Orbit and Eye - SRS Flashcards
What are the bones of the orbit?
- Frontal
- Maxilla
- Sphenoid
- lacrimal
- ethmoid
- palatine
- zygomatic
What makes up the apex of the orbit?
lesser wing of the sphenoid, surrounding the optic canal
What makes up the base of the orbit?
- formed by the orbital margin and orbital opening
a. Orbital margin is formed by frontal, zygomatic, and maxilla bones.
b. Orbital margin is thickened to provide support and protection to the eyeball.
What makes up the roof of the orbit?
a. Frontal bone and some sphenoid – separates orbit from anterior cranial fossa
b. Fossa for lacrimal gland
What makes up the floor of the orbit?
a. Maxilla bone – separates orbit from maxillary sinus
b. Zygomatic bone
c. Palatine bone
What makes up the medial wall of the orbit?
a. Ethmoid bone
b. Lacrimal bone
c. Maxilla bone
d. The lacrimal fossa; houses the medial portion of the lacrimal system.
What makes up the lateral wall of the orbit?
a. Zygomatic bone
b. Sphenoid – greater wing
A massive zygomaticomaxillary complex fracture, or direct blow to the orbit may cause a rapid increase in intracranial pressure which could lead to?
An orbital blow-out fracture:
The thin orbital floor is fractured.
What can happen in severe comminuted fractures of the orbital floor?
What are clinical signs that this has happened?
The soft tissue may herniate into the underlying maxillary paranasal sinus.
- diplopia
- infraorbital nerve parasthesia
- enopthalmos,
- edema
- ecchymosis
Since the orbital margins are strong, where do most fractures of the orbit occur?
At sutures between bones
Malignant tumors originating in the sphenoidal and ethmoidal sinuses, middle cranial, or infratemporal fossa can erode through the thin walls of the orbit or pass directly through foramina.
What can happen as a result of this?
Tumors can compress the orbital contents, and may cause exophthalmos.
When a person starves, the eyes often become sunken in, (enopthalmos). Why is this?
Loss of orbital fat
What is the periorbital fascia continuous with?
a. Continuous with periosteal dura at optic canal and superior orbital fissure.
b. Continuous with the orbital septum anteriorly.
c. Continuous with muscular fascias of extraocular eye muscles.
The medial and lateral check ligaments attach to medial and lateral orbital walls. What is the function of these ligaments?
a. Limit abduction and adduction of the eye.
b. Prevent posterior retraction of the eyeball by the rectus muscles.
What are the glands associated with the eyelids?
- Tarsal (Meibomian) glands (sebaceous glands)
- Glands of Zeis (smaller sebaceous glands)
- Glands of Moll (sweat gland)
Glands of the eye may become obstucted and inflamed.. What can this lead to?
chalazion (meibomian cyst) or a hordeoum (cyst of eyelash glands)
What muscles are associated with the eyelids?
- Orbicularis oculi
- Levator palpebrae superioris
What is the impact of CN VII impairment on the eyelid?
- Eyelid cannot close completely due to loss of innervation to orbicularis oculi.
- The inferior eyelid tends to fall away from the eyeball and result in dryness and irritation of the cornea and sclera.
What is the innervation of levator palperbrae superioris?
CN III
What happens to the eyelids with impairment of CN III?
Inability to open the upper eyelid (ptosis)
Loss of sympathetic innervation to the head is what syndrome? How does this present regarding the eyelids?
Horner’s syndrome
ptosis
What are the structures associated with the conjunctiva?
- Palpebral conjunctiva – epithelium of internal eyelid
- Bulbar conjunctiva – outer epithelium of sclera
- Conjunctival sac – between palpebral and bulbar conjunctiva; opens at palpebral fissure.
- Conjunctival fornices (superior and inferior) are formed where bulbar and palpebral conjunctiva are continuous.
What are the components of the lacrimal apparatus?
- Lacrimal gland
- lacrimal cannaliculi
- lacrimal sac
- nasolacrimal duct
The lacrimal gland secretes lacrimal fluid, a watery, serous secretion into the conjunctival sac. What is the function of this fluid?
Lacrimal fluid keeps sclera and cornea moist and contains an antibacterial agent for protection.
What is the opening to the lacrimal cannaliculi?
Lacrimal punctum
Describe the flow of tears…
We should all be familliar with this by now due to medical school…
lacrimal gland –> conjunctival sac –> surface of eye –> lacrimal papillae with puncta –> cannaliculae –> lacrimal sac –> nasolacrimal duct
What causes corneal neovascularization?
Blood vessels grow into the corneal stroma secondary to hypoxia
What are the three tunics that the eyeball posesses?
- External fibrous tunic
- Middle vascular tunic
- Inner neural tunic
Should the cornea have vessels in it?
No
What provides most of the eye’s refractile capabilities?
Cornea
What is the function of the sclera?
- Structural support for the eye
- Muscle attachment
What are the components of the middle vascular tunic?
- Choroid
- Iris
- Ciliary body
The choroid contains melanocytes which produce melanind to absorb photons of light. What is the primary function of the choroid?
Provides vascular supply to the fibrous layer and outermost layers of retina.
The central aperture of the iris forms the pupil, and the iris controls the amount of light entering the pupil. By what muscles and innervations does this control occur?
- Sphincter pupillae
- Reduces diameter of pupil (miosis) to decrease light entering eye.
- Parasympathetic innervation (CN III).
- Dilator pupillae
- Increases diameter of pupil (mydriasis) to increase light entering eye.
- Sympathetic innervation.
The ciliary body has what components?
Ciliary processes
Ciliary muscle
What do the ciliary processes do?
Secrete aqueous humor into posterior chamber.
Attach to lens, enabling musculature to perform accomodation