Eye and Orbit Week 2 FINISHED Flashcards
What is the shape of the orbit?
Pyramidal (base anteriorly, 4 walls, apex posteriorly)
What does the orbit contain?
Eyeball and muscles
Nerves
Blood vessels
Most of the lacrimal apparatus
What is the function of the orbit?
To protect its structures (eyeball and muscles, etc)
What are the 4 walls of the orbit?
Medial, lateral, inferior, superior
What is the orbit lined with? What is it continued with?
Periosteum, called the periorbita. It is continuous with the dura of the optic canal and the superior orbital fissure. Also continuous over the orbital margins with the periosteum of the skull
What is the orientation of the superior wall of the orbit?
Horizontal
What forms the superior wall of the orbit?
The majority is formed by the orbital region of the frontal bone. Posteriorly, near the apex, it is formed by the lesser wing of the sphenoid.
What fossa does the superior wall of the orbit contain?
The fossa for the lacrimal gland, called the lacrimal fossa
What forms the medial wall of the orbit?
Primarily the ethmoid bone. Also by the frontal, lacrimal and sphenoid bones
What is found in the anterior part of the medial wall of the orbit?
The lacrimal fossa for the lacrimal sac, and the proximal part of the nasolacrimal duct
What is the medial wall of the orbit parallel with?
The medial wall of the orbit of the other eye
What are the 2 medial walls of the orbits divided/separated by?
The ethmoid sinuses and upper nasal cavity
What forms the inferior wall of the orbit?
Mostly by the maxilla. Partly by the zygomatic and palatine bones
What is the lateral wall of the orbit formed by?
By the zygomatic bone (frontal process) and the greater wing of the sphenoid
Are the 2 lateral walls of the orbit perpendicular?
Almost
What is in the apex of the orbit?
The optic canal
What bone is the apex of the orbit in?
The lesser wing of the sphenoid just medial to the superior orbital fissure
What is the function of the eyelids?
To protect the cornea from dust, excessive light etc
To cover the anterior eyeball when closed
To help keep the cornea moist by spreading lacrimal fluid
What is on the external surface of the eyelids?
Skin
What is on the internal surface of the eyelids?
Palpebral conjunctiva
What is the conjunctiva?
Mucous membrane lining the inner surface of the eyelid and anterior eyeball
What is the palpebral conjunctiva?
The conjunctiva which lines the eyelids
What is the bulbar conjunctiva?
The conjunctiva which lines the anterior eyeball (sclera)
What are the conjunctival fornices? How many are there and what are they called?
Where the bulbar and palpebral conjunctiva meet. There are 2, the superior and inferior fornices
What are the tarsal plates? How many are there per eye?
The eyelids are strengthened by dense bands of connective tissue. 2 per eye
What is also known as the skeleton of the eye?
The tarsal plate of the eyelids
Where are the tarsal glands located?
Within the tarsal plates
What do tarsal glands do?
Secrete lipid substances
Lubricates the edges of the eyelids and prevents them sticking together
Acts as a barrier so that lacrimal fluid doesn’t cross the eyelid (except excessive fluid - tears)
Where is the orbicular oculi found in relation to the skin and tarsal plates of the eyelids.
Deep to the skin, superficial to the tarsal plates
What are the medial and lateral angles (where the upper and lower eyelids meet) called?
Canthi
What are the 2 main ligaments of the eyelids?
The medial and lateral palpebral ligaments
What does the lateral palpebral ligament connect the tarsal plates to? Does it have any muscular attachments?
It connects the tarsal plates to the lateral margin of the orbit.
It has no muscular attachments
Where does the medial palpebral ligament attach? Does it have any muscular attachments?
It attaches between the medial angle of the eye/medial canthi and the nose. It also connects the tarsal plates to the medial margin of the orbit.
It attaches to the orbicularis occuli muscle
What are the glands at bases of the eyelashes called? What type of gland are they?
They are called the ciliary glands. They are sebaceous glands.
What does the lacrimal apparatus consist of?
Lacrimal glands Lacrimal ducts Lacrimal lake Lacrimal canaliculi Lacrimal sac Nasolacrimal duct Lacrimal fluid
What is the size and shape of the lacrimal glands?
Almond shaped, 2cm long
Where are the lacrimal glands found?
In the lacrimal fossa which is located in the frontal bone in the superior lateral aspect of the orbit.
What is the function of the lacrimal gland?
To secrete lacrimal fluid
Where are the accessory lacrimal glands most numerous?
In the upper eyelids
How many lacrimal ducts are there per eye?
