The Orbit and Eye Flashcards
Eye-
Eye- eyeball and optic nerve
Orbit-
Orbit- eyeball and its accessory visual structures
Orbital region-
Orbital region- area of the face overlying the orbit and eyeball and includes the upper and lower eyelids and lacrimal apparatus
What are orbits?
- bilateral bony cavities in the facial skeleton that resemble hollow, quadrangular pyramids
Orbits
o Their bases directed __________
o Their apices directed _________
o The _____ walls are near parallel
o _______ walls are at right angles
o The axes of the orbits diverge at ____
anterolaterally
posteromedially
medial
Lateral
45°
Contents of the orbit and the anterior orbital region: (7)
o eyeballs
o accessory visual structures:
- Eyelids
- Extra-ocular muscles
- Nerves and vessels to eyeballs and muscles
- Orbital fascia surrounding eyeballs and muscles
- Mucous membrane (conjunctiva)
o Orbital fat- fills all space within orbits not occupied by the above structures
Boundaries of the orbit: (6)
- Base
- Superior wall
- Inferior wall (floor)
- Lateral wall
- Medial wall
- Apex
Boundaries of the orbit:
1. Base: (2)
- Outlined by the orbital margin
- Provides attachment for the orbital septum (fibrous membrane that extends into the eyelids)
Boundaries of the orbit:
2. Superior wall: (4)
- Formed by the orbital part of the frontal bone
- Separates the orbital cavity from the anterior cranial fossa
- Near the apex (posteriorly)- the superior wall is form by lesser wing of sphenoid
- Fossa for lacrimal gland- shallow depression anterolaterally in the frontal bone
Boundaries of the orbit:
3. Inferior wall (floor): (4)
- Mainly formed by maxilla and partly by zygomatic and palatine bones
- Slants inferiorly from the apex to the inferior orbital margin
- Demarcated from the lateral wall by inferior orbital fissure
- Inferior orbital fissure- gap between maxilla and sphenoid
Boundaries of the orbit:
4. Lateral wall: (3)
- Formed by the frontal process of the zygomatic bone and greater wing of sphenoid
- Strongest and thickest of the walls
- Posterior part separates it from the temporal and middle cranial fossae
Boundaries of the orbit:
5. Medial wall: (5)
- Formed primarily by the orbital plate of the ethmoid bone
- Frontal process of maxilla, lacrimal and sphenoid bones contribute
- Anteriorly- lacrimal groove and fossa for lacrimal sac
- Superiorly- trochlea for the tendon of a muscle
- Very thin
Boundaries of the orbit:
6. Apex:
- At the optic canal in the lesser wing of sphenoid just medial to the superior orbital fissure
Periorbita
* Lines the bones forming the orbit and is continuous with: (5)
o Dura mater at the optic canal and superior orbital fissure
o Pericranium over the orbital margins and through the inferior orbital fissure
o Orbital septa at the orbital margins
o Fascial sheaths of the extra-ocular muscles
o Orbital fascia that forms the fascial sheath of the eyeball
What are the eyelids?
Moveable folds that cover the eyeball anteriorly
What are the functions of the eyelids? (2)
o Protects the eye from injury and excessive light
o Keep the cornea moist by spreading lacrimal fluid
- Junctions of the ______ and _____ eyelids make up the medial and lateral palpebral commissures
- Covered externally by skin and internally by the ______ ________
- Palpebral conjunctiva is reflected onto the eyeball, where it is continuous with the _______ conjunctiva
superior and inferior
palpebral conjunctiva
bulbar
Bulbar conjunctiva: (3)
o Thin, transparent and loosely attached to the anterior surface of the eyeball
o Adherent to the periphery of the cornea
o Lines of reflection of the palpebral conjunctiva onto the eyeball are called the superior and
inferior conjunctival fornices
Conjunctival sac: (2)
o Space between the palpebral and bulbar conjunctivae
o Allows the eyelids to move freely over the surface of the eyeball
Superior and inferior tarsi: (3)
o Dense bands of connective tissue that strengthen the superior and inferior eyelids
o Palpebral part of orbicularis oculi is in the connective tissue superficial to the tarsi
o Tarsal glands embedded produce a lipid secretion that lubricates the edges of the eyelids to prevent them from sticking together when they close
Eyelashes: (2)
o In the margins of the eyelids
o Ciliary glands- large sebaceous glands associated with the eyelashes
Medial palpebral ligament: (3)
o Between the medial angle of the eye and the nose
o Connects the tarsi to the medial margin of the orbit
o Orbicularis oculi originates from and inserts onto this ligament
Lateral palpebral ligament:
o Attaches the tarsi to the lateral margin of the orbit
Orbital septum: (3)
o Fibrous membrane that spans from the tarsi to the margins of the orbit
o Becomes continuous with the periosteum
o Keeps the orbital fat contained
What does the lacrimal gland secrete?
