What muscles make up the iris of the eye?
Constrictor and radial muscles
Name some functions of the ciliary body?
Suspends Lens
Produces Aqueous humour
What is the function of the choroid?
Supplies blood to the outer layers of retina
What are the three layers of the eyeball?
Fibrous Coat
Vascular Coat
Sensory Body
What makes up the fibrous coat?
Cornea and Sclera
What makes up the vascular coat (uvea)?
Iris, Ciliary Body, Choroid
What makes up the sensory body?
Retina (10 layers - made up of rods and cones)
Where is the aqueous humour located?
Anterior segment (in front of Lens)
What is the function of the aqueous humour?
Helps maintain intraocular pressure.
It is constantly produced and reabsorbed.
How is the anterior segment divided?
Anterior Chamber (In front of iris)
Posterior Chamber (behind iris
Where does the aqueous humour travel to?
Produced from the ciliary body -> Posterior chamber -> Anterior chamber -> Angle of anterior chamber
Where does the aqueous humour drain out?
The trabecular meshwork at the angle of the anterior chamber.
Then into Schlem’s canal -> Episcleral veins
Where is the vitreous humour located?
Posterior Segment (Behind the lens)
What is the function of the vitreous humour?
Cushions the retina. (Retinal detachment occurs when becomes more liquefied)
What is the shape of the lens?
Biconvex (suspended in 360 degree by suspensory ligaments of ciliary muscle)
What are the three openings of the bony orbit?
Optic foramen, Superior orbital fissure, Inferior orbital fissure
What is the space in the orbit filled with?
Fat (to support the eyeball) - one of the last reserves of fat in starvation.
What happens to the eyes in hyperthyroidism?
Hypertrophy of the orbit - causing a protruding appearance
How does sty formation happen?
Eyelash sebaceous glands being blocked?
What muscle helps to open the eyelid?
Levator Palpabra Superioris (LPS)
What muscle helps to close the eyelid?
Orbicularis Oculi
What is the function of the tarsal plate in the eyelid?
Helps to prevent the eyelid to scrunch up
Where is the lacrimal gland located?
In the roof of the orbit
What nerve provides function to the lacrimal gland?
The facial nerve (parasympathetic)
What does the lacrimal fluid drain into?
The lacrimal sac via punctae on the medial side of the eyelid - into nasolacrimal duct.
What does the nasolacrimal duct drain into?
The inferior nasal cavity
What happens with blinking?
The orbicularis oculi pulls the lacrimal sac open - negative pressure pulls in tears.
What are the intrinsic ocular muscles?
Ciliaris muscle, constrictor pupillae, dilator pupillae
What is the function of the ciliaris muscle?
When it contracts, makes lens change shape - accommodation
What cranial nerve controls the ciliaris muscle?
Oculomotor Nerve (CNIII)
What is the function of the constrictor pupillae?
Pupillary constriction
What cranial nerve controls the constrictor pupillae muscle?
Oculomotor Nerve (CNIII)
What is the function of the dilator pupillae?
Pupillary dilatation
What nerves controls the dilatator pupillae muscle?
Sympathetic nerves
What are the extrinsic muscles of the eye?
Superior Rectus Inferior Rectus Medial Rectus Lateral Rectus Superior Oblique Inferior Oblique
What extrinsic muscles are innervated by the occulomotor nerve CNIII?
Superior Rectus Inferior Rectus Medial Rectus Inferior Oblique (LPS)
What extrinsic muscles are innervated by the trochlear nerve CNIV?
Superior Oblique
What extrinsic muscles are innervated by the abducens nerve CNVI?
Lateral Rectus
Which of the ocular cranial nerves is most frequently damaged?
Abducens Nerve (CNVI)
Where does the trochlear nerve CNIV arise from?
The back of the brainstem
Where do the cranial nerves III, IV and VI enter the orbit?
Superior orbital fissure
Where does the general sensory innervation to the eyeball arise from?
CNV1 (from trigeminal, and CNV2)
What are the branches of the opthalmic nerve? (CNV1)
Nasociliary, Frontal, Lacrimal
Where does the maxillary nerve (CNV2) enter the orbit?
Inferior orbital fissure
What blood vessel supplies blood to the eye/orbit?
Opthalmic artery (branch of internal carotid artery)
What artery supplies the inner layers of retina?
Central Retinal Artery
Where is the physiological blindspot?
The optic disc
What does the central retinal vein look like compared to the artery
The vein is wider and darker
Which venous sinus does the opthalmic veins drain in to?
Cavernous sinus
Where does the cavernous sinus drain into?
The internal jugular veins (exit through the jugular foramen)
What does the cavernous sins lie to either side of?
