Orbit and eyes Flashcards
Which bones form the orbital margins?
Supraorbital margin: frontal bone
Infraorbital margin: zygomatic bone (lateral) and maxilla (medial)
What is the special feature of the supraoribtal margin?
Supraorbital notch
Frontal nerves pass through here
Which bones form the roof of the orbit?
Frontal bone
Lesser wing of sphenoid
Which bones form the floor of the orbit?
Maxilla
Zygomatic bone
Palatine (small contribution)
Which bones form the lateral wall of the orbit?
Zygomatic bone
Greater wing of sphenoid
Which bones form the medial wall of the orbit?
Maxilla
Lacrimal bone
Ethmoid
Body of sphenoid
Where are fractures most likely to occur in the orbit?
Medial wall
Lateral wall
Which bones are most likely to fracture in the orbit? Why?
Lacrimal and ethmoid bones
Very thin and fragile
How many layers does the eye consist of?
What is the composition of each?
3
Outer layer: sclera and cornea; for stucture and protection
Middle layer: uvea, ciliary body, iris, choroid; vascular supply and nutrition
Inner layer: retina; vision
Describe the sclera?
Posterior 5/6 of eyeball
Tough
Made up of collagen
What is the function of the sclera?
Maintains shape of eyeball
Provides resistance against forces
Provides attachments for EOMs
Why is the sclera so tough?
Due to squiggly arrangement of collagen
Describe the cornea?
Anterior 1/6 of eye
5 layers (including epithelium, stroma and endothelium)
Avascular
Transparent
What is the function of the cornea?
Principal refracting component of eye
Why is the cornea transparent?
Due to the collagen being laid down in order; collagen fibrils of same diameter laid down in parallel, at equal distances
Why is the sclera opaque?
Collagenfibrils are different diameters, lengths, and lay at different angles to each other
In which layer of the cornea is the collagen found?
Stroma
What is the anterior chamber angle?
Junction between iris and cornea, where aqueous humour drains out of eye
What are the key structures in the anterior chamber angle?
Cornea
Trabecular meshwork
Canal of Sclemm
Ciliary body
Where does aqueous humour drain out of the eye?
In anterior chamber angle, via trabecular meshwork and Canal of Schlemm
What are the important structures in the ciliary body?
Ciliary processes (ciliary epithelium)
Ciliary muscle
What are the functions of the ciliary body?
Formation of aqueous humour (ciliary epithelium)
Tethers lens (ciliary processes)
Accommodation (ciliary muscle)
Where is aqueous humour produced?
Describe its pathway?
Formed in the ciliary epithelium of the ciliary processes
Then travels forward through pupil to drain via the trabecular meshwork of the anterior chamber angle
Which eye structures are involved in accommodation?
Ciliary muscle
Zonules that attach to lens
What is the function of the ciliary muscle?
Accommodation
Contracts and relaxes to change tension of zonules and therefore alter the shape of the lens
Describe the configuration of the ciliary muscle, zonules and lens for vieiwng both close and distant objects?
Close object: ciliary muscle contracted, zonules relaxed, lens bulgy
Distant object: ciliary muscle relaxed, zonules taught, lens thin
What is presbyopia?
Condition in which we lose our ability focus
Lens becomes inflexible
Occurs with age
What is the iris?
Aperture of the eye that forms the pupil
What are the two muscles that are associated with the iris?
What are their functions and innervation?
Sphincter pupillae: constricts pupil, parasympathetic innervation
Dilator pupillae: dilates pupil, sympathetic innervation
What is the choroid?
What is its function?
Three layers of blood vessels in eye
Supplies nutrients to retina
Where is the chorois located?
Between sclera and retina
What are the major structures associated with the retina?
Optic nerve/disc
Macula and fovea
What is the function of the macula and fovea?
Central vision
Describe the fovea?
Avascular
High density of cones
If the macula and fovea are avascular, where do they derive their nutrients from?
Choroid (beneath retina)
What is the optic nerve formed by?
Axons of ganlgion cells as they exit the retina
What is the lamina cribosa?
Band of dense connective tissue formed by 1/3 of the scleral fibres as they continue across where the optic nerve is
Sieve-hole that transmits nerve fibres
Where is the blood supply to they eye derived from?
Tributaries of the opthalmic artery, which is a branch of the internal carotid artery
What is the first branch of the opthalmic artery?
Central retinal artery
Pierces optic nerve to supply retina
What are the three ciliary arteries?
Long posterior
Short posterior
Anterior
What is the difference between long and short posterior ciliary arteries?
Short posterior arteries stop at the optic nerve
Long posterior arteries travel all the way around the retina
Where do posterior arteries pierce the eyeball?
Around the optic nerve
Where do anterior ciliary arteries pierce the eyeball?
They don’t
Travel around to front of eyeball
What are the vessels in the choroid fromed from?
Posterior ciliary artery
What do the anterior ciliary arteries supply?
Anterior eye structures
What do short posterior ciliary arteries supply?
Photoreceptors close to optic nerve and optic nerve head
What does the central retinal artery supply?
Inner retinal layer
What do the long posterior arteries supply?
Outer retina
Some anterior structures
Describe the blood supply to the retina?
Central retinal artery supplies the inner retina
Long posterior ciliary artery supplies the outer retina
Describe the eyelids?
Transition zone between skin and conjunctiva
Consist of glands, lashes, muscles and lacrimal apparatus
Which muscles are associated with the eyelid?
Describe their actions and innervation?
Orbicularis oculi: depresses upper lid, innervated by CN VII
Levator palpebrae superiosis: elevates upper lid, innervated by CN III
What is special about the actions of th eyelid muscles?
Never work together
If one is contracted, the other is relaxed
