rest to globe), lacrimal a. (lacrimal gland), muscular branches (muscles). The anterior and posterior ethmoidal aa. also enter with the nn. of the same name, they subserve stuff. The superior and inferior opthalmic vein cross CN II superiorly and inferiorly, then exit the superior orbital fissure. Inferior drains into superior which drains into cavernous sinus.


 * 7. Describe optic nerve, optic chiasm and optic tract.**

Axons of optic nerve extend from retina through nerve to chiasm, through tract and into brain


 * 8. Describe the innervation of orbital structures provided by CNs III, IV, V1, V2, VI, VII and the carotid plexus.**

CN III: occulomotor n. innervates the rectus muscles (except for lateral), levator palpebral superiora, and oblique inferior. It also carries parasympathetic nerves to ciliary ganglion CN IV: trochlear n. innervate superior oblique CN V1: opthalmic n. does somatic sensory to the lacrimal gland (lacrimal n.), upper lid and conjunctiva (frontal n.), and nose and ethmoid air cells (nasociliary n.). Also sensory root of ciliary ganglion CN V2: maxillary n. terminates as the infraorbital n. that does somatic sensory of lower eye lid CN VI: abducens n. innervates lateral rectus CN VII: facial n. innervates parasympathetic secretomotor fibers to lacrimal gland Carotid plexus: sympathetics enter orbit via optic canal on opthalmic a., supply tarsal muscles and the sympathetic root of the ciliary ganglion.


 * 9. Describe the ciliary ganglion and its sensory, parasympathetic and sympathetic contributions.**

Three roots enter, only one synapses. Sensory enters and then passes through to innervate body of globe. Sympathetic enters and then passes to innervate the dilator pupillae muscles. Parasympathetic enters and SYNAPSES and supplies sphincter pupillae and ciliary muscles.


 * 10. Describe the sensory and motor fibers that subserve the corneal reflex and the pupillary light reflex.**

Corneal Reflex: causes automatic closure of eyelids by sending somatic sensation to brain via long and short ciliary nerves (CN V1), nasociliary n. (CN V1). Action is passed via branchial motor fibers from CN VII to orbicular is oculi.

Pupillary Light Reflex: Special sensory by CN II of bright light. Visceral parasympathetic motor by CN III via ciliary ganglion, synapsing, and post-ganglionic fibers via short ciliary nerves to the pupillary constrictor muscles constricting iris.