The body of the sphenoid bone.
In embryology, what induces ectodermal cells to enlarge and form the nueral plate?
The notochord
What does the neural plate fold up to become?
The neural tube
What part of the neural tube gives rise to optic vesicles?
Diencephalon
How is the lens placode formed?
Optic vesicles induce surface epithelium to thicken
What does the optic vesicle form?
Optic cup
What forms the choroid, sclera and extraocular muscle in the developing embryo?
Surrounding mesenchyme
What form the lens?
Lens vesicle
What forms the cornea, conjunctiva, eyelids?
Surface epithelium
Between which layers of retina can a potential space form?
9-10
What is refraction?
The bending of light from one optical medium to another
What make up the refractive media in the eyeball?
Cornea, Aqueous Humour, Lens
What happens to the lens as an object becomes closer?
The lens becomes thicker
To form a clear image on the retina
Which of the refractive media is the most powerful?
The cornea
What is the term used to describe the changes in both eyes as it changes focus from a distant object to a close object?
Accommodation
What three things comprise accommodation?
Lens changes shape (ciliary body contraction)
Pupil constricts
Eyes converge
What controls all three aspects of accomodation?
Parasympathetic innervation from CNIII (Oculomotor Nerve)
What term describes a refractory error causing short-sightedness?
Myopia
What term describes a refractory error causing long-sightedness?
Hyperopia
What term describes a refractory error causing non-spherical curvature of the cornea?
Astigmatism
What term describes a refractory error causing long-sightedness in old age?
Presbyopia
What is phototransduction?
Light waves stimulating photoreceptor cells in the retina
What is the visual pigment in rods and cones?
Rhodopsin (Opsin + Retinal)
What vitamin forms the chromophore in opsin?
Vitamin A
What happens when rhodopsin splits?
Bleaching
What role does vitamin A from the liver play in the visual pigment?
Visual pigment regeneration
What can happen to the eyes in response to raised ICP?
Increased pressure around optic nerves
What is the descriptive term for everything seen with one eye?
Visual field
Where is the area of peak central vision?
Fovea centralis
What happens to objects in the visual field?
Formed upside down and inverted on the retina
Where to fibres from the optic nerve pass to?
The optic chiasm
What happens at the optic chiasm?
Medial nasal fibres cross to the opposite side
What fibres does each optic tract contain?
Fibres from the (lateral) temporal half of the ipsilateral eye and the crossed-over nasal fibres from the contralateral eye.
Where do the optic tract fibres synapse?
The Lateral Geniculate Body (LGB) of the thalamus
Where is the Primary Visual Cortex located?
Occipital Lobe
What visual disruption occurs when the right optic nerve is damaged?
Blindness in R Eye
What visual disruption occurs when the optic chiasm is damaged?
Bitemporal Hemianopia
What visual disruption occurs when the right optic tract is damaged?
Contralateral Homonymous Haemianopia
What visual disruption occurs when the right optic radiation is damaged?
Contralateral Homonymous Haemianopia
What is the function of intrinsic eye muscles?
Control pupil diameter & helps alter lens curvature to enable us to see near objects
What is the function of extrinsic eye muscles?
Move the eye
What is the action of the Lateral Rectus?
Abduction
What is the action of the Medial Rectus?
Adduction
What is the action of the Superior Rectus?
Elevation
Adduction
Intorsion
What is the action of the Inferior Rectus?
Depression
Adduction
Extorsion
What is the action of the Superior Oblique?
Intorsion
Depression
Abduction
What is the action of the Inferior Oblique?
Extorsion
Elevation
Abduction
What does the terminology RADSIN refer to?
Recti ADductors,
Superiors INtortors
What terminology means misalignment of eyes?
Strabismus (Squint)
What are the functional consequences of squint?
- Amblyopia (lazy eye)
- Diplopia (double vision)
What does increased illumination do to pupils?
Constriction (through parasympathetic innervation)
What does decreased illumination do to pupils?
Dilation (through sympathetic innervation)
Where does the afferent limb of the light reflex travel to?
The midbrain (where the IIIn nucleus is located)
Does conjunctiva cover the cornea?
No
What is the epithelium of the cornea?
Stratified squamous non-keratinised
What is the bowman’s membrane?
Basement membrane of corneal epithelium
What is the regularly arranged layer of collagen known as beneath bowman’s membrane?
Stroma
Why is the avascularity of the cornea beneficial for graft surgery?
Lesser chance of foreign antigens from a corneal graft being recognised by the recipient -> lesser chance of a graft rejection.
What are consequences of raised IOP?
Pressure on nerve fibres on surface of retina -> die out -> visual field defects
Altered field of vision