Review of ocular structure and function Flashcards
What are the 4 tissue types in the body
- Nervous
- Muscular
- Epithelial
- Connective
What are the three types of muscular tissue
- Skeletal
- Smooth
- Cardiac
What are the two types of epithelial tissue
- Covering
- Glandular
What are the two types of connective tissue
- Loose
- Dense
What can glandular exocrine glands be split into
- Unicellular glands
- Multicellular glands
What is example of unicellular gland
Goblet cells
What are multicellular glands divided into
Simple ( one duct )
Compound ( several ducts ) - bundles of secretory cells
Each duct has secretory units
What is meant by exocrine
secrete into duct
What is meant by endocrine
secrete into blood system
how many layers is tear film made of
3
what are layers of tear film
- mucin layer - mucous - stick rest of tear film onto cornea
- aqueous layer - serous secretions - bulk of tear - middle
- lipid layer - sebaceous secretions - outer - stop rest of tear film evaporating
What is example of simple multicellular gland
tarsal gland - found in upper and lower eyelids
They open onto the ocular surface via pores at the eyelid margin
what part of tear film do tarsal glands secrete
Sebacceous - oily component
What forms the mucous part of tear film
Conjunctival goblet cells - cover posterior ( back )surface of eyelids and exposed surface of eye (limbus)
What does conjunctiva contain
mucous secreting goblet cells
What do goblet cells have
triangular nucleus + large lumen
What is example of multicellular compound gland
Lacrimal gland
what part of tear film does lacrimal glands secrete
Aqueous component - serous secretions
Process of blinking
Secrete tear film into conjucitval sac
All secretions spread over eye
Spreads tear film over eye’s exposed surface when we blink
Tears drained over puncta into lacrimal sac and then nose
What are tears drained through
Puncta
What are tears drained into
nasolacrimal duct
What are the main muscles involved in opening and closing the eye - movement of eyelids
Two skeletal muscles
Voulantary
Where do part of the muscles lie
Part of the muscle lies within the face and part within the eyelid
What are two muscles involved in moving eyelids
- Orbicularis Oculi
- Levator palpebrae superioris
What does the Orbicularis Oculi
Runs around the eye Closes the eye Orbit = round Oculi - eye Its contraction closes palpebral aperture ( eyelid )
What does Levator palpebