Structure of Eyeball Flashcards
what are the components of the eye
- eyeball
- adnexa (ocular muscles, eyelids, lacrimal apparatus)
- housed in orbit (bony margins, copious fat)
what are the orientation of the eyeball
- poles
- optic axis
- equator
- meridian
name the structures
what are the 3 tunics of the eyeball
- external fibrous tunic
- middle vascular tunic
- internal nervous tunic
what is the function of the external fibrous tunic
gives shape to eyeball
protective
complete
what are the functions of the middle vascular tunic
blood vessels
smooth muscle
nutrient supply
control lens and pupil shape and size
what is the function of the internal nervous tunic
translation of visual signal into nerve impulses and transmission to brain
functional –> where light is converted into nervous signals
what is the fibrous tunic made up of
dense, collagenous
what are the functions of the fibrous tunic
resist internal pressure of material in chambers
gives shape to eyeball
what are the two parts of the fibrous tunic
- cornea
- sclera
meet at limbus
what is the cornea made up of
connective tissue –> lamellar/layered arrangement
what is the main part of the cornea
substantia propria
anterior and posterior lining epithelium
where are is the anterior epithelium
continuous with conjunctival epithelium –> contains sensitive nerves
responsible for corneal reflex
what is the posterior epithelium
continuous with anterior surface of iris
supplies nutrients to cornea (no vessels)
what is the basement membrane of the cornea
descemet’s membrane
last barrier to penetration of cornea (ulceration)
what is the sclera made up of
opaque/white
collagenous and elastic fibres
what is the function of the sclera
entry points for nerves and vessels
attachments for ocular muscles anterior to equator
what is the thin membranous covering that separates the eyeball from retrobulbar fat and what does it allow
vagina bulbi
allows eyeball free movement in socket
what are the 3 parts of the vascular tunic
- choroid
- ciliary body
- iris
what is the choroid
lines sclera from optic nerve to limbus
what is the ciliary body
thickening of tunic area at level of limbus
what is the iris
projects into cavity behind cornea
easily visible
what are the functions of the vascular tunic
- vascular supply
- suspends lens and controls shape of lens and pupil
- vessels enter eyeball at posterior pole and around equator
name the structures
what vessels are contained in the choroid
blood vessels in pigmented connective tissue
posterior ciliary arteries and vorticose veins
supplies nervous tunic via layer of capillaries
vessels seen with opthalmoscope
where is the avascular layer in the choroid
dorsal avascular layer between capillaries and larger vessels
what is the tapetum lucidum
reflective area –> sends light back through retina –> increases sensitivity of eye to low light
what is the ciliary body
thickened ridged ring around lens
what are the ciliary processes
extend zonular fibres to lens –> suspends lens
where is the smooth ciliary muscle and what is the function
between ciliary body and sclera
alters lens shape and alters lens focusing
what is the iris and where does it attach to
flat ring of tissue
peripheral attachment to sclera and ciliary body
what is the central opening of the iris
pupil
what muscles control the dilation/constriction of pupil
smooth spincter (constrictor –> parasympathetic) and radial dilator (sympathetic) muscles control pupil size
what does the pupil divide
anterior and posterior chambers
what are iridic granules
projections from dorsal border across pupil
horse, ruminant
what is part of the nervous tunic
retina
what does the retina line
choroid from optic nerve to pupillary margin
what are the parts of the retina that can be reached by light and what does it contain
posterior 2/3
contains receptor cells (pars optica retinae)
what part of the retina is not reached by light
anterior 1/3
has no receptors (pars ceca retinae)
continues onto iris
what is the pigmentation of the retina
black appearance of pupil –> absorbs light
what is the junction between optic and blind parts of the retina
ora serrata
level of junction between ciliary body and choroid
what is the optic disc
extension of brain arising from optic nerve
what are the retinal layers of the nervous tunic
- choroid
- pigmented epithelium
- neuroepithelial cells
- bipolar ganglion cells
- multipolar ganglion cells
what are the layers of the retina
where is the pigmented epithelium absent
no pigment over tapetum
what are the neuroepithelial cells
receptor cells
- rods –> B/W & night vision
- cones –> colour & day vision
what are the multipolar ganglion cells
axons pass to optic disc and form optic nerve
what inserts at the optic nerve
entry of optic nerve (CN II)
no receptor cells –> blind spot
easily seen with opthalmoscope
what is the area of the dorsolateral to optic disc
optimal resolution
macula
what is the visual axis
macula-centre of lens-object viewed
what is the refractive media