Up to 12
What is the function of the lacrimal ducts? Where do they open?
They convey fluid from the lacrimal glands to the conjunctival sac (space bound by the conjunctival membrane between the palpebral and bulbar conjunctiva)
They open into the superior conjunctival fornix
What is the lacrimal lake and where is it found?
The triangular space that is in the medial angle of the eye where tears collect
What are the lacrimal canailculi? Where do they commence?
Small canals that drain lacrimal fluid from the lacrimal lake into the nasolacrimal duct. They commence on the lacrimal punctum (point) on the lacrimal papilla near the medial angle of the eye.
What is the lacrimal sac?
The dilated superior portion of the nasolacrimal duct
What is the function of the nasolacrimal duct?
To drain lacrimal fluid from the lacrimal lake into the nasal cavity
What usually happens to the lacrimal fluid?
It is swallowed unless there is an excess in which case it flows over the lipid barrier of the edge of the lower eyelids and onto the cheeks
In which direction does lacrimal fluid flow? Why?
Lateral to medial. Mostly because the eyes close in a lateral to medial direction
What stimulates the production of lacrimal fluid?
PSNS impulses from CNVII (Cn 7, facial nerve)
SNS impulses from the superior cervical ganglion
What are the orbital contents?
Eyeball Optic nerve Ocular muscle Fascia Nerves Vessels Fat Lacrimal gland and sac
How many layers does the eyeball have? What are they?
3 layers
Outer fibrous layer (sclera and cornea)
Middle vascular layer (choroid, ciliary body, iris)
Inner layer (retina, optic and non visual parts)
What is the sclera? How much of the eyeball does it cover?
It is the opaque part of the fibrous coat of the eyeball, often referred to as the white of the eye.
It covers the posterior 5/6 of the eyeball.
What is the cornea? How much of the eyeball does it cover?
It is the transparent part of the fibrous coat of the eyeball.
It covers 1/6 of the anterior part of the eyeball
Is the cornea vascular or avascular? What is it sensitive to?
It is avascular and sensitive to touch
What nerves supplies the cornea?
The ophthalmic nerve
How is the cornea nourished?
It is nourished by the aqueous humour, tears and absorbs oxygen from the air
What is the choroid? Where does it terminate?
A dark brown membrane between the sclera and the retina. It terminates anteriorly in the ciliary bodies.
What does the choroid contain?
Blood vessels and pigments which absorb excess light
What 2 parts does the ciliary body have?
A muscular part and a vascular part
What is the function of the ciliary body?
It connects the choroid with the circumference of the iris.
It also secretes aqueous humour which fills the anterior and posterior chambers of the eye
What are the folds on the internal surface of the ciliary body called?
Ciliary processes
What are the chambers of the eye called, where are they located and what do they contain?
Anterior chamber: between the cornea anteriorly and the pupil and iris posteriorly
Posterior chamber: Between the pupil and iris anteriorly, and the ciliary body posteriorly
What is the iris and where is it located?
It is a thin contractive muscular diaphragm. It lies anterior to the lens.
What is the pupil and what is its size controlled by?
It is the central aperture of the iris and its size controlled by 2 muscles of the iris:
Sphincter pupillae (closes) Dilator pupillae (opens)
What is the retina and what is it continuous with?
It is a delicate 10 layered nervous tissue membrane that receives visual images of external objects and transmits impulses via the optic nerves (with which it is continuous) to the brain.
What are the outer and inner layers of the retina in contact with?
The outer layer is in contact with the choroid.
The inner layer is in contact with the vitreous body
What is found posterior in the retina? What is this region insensitive to?
A circular depressed region called the optic disc in which the optic nerve enters the eye. This region is insensitive to light.
What are the 2 types of photos receptors?
Rod cells
Cone cells
What are rod cells? How many are there per eye and where are they located in the eye? What is their function?
They are photoreceptors.
There are over 100 million per eye.
They are positioned on the peripheral parts of the retina and respond to dim light for black and white vision, they also respond to form and movement but have poor visual acuity.
What are cone cells? How many are there per eye? What is their function and where are they located?
They are photo receptors.
There are about 7 million per eye.
They provide daylight and colour vision and greater visual acuity. They are concentrated in the fovea.
What are the refractive media of the eye? What do they do?
Cornea, aqueous humour, lens and vitreous body.
These are parts of the eye which cause the refraction of light / change in the direction of light.
What is aqueous humour? What produces it? Where is it found?
It is found in the anterior and posterior chambers of the eye.
Produced by the ciliary processes.
It is a clear watery solution that provides nutrients for the avascular cornea and lens.
Where does the aqueous humour drain?
Drains into the iridocorneal angle into the scleral venous sinus.
What is the lens of the eye? Where is it located?
It is a transparent biconvex structure enclosed within a capsule.
It is posterior to the iris.
What anchors the capsule of the lens to the ciliary body?
The suspensory ligaments
What is the capsule of the lens anchored to?
The Ciliary body
What does changing the convexity of the lens do? How is the changing of the convexity changed?
It changes whether your eyes are focussing near or far away.
It is achieved by the ciliary muscles of the ciliary body.
What does increasing the convexity of the lens allow for?
Near vision
What does flattening the lens allow for?
Long distance vision.
What is vitreous humour? Where is it found? How much of the eyeball does it fill?
A jelly like substance. It is found posterior to the lens and fills the posterior 4/5ths of the eyeball.
How many muscles of the orbit are there? What are they?
7
Levator Palpebrae Superioris
4 Recti muscles
2 Oblique muscles
What does recti mean?
Straight
Why are rectus muscles called ‘rectus’?
Because they are relatively straight
What is levator palpebrae superioris? What does it do?
Thin, flat muscles which elevates the upper eyelid.
Levator palpebrae superioris OIAN
O: Lesser wing of the sphenoid (anterior and superior to the optic canal)
I: Tarsal plate and skin of the upper eyelid
A: Elevates the upper eyelid
N: Oculomotor nerve (CN III) as well as some SNS innervation for flight fright reaction
Origin and insertion of the superior, inferior, medial and lateral rectus muscle
Origin:
- Common tendinous ring: a fibrous cuff at the back of the eyeball. Surrounds the optic canal and the medial part of the superior orbital fissure
Inserts:
Sclera just posterior to the cornea.
What is the action of the superior rectus? What is its nerve supply? What axis does it run along?
Elevates, adducts and medially rotates the eye.
CN III
Runs along the axis of the orbit.
What is the action of the inferior rectus muscle? What is its nerve supply?
Depresses, adducts and laterally rotates the eye.
CN III
Why do the inferior and superior rectus muscles have an adduction effect?
It is not parallel to the long axis of the eyeball hence the adduction
What is the action of the medial rectus? What is its nerve supply?
It adducts the eyeball.
CN III
What is the action of the lateral rectus? What is its nerve supply?
Its abducts the eyeball
CN VI
Superior oblique OIAN
Origin - Body of the sphenoid
Inserts - Sclera, deep to superior rectus mm
Its tendon passes through a fibrous ring (trochlea) lined with a synovial sheath allows easy slide, causes it to change direction
Action - Abducts, depresses and medially rotates the eyeball
Nerve supply - Trochlea nerve CN IV
Inferior Oblique OIAN
Origin - Anterior part of the floor of the orbit
Inserts - Sclera deep to the lateral rectus mm
Action - Abducts, elevates and laterally rotates the eye
Nerve supply - Oculomotor nerve CN III
What is the innervation of the orbit?
The optic nerve runs into the posterior aspect of the eyeball.
Other nerves supply the orbit
- Oculomotor (CN III)
- Trochlear (CN VI)
- Abducens (CN VI)
- Branches from the ophthalmic nerve (CN V (1))
What is the arterial supply to the eyeball?
Mainly from the ophthalmic artery (a branch of the internal carotid artery)
Also partially from the infraorbital artery, a branch of the maxillary artery (a branch of the external carotid artery)
What is the venous supply to the eyeball?
Inferior and superior Ophthalmic veins
Pass through the SOF - drain into the Cavernous sinus
Central vein of the retina, usually drains directly into cavernous sinus, may join one of the Ophthalmic veins
Where is the aqueous fluid reabsorbed?
The canal of schlemm (corneal ciliary junction)
Where do we have the greatest acuity for vision?
The fovea pit
What are the 3 intraocular muscles?
CIliary muscles
Sphincter pupillae
Dilator pupillae
Where do the rectus muscles attach to the eyeball?
The sclera of the eyeball
Where does the axis of the orbit run? Is it the same as the axis of the eyeball?
The axis of the orbit runs through the apex of the orbit, in the lesser wing of the sphenoid. It is not the same as the axis of the eyeball which are parallel to each other.
What is the trochlear spine? What does it do?
A little bony projection that comes off the frontal bone. Attached to it is a trochlear ring made of fibrocartilaginous tissue through which the superior oblique muscles runs.