Secrets lacrimal fluid
What is the function of lacrimal fluid? (3)
- Watery physiological saline containing the bactericidal enzyme lysozyme
- Moistens and lubricates the surfaces of the conjunctiva and cornea
- Provides nutrients and dissolved oxygen to the cornea
How is the Lacrimal gland divided?
o Divided into a superior orbital part and an inferior palpebral part by the lateral expansion of the
tendon of the levator palpebrae superioris
How is lacrimal fluid produced?
o Lacrimal fluid production is stimulated by parasympathetic impulses from facial nerve
- Excretory ducts of lacrimal gland:
o Convey lacrimal fluid from the lacrimal glands to the conjunctival sac
- Lacrimal canaliculi:
o Begin at lacrimal punctum on the lacrimal papilla near the medial angle of the eye and drain lacrimal fluid from the lacrimal lake to the lacrimal sac
- Nasolacrimal duct:
o Conveys lacrimal fluid to the inferior nasal meatus
Innervation of lacrimal gland:
Eyeball proper:
o Fibrous layer-
o Vascular layer-
o Inner layer of the eyeball-
o Fibrous layer- sclera and cornea
o Vascular layer- choroid, ciliary body and iris
o Inner layer of the eyeball- retina with optic and nonvisual parts
A connective tissue layer surrounds the eyeball. What does it consist of?
o Composed posteriorly by the fascial sheath of the eyeball (forming the actual socket of the
eyeball) and anteriorly by the bulbar conjunctiva
What is the episcleral space? (2)
- Potential space between the fascial sheath and the outer eyeball
- Allows for movement of the eyeball within the fascial sheath
What is the function of the fibrous layer?
o Provides shape and resistance
What is the sclera? (3)
- Tough opaque part of the fibrous layer covering the poster 5/6 of the eyeball
- Provides attachment for both extrinsic and intrinsic muscles of the eye
- Relatively avascular
What is the cornea? (4)
- Transparent part of the fibrous layer covering the anterior 1/6 of the eyeball
- Convexity of the cornea is greater than that of the sclera
- Appears to protrude from the eyeball when viewed laterally
- Completely avascular- relies on lacrimal fluid and aqueous humor for nourishment
How is the cornea innervated?
- Innervated by ophthalmic nerve- sensitive to touch
What is the choroid? (5)
- Dark, reddish-brown layer between the sclera and the retina
- Larger vessels are located externally on the scleral side
- Finer vessels are adjacent to the avascular retina
- Attaches firmly to the pigment layer of the retina
- Continuous anteriorly with ciliary body
What is the ciliary body? (5)
- Ring-like thickening of the vascular layer posterior to the corneoscleral junction
- Muscular and vascular
- Connects the choroid with the iris
- Provides attachment for lens
- Ciliary processes secrete aqueous humor- fills the anterior segment of the eyeball
What is the iris? (3)
- Lies on the anterior surface of the lens
- Thin contractile diaphragm with central aperture (pupil)
- 2 involuntary muscles control the size of the pupil
What are the 2 involuntary muscles control the size of the pupil?
- Sphincter pupillae- parasympathetically stimulated and circularly arranged (constrictor)
- Dilator pupillae- sympathetically stimulated and radially arranged (dilator)
What is the inner layer of the eye?