focussing of light through structure of eyeball
what are the components of the refractive media
- cornea –> major role in refraction of light
- aqueous humor –> anterior and posterior chambers
- lens
- virteous body –> virteous chamber
what is the aqueous humor and its function
clear, watery
maintains ocular pressure
what produces the aqueous humor
ciliary process cells –> enter posterior chamber
how does the aqueous humor enter and exit
anterior chamber via pupil
exits via iridocorneal (drainage)/angle (venous sinuses in sclera)
how is the aqueous humor drained and produced
drainage = production
constant intracular pressure
what does failure to drain aqueous humor cause
glaucoma
what is the lens
elastic
regularly arranged fibres –> transparency
outer capsule –> attachment of zonular fibres around equator (thickest part of capsule)
what is lens accomodation
lens will be thick if no external force –> circular ciliary muscle relaxed = wide circle )thin lens)
- muscle contracts –> relaxes zonular fibres (thick lens) –> close vision
- muscle relaxes –> tightens zonular fibres (thin lens) –> far vision
what is the process here (fibres involved, shape of lens)
what is the vitreous body
gel-like mass
high water content = vitreous humor
thin surface membrane
what is the function of the vitreous body
maintains contact between retina and choroid
hyaline artery passes to lens in embryo –> regresses after birth
what is the volume of the vitreous body
constant
not reduced/drained –> won’t cause pressure buildup
how can the eye be imaged
- opthalmoscope –> direct
- ultrasound (cheap, simple, allows assessment of retina)
- CT and MRI may be useful but more for orbital disease
what is the function of the adnexa
protect and move eye
what are the components of the adnexa
- orbit
- orbital fasciae
- ocular muscles
- eyelids
- conjunctiva
- lacrimal apparatus
what is the orbit
“conical” cavity on the lateral side of skull
what bones are in the orbit
frontal, lacrimal and zygomatic bones
which species have orbital ligament
carnivores and pig
what is in the orbit in horse and ruminants
zygomatic process
what are the openings of the orbit
- optic canal
- orbital fissure
- ethmoidal foraminae
- lacrimal sac fossa (leads to nasolacrimal duct)
what is the orbit lined with
fibrous sheets (periorbita) and fatty connective tissue –> allows free movement of eyeball
what are the structures of the orbit
what are the 4 rectus muscles
- dorsal
- ventral
- medial
- lateral
what are the 2 oblique muscles
- dorsal
- ventral
where do the ocular muscles originate from
optic canal area
what are the functions of oblique muscles
maintain orientation of visual axis
what are the functions of the ocular muscles
sheets of smooth muscle maintain eyeball protrusion and eyelid opening
what are the true eyelids called
palpebrae
what are the true eyelids
musculofibrous folds
upper and lower lids
meet at angles of eye (commissures)
what are the 3 layers of eyelids and conjunctiva
- skin
- musculofibrous
- mucous membrane = palpebral conjunctiva
what are these structures
what are the layers of the eyelids
- musculofibrous layer
- tarsus - fibrous plate
what is the musculofibrous layer
orbicularis oculi
orbital septum
levator palpebrae superioris
smooth muscles
what is the tarsus - fibrous plate
stabilizes edge of eyelid and gives shape to palpebral fissure
tarsal (meibomian) glands and cilia (eyelishes) along margin (secrete part of tear film)
what are the structures of the eyelids
what are the components of the conjunctiva
- palpebral conjunctiva –> lines lids
- bulbar conjunctiva –> reflects over sclera, epithelium anterior to cornea
what is the conjunctival sac
the space between lids and eyeball (spot for foreign bodies)
what is the 3rd eyelid
conjunctival fold –> central cartilage
conjunctiva on both sides –> not true eyelid
how is the 3rd eyelid retracted
by smooth muscle
orbitalis
covers eyeball when retracted into orbit
what is the function of the lacrimal apparatus
production of lacrimal fluid (tears) –> protection, corneal nutrition
what are the glands in the lacrimal apparatus
- lacrimal –> dorsolateral wall or orbit
- gland of 3rd eyelid –> around base of 3rd eyelid cartilage, deeper gland in pigs and cattle (AKA nictitans/nictitating gland)
which lacrimal gland causes cherry eye
inflammation of nictitans/nictitating gland
what are the glands
where is the drainage of tear film in the lacrimal apparatus
puncta lacrimalia
slits adjacent to caruncle
feed into lacrimal sac –> sacs drain into –> nasolacrimal duct –> runs through maxillan and drains into nasal cavity
where does the tear film pool at
at medial angle of eye –> lacrimal lake
fluid repelled from edge of lids by fatty secretion of tarsal glands
what are the 3 layers of the tear film
- outer: lipid, from tarsal glands (even spread of tears and integrity of film)
- middle: aqueous, from lacrimal glands (moisture, nourishment)
- inner: mucinous from goblet cells in conjunctiva (maintains film contact with cornea)
