week 2, eye and orbit Flashcards
What is the Orbit?
A bony cavity in the facial skeleton
What is the orientation of the orbit?
it is pyramidal containing;
A base
4 walls
Apex posteriorly
What does the orbit contain?
Eyeball Optic nerve Ocular muscles Fascia Nerves Vessels Fat Lacrimal gland and sac
What is the function of the orbit?
Protection of the structures held within it. Serves as a vessel for the eyeball
How many walls are there of the orbit and what are they?
4 walls, Superior Inferior Medial Lateral
What is the orbit lined with?
Periosteum called periorbita
What is periorbita continuous with?
the dura at the optic canal and the superior orbital fissure
What is the superior wall of the orbit formed by? What does the superior wall contain?
The Frontal bone
The posterior aspect if formed by the greater wing of the sphenoid
It contains the fossa for the lacrimal gland
What is the medial wall of the orbit formed by?
Mostly by the ethmoid bone
Frontal bone
Lacrimal bone
Sphenoid bone
What is found anterior to the medial wall of the orbit?
The lacrimal fossa
the lacrimal sac
Proximal part of the nasolacrimal duct
What separates the medial walls of the orbit?
The ethmoid sinuses and upper nasal cavity
What is the inferior wall of the orbit formed by?
Mainly by the maxilla
Partly by the zygomatic and palatine bones
What is the lateral wall of the orbit formed by?
Formed by the zygomatic bone and the greater wing of the sphenoid
What is the orientation of both lateral walls of the orbit?
The two lateral walls are almost perpendicular (occur at right angles to each other)
Where is the apex of the orbit found?
It is found at the optic canal in the lesser wing of the sphenoid just medial to the superior orbital foramen
What is the function of the eyelid?
Protects the cornea from dust and excessive light
Covers the anterior eyeball when closed
Helps keep cornea moist by spreading lacrimal fluid
What is found externally and internally to the eyelid?
Externally = Skin Internally = palpebral conjunctiva
What is the conjunctiva?
Mucous membrane that lines the inner surface of the eyelid and anterior eyeball
What is the palpebral conjunctiva?
Mucous membrane that lines the eyelid
What is the bulbar conjunctiva?
Mucous membrane that lines the anterior eyeball (sclera)
What are the conjunctiva fornices?
The place at which the palpebral and bulbar conjunctiva meet. (both superior and inferior)
What are the tarsal plates?
Dense bands of connective tissue that form the “skeleton” of the superior and inferior eyelids
What are the tarsal glands?
glands that secrete lipid substance which lubricates the edges of the eyelids, preventing them from sticking together.
Found within tarsal plates
What are the ligaments of the eyelid?
Lateral and Medial palpebral ligaments
These connect the tarsal plates to the orbit and nose
What is the orbicularis occuli muscle?
The circular muscle surrounding the tarsal plates
What does the lacrimal apparatus consist of?
Lacrimal glands Lacrimal ducts Lacrimal lake Lacrimal canaliculi Lacrimal sac Nasolacrimal duct
What causes the release of lacrimal fluid?
The facial nerve
What are the three layers of the eyeball?
Outer fiborous layer (sclera,cornea)
Middle vascular layer (choroid, ciliary body, iris)
Inner layer (retina, optic and non visual parts)
What is the cornea?
The transperant part of the fiborous coat which covers the anterior 1/6 of the eyeball
it is avascular and sensitive to touch
What is the choroid and where is it found?
A drak brown membrane found in the middle vascular layer between the sclera and retina
It absorbs excess light
What is the cillary body? What is its function?
It connects the choroid with the circumference of the iris
Secretes aqueous humor which fills the anterior and posterior chambers of the eye
How many chambers of the eye are there and what are they?
two;
Anterior (between cornea and iris anteriorly and the iris and pupil posteriorly)
Posterior (Between iris and pupil anteriorly and the lens and the ciliary body posteriorly)
What is the iris and where is it found?
A thin contractile muscular diaphragm that lies anterior to the lens, it is responsible for dilating and contracting the pupil)
What is the retina?
a 10 layered nervous tissue membrane which is continuous to the optic nerve
it recieves visual images of external objects and transmits impulses via the optic nerve to the brain
What are rod cells and where are they found?
They are photoreceptors located peripherally in the retina. they respond to dim light for black and white vision
What are cone cells and where are they found?
They are photoreceptors that provide daylight colour vision and greater visual acuity
They are concentrated in the fovea
What are the muscles of the orbit?
There are 7:
Levator Palpebrae Superioris
Superior, inferior, medial and lateral rectus muscles
Superior and inferior oblique muscles
What is the nerve supply to all the eye muscles apart from one. Which muscle is the other one and what supplies it?
Oculomotor nerve for all muscles
Apart from lateral rectus which is supplies by the abducent nerve
What nerves innervate the orbit?
Occulomotor
Trochlea
Abducent
Branches of the opthalmic nerve
What areries supply the orbit?
Opthalmic artery (branch of the internal carotid artery)
infraorbital artery (branch of the maxillary artery)
What do the veins of the orbit pass through and drain into?
Pass through the superior orbital foramen and drain into the cavernous sinus
