Eye Flashcards
What are the 5 histological layers of the cornea?
1=stratified squamous non-keratinsed epithelium
2=Bowman’s membrane
3=Stroma (regulary arranged collagen)
4=Descemet’s layer
5=endothelium
What function does the endothelium of the cornea have?
Has a pump that actively keeps out aqueous humor
What is the pathway of aqueous humor
the ciliary body releases aqueous humor into the anterior chamber, at the angle of the anterior chamber is drains through the trabecular meshwork, it then reaches a little tube known as the schlemm’s canal
Why is the fovea centralis have max visual acuity?
packed with cones
Describe the lens of the eye
A transparent, crystalline biconvex structure which is suspended by zonules from the ciliary body
What is lens opacification called?
cataract
Function of tear film
Cornea moist, wash away particulate foreign bodies, contains antibodies and lysozymes, smooths outer surface of cornea- so smooth surface for refraction
the 3 layers of the tear film?
layer 1= mucinous layer overlying corneal epithelium
layer 2= aqueous layer
layer 3= oily layer
What nerve stimulates secretion of tears into conjunctival sac?
parasympathetic- facial nerve
What distributes a tear film across the eye?
when you blink the sharp lower border of the upper eyelid distributes tear film evenly
What stimulates you to blink?
when your eyelids are open, the aqueous component of tears begin to evaporate, and the oily layer becomes to close to the mucin layer.
When these 2 layers touch the tear film breaks up and your eyelid is stimulated to blink
What is refraction?
bending of light when it passes from one optical medium to another
What is refraction in relation to the eye?
light waves from an object bend at the cornea, they are bent some more at the lens to form a clear image on the retina.
What is accommodation
The change that occurs in eyes when it changes focus from a distant (infinity) to a close object (20cm)
When does a lens thicken and what does this help the eye do?
A lens thickens during accomodation to help focus on closer objects
Describe the steps of a lens thickening
Ciliary muscles contracts making the ciliary body bulge, space in the middle decreases, suspensory ligaments become lax, lens is no longer under stretch and lens becomes thicker
What is the 2nd step on accommodation
pupil constriction via pupillary constrictor muscle around the border of the pupil, via parasympathetic (CNIII) innervation
What is the 3rd step of accommodation
eyes convergence- when you focus on a close object out eyes have to both turn in medially using the medial recti muscles
What is the name for perfect vision?
emmetrope
What is myopia?
shortsightedness
distant objects look hazy
What is phototransduction?
conversion of light energy to an electrochemical response by the photoreceptors (rods and cones)
What is the visual pigment in rods?
in the lamellae cell membrane of the rod is a visual pigment called rhodopsin
What is the visual pigment in cones?
in the lamellae cell membrane of cones is visual pigment called opsins S, M and L
What happens when light hits the visual pigment?
11-cis retinal sits in the opsins (made from dietary vit-A), when light falls on 11-cis retinal, it isomerises into all-trans retinal
all trans retinal cannot fit in the opsin, so rhodopsin spilts resulting in bleeching
What does bleaching of visual pigment cause?
Causes a phototransdution cascade, this is a cascade of reactions causing hyperpolarisation, transmitting an impulse, which becomes an action potential in the optic cells
What role does vitamin A play in visual pigment?
visual pigment regeneration
signs of vitamin A deficiency in the eye
Bitot’s spot on conjunctiva, corneal ulceration, corneal melting
How can your visual field be tested?
by confrontation test or automated perimetry
Where do fibres from the optic tract synapse?
fibres from the optic tract synapse at the Lateral geniculate body of the thalamus
Describe the steps of a visual pathway
All fibres from the eye pass through the optic nerve to the optic chiasma,
the nasal fibres cross to the opposite side, thus the optic tract contains fibres from the temporal half of the ipsilateral eye and the corssed-over nasal fibres from the contralateral eye .
fibres from the optic tract synapse at the LGB of the thalamus.
optic radiation passes behind the internal capsule to reach the primary visual cortex in the occipital lobe
What causes contralateral homonymous hemianopia?
right optic tract damage, optic radiation damage
What causes bitemporal hemianopia
optic chiasma disrupted in the middle
Role of intrinsic muscles?
control pupil diameter and help alter lens curvature to enable us to see near objects
Role of extrinsic muscles?
move the eye
What do the recti muscles arise from?
they arise from the apex of the orbit from an annular fibrous ring
Where does the superior oblique muscle arise from
from the roof of the orbit posteriorly
Where does the inferior oblique muscle arise from
the floor of the orbit anteriorly
what does LPS stand for and what does this muscle do?
levator palpebrae superioris
this muscle elevates the eyelids
What does strabismus mean
squint
Types of squint?