Optic part of retina
What is the optic part of the retina? (3)
- Has a pigmented layer and a neural layer
- Neural layer is light receptive
- Pigmented layer is a single layer of cells that reinforces the light-absorbing property of the
choroid in reducing the scattering of light in the eyeball
Ora serrata-
Ora serrata- irregular posterior border of the ciliary body where the optic part of the retina
terminates
Nonvisual retina: (2)
- Anterior continuation of the pigmented layer and a layer of supporting cells
- Extends over the ciliary body as the ciliary part of the retina and over the posterior surface
of the iris as the iridial part of the of the retina to the pupillary margin
What is the fundus of the eyeball? (2)
- Internal aspect of the posterior eyeball
where light entering the eyeball is focused - Has optic disc with no photoreceptors (blind
spot)- optic nerve and vessels conveyed
What is the Macula lutea?
- Small area just lateral to the optic disc
with special photoreceptor cones that is
specialized for acuity of vision.
What is the Fovea centralis?
Fovea centralis- depression at the
center of the macula where vision is
most acute
Compartments of the eyeball: (2)
Anterior segment
Posterior segment
Compartments of the eyeball:
o Anterior segment:
- Between cornea anteriorly and lens & ciliary
body posteriorly
How is the Anterior segment of the eye separated? (2)
- Subdivided into
- Anterior chamber- between cornea and iris/pupil
- Posterior chamber- between iris/pupil and lens & ciliary body
Compartments of the eyeball:
o Posterior segment:
- Posterior to the lens
- Refractive media of the eyeball: (3)
o Aqueous humor
o Lens
o Vitreous humor
What is aqueous humour? (4)
- Occupies the anterior segment of the eyeball
- Produces in the posterior chamber by the ciliary processes of the ciliary body
- Provides nutrients for the avascular cornea and lens
- Drains at the iridocorneal angle into the scleral venous sinus
What is the Lens? (2)
- Transparent, biconcave structure enclosed in a capsule
- Anchored by zonular fibers (collectively- suspensory ligaments)
What is the function of the ciliary muscle? (3)
- changes the shape of the lens when it contracts
- parasympathetic stimulation by oculomotor nerve causes contraction
- contraction results in the relaxation of the lens (lens thickens)
What is the Vitreous humor? (3)
- Watery fluid enclosed in the meshes of the vitreous body
- Vitreous body- transparent jelly-like substance posterior to the lens
- Holds the retina in place and supports the lens
Mechanism of constriction and dilation: (2)
Extraocular Muscles:
Levator palpebrae superioris
Main action:
Origin:
Insertion:
Innervation:
- Elevates superior eyelid
- Lesser wing of sphenoid anterosuperior to optic canal
- Superior tarsus of skin of superior eyelid
- Oculomotor n.
Extraocular Muscles:
Superior oblique
Main action:
Origin:
Insertion:
Innervation:
- Abducts, depresses and medially rotates eyeball
- Body of sphenoid
- Tendon passes through trochlea and inserts into sclera deep to sup. rectus
- Trochlear n.
Extraocular Muscles:
Inferior oblique
Main action:
Origin:
Insertion:
Innervation:
- Abducts, elevates and laterally rotates eyeball
- Anterior part of floor of orbit
- Sclera deep to lateral rectus
- Oculomotor n.
Extraocular Muscles:
Superior rectus
Main action:
Origin:
Insertion:
Innervation:
- Elevates, adducts and medially rotates eyeball
- Common tendinous ring
- Sclera just posterior to corneoscleral junction
- Oculomotor n.
Extraocular Muscles:
Inferior rectus
Main action:
Origin:
Insertion:
Innervation:
- Depresses, adducts and laterally rotates eyeball
- Common tendinous ring
- Sclera just posterior to corneoscleral junction
- Oculomotor n.
Extraocular Muscles:
Medial rectus
Main action:
Origin:
Insertion:
Innervation:
- Adducts eyeball
- Common tendinous ring
- Sclera just posterior to corneoscleral junction
- Oculomotor n.
Extraocular Muscles:
Lateral rectus
Main action:
Origin:
Insertion:
Innervation:
- Adducts eyeball
- Common tendinous ring
- Sclera just posterior to corneoscleral junction
- Abducent n.
Which extraocular muscles are used in general use?
What is the Optic nerve (CN II)?
- Enters from optic canal conveying purely sensory fibers
What is the Oculomotor (CN III)? (3)
- Divides into superior and inferior divisions
- Superior division supplies superior rectus and levator palpebrae superioris
- Inferior division
What is the inferior division of the Oculomotor (CN III)? (2)
o Supplies medial and inferior recti and inferior oblique muscles
o Carries presynaptic parasympathetic fibers to the ciliary ganglion
What is the Trochlear (CN IV)?
- Passes directly to superior oblique muscle
What is the Abducent (CN VI)?
- Passes directly to lateral rectus
What are the main branches of the Ophthalmic (CN V1)? (3)
- Frontal
- Nasociliary
- Lacrimal
What are the sub-branches of the frontal branch of the Ophthalmic (CN V1)? (2)
- Supratrochlear
- Supraorbital
What are the sub-branches of the Nasociliary branch of the Ophthalmic (CN V1)? (4)
What are the structures innervated by Supratrochlear of the Ophthalmic nerve? (3)
- Conjunctiva of upper eyelid
- Skin of upper eyelid
- Forehead and anterior scalp
What are the structures innervated by Supraorbital of the Ophthalmic nerve?
Forehead and anterior scalp
What are the structures innervated by the Posterior ethmoidal of the Ophthalmic nerve? (2)
- Mucosa of ethmoidal and sphenoidal sinuses
- Mucosa of nasal cavity
What are the structures innervated by Anterior ethmoidal of the Ophthalmic nerve? (2)
- Skin of the dorsum of the nose (external nasal)
- Dura mater (from meningeal branch)
What are the structures innervated by Long ciliary branch of the Ophthalmic nerve? (2)
- Ciliary body, iris and cornea
- Dilator pupillae (sympathetic fibers)
What are the structures innervated by the Lacrimal branch of the Ophthalmic nerve?
- Lacrimal gland
- Conjunctiva and skin covering the lateral part of the upper eyelid
Ciliary ganglion: (2)
- Group of postsynaptic parasympathetic nerve cell bodies
- Located between the optic nerve and lateral rectus posteriorly
The ciliary ganglion receives nerve fibres from 3 sources:
Ciliary ganglion:
* Short ciliary fibers arise here….
o Supply sympathetic and parasympathetic fibers to ciliary body and iris
Arteries of orbit: (3)
- Ophthalmic
- Ophthalmic and maxillary
- Maxillary (3rd part)
What are the branches of the ophthalmic artery?
Ophthalmic artery
Branch: Central retinal
Distribution:
Supplies optic retina
Ophthalmic artery
Branch: Supraorbital
Distribution:
Forehead and scalp
Ophthalmic artery
Branch: Supratrochlear
Distribution:
Forehead and scalp
Ophthalmic artery
Branch: Lacrimal
Distribution:
Lacrimal gland, conjunctiva and eyelids
Ophthalmic artery
Branch: Dorsal nasal
Distribution:
Dorsal aspect of nose
Ophthalmic artery
Branch: Short posterior ciliaries
Distribution:
Cones and rods of optic retina
Ophthalmic artery
Branch: Long posterior ciliaries
Distribution:
Ciliary body and iris
Ophthalmic artery
Branch: Posterior ethmoidal
Distribution:
Posterior ethmoidal cells
Ophthalmic artery
Branch: Anterior ethmoidal
Distribution: (4)
Anterior and middle
ethmoidal cells
Frontal sinus
Nasal cavity
Skin on dorsum of nose
Ophthalmic and maxillary
Branch: Anterior ciliary
Distribution:
Iris and ciliary body
Maxillary (3rd part)
Branch: Infraorbital
Distribution: (2)
Inferior oblique and rectus muscles
Lacrimal sac