Esotropia- manifest convergent squint, one eye is deviated inward
Exotropia- manifest divergent squint, one or both eyes look outward
Functional consequences of squint?
Amblyopia, diplopia
What is amblyopia?
lazy eye
brain supresses the image of 1 eye leading to poor vision in that eye without pathology
What is diplopia?
double vision
usually occurs in squints as a result of nerve palsies
Where do fibres destined to activate pupillary reflex go to
Rather than go to LGB, they leave the optic tract and go to the midbrain, to the IIIcn nucleus- Edinger-Westphal nucleus
Where do parasympathetic fibres go after the Edinger-Westphal nucleus?
preganglionic fibres go to and synapse in ciliary ganglion, postganglionic fibres go through short ciliary nerves to constrictor pupillae and then there is pupillary constriction on both sides
Pupil abnormalities?
aniscocoria, pupils react differently to light
Causes of absent/ abnormal pupillary reflex
diseases of retina (detachment, degenerations or dystrophies), diseases of optic nerve (optic neuritis), diseases of the IIIcn (efferent limb)
What is ptosis?
drooping of eyelid
What is the conjunctiva?
A thin vascular membrane that covers the inner surface of eyelids and loops back over the sclera
What gland is affected in external stye?
sebaceous gland
What gland is affected in an internal stye?
meibomian gland
Name of corneal transplant?
keratoplasty
What is trabeculectomy and what is this surgery used for?
removal of a block of tissue in eye to allow AH to drain, used in glaucoma
What is normal position of eyelids?
top eyelid= hides top 2mm of cornea
bottom eyelid= at level of corneosclera junction
Right eye can’t adduct cause and when asked to look froward right eye looks medially?
6th nerve palsy
Ptosis and can only move eye laterally diagosis?
IIIcn palsy
Inferioir oblique overworking, can’t depress left eye
Left 4th nerve palsy
How can retinal detachment occur due to trauma?
peripheral retina to tear, vitreous gel gets liquified, liquid vitrous pushed through the retinal tear and detaches it
Drooping eyelid cause?
IIIcn palsy- due to LPS muscle
Inability to close eyelid cause?
Left VIIn palsy
Describe neuron cells
structural and functional unit, these are excitable cells that carry action potentials
Neuron= multiple dendrites and one axon
Describe glial cells
non-excitable supporting cells that are much smaller than neurons
What does the cell body of a nucleus contain?
nucleus (loose chromatin, prominent nucleolus), mitochondria, rER (nissl bodies), diffuse golgi apparatus
What is the difference in the cytoplasm in a cell body compared with an axon?
cytoplasm in the cell body is perikaryon and in axon is axoplasm
What is the myelin sheath formed by?
schwann cells in PNS
Oligodendrocytes in CNS
What type of matter would you find neuronal cell bodies?
grey matter
What type of matter would you find myelinated axons?
white matter
Types of neurons?
interneuron motor (multipolar) and sensory neurons (pseudounipolar) and olfactory mucosa retinal nerve fibres (bipolar)
Types of CNS glial cells?
Astrocytes (BBB)
Oligodendrocytes (myelination)
Microglia (phagocytosis, scar tissue formation)
Ependymal cells (line ventricles)
Types of PNS glial cells?
Schwann cells (myelination) Satellite cells (surround neuronal cell bodies
What are the lateral ventricles?
C-shaped cavities which lie in the cerebral hemispheres
Where does the 3rd ventricle lie?
in the diencephalon
Where does the cerebral aqueduct lie?
within the midbrain
where does the 4th ventricle lie and what is the shape of this ventricle?
between the pons and the medulla, and the shape is a diamond
What connects the 3rd ventricle with the lateral ventricles?
the interventricular foramen
what is found inside the ventricles?
CSF
What is found in the subarachnoid space and what layers of the meninges is this space between?
CSF
between the pia and arachnoid layer
Where is CSF formed?
by the choroid plexus in each ventricle
Where is CSF absorbed
by the arachnoid villi into the saggital sinus
Wjere are the receptors for the olfactory nerve?
in olfactory epithelium of the nasal cavity
What is the component of the olfactory nerve?
special sensory- smell
WHat is the component of the optic nerve?
special sensory- vision
name 2 clinical applications of the optic nerve?
increase in CSF pressure causes papilloedema, section of right optic nerve causes blindness through right eye
What is the component of the oculomotor nerve?
somatic motor- extraocular muscles and levator palpebrae superioris
visceral motor- parasympathetic to pupil causing constriction and to ciliary muscle causing accomodation of the lens
What is the clinical application of the oculomotor nerve?
drooping of upper eyelid, eyeball abducted and pointing downwards, no pupillaryreflex, no accommodation of lens
components of the trochlear nerve?
somatic motor- superior oblique
Clinical application of the trochlear nerve
diplopia when looking down
Abducent nerve components
somatic motor- lateral rectus
clinical application of abducent nerve
medial deviation of the affected eye causing diplopia
Components of the trigeminal nerve- ophthalmic division
general sensory- cornea, forehead, scalp, eyelids, nose and mucosal of nasal cavity and sinuses
Components of the trigeminal nerve- maxillary division
general sensory- from face over maxilla, maxillary teeth, temperomandibular joint, mucosa of nose, maxillarty sinuses and palate
Components of the trigeminal nerve- mandibular division
general sensory- from face over the mandible, mandibular teeth, temperomandibular joint, mucosa of mouth and anterior 2/3rds of tongue
somatic motor- muscles of mastication, part of diagastric, tensor veli palatinin and tensor tympani `
Clinical application of facial nerve
paralysis of muscle of mastication, loss of conreal or sneezing reflex, loss of sensation in the face, trigeminal neuralgia
What are the components of the facial nerve?
somatic motor- muscles of facial expression and scalp, stapedius of middle ear and part of digastric muscle
visceral motor- parasympathetic innervation of submandibular and sublingual salivary glands, lacrimal glands, glands of nose and palate
special sensory- taste from anterior 2/3rd of tongue and soft palate
general sensory-from external acoustic meatus
Facial nerve clinical application
bells palsy- cannot frown, close eyelid or bare teeth
Vestibulocochlear components
special sensory- vestibular sensation from semicircular ducts, utricle, saccule gives sense of position and movement
and hearing from spiral organ
Clinical application of vestibulocochlear
tinnitus, deafness, vertigo, nystagmus
What are the components of the glossopharyngeal nerve?
special sensory- taster from posterior 3rd of tongue
general sensory- cutaneous sensations from middle ear and posterior oral cavity
Visceral sensory- sensation from carotid body and carotid sinus
Visceral motor- parasympathetic innervation of parotid gland
somatic motor- to stylopharyngeus, helps with swallowing
Clinical application of the glossopharyngeal nerve
loss of gag reflex and taste from back of tongue
associated with injuries to CNs X and XI, this is known as jugular foramen syndrome
What are the components of the vagus nerve?
special sensory- taste from epiglottis and palate
general sensory- sensation from auricle, external acoustic meatus
visceral sensory- from pharynx, layrnx, trachea, bronchi, heart, oesophagus, stomach, intestine
Visceral motor- to pharynx, larynx, palate and oesophagus
Clinical application of the vagus nerve
damage to pharyngeal branches causing difficulty swallowing and damage to laryngeal branches causing difficulty in speaking
What is the component of the accessory nerve?
somatic motor- striated muscle of soft palate, pharynx and larynx, and to sternocleidomastoid and trapezius
Clinical application of the accessory nerve?
weakness in turning head and shrugging shoulders
Components of the hypoglossal nerve
somatic motor- to muscles of tongue
Clinical application of hypoglossal
vulnerable to damage during tonsillectomy
causes paralysis and atrophy of ipsialteral half of tongue, tip deviates towards affected side
Causes for gradual loss of vision?
cataract, glaucoma, age related macular degeneration, diabetic neuropathy
Causes for sudden loss of vision?
anterior ischaemic optic neuropathy- non-arteritic and arteritic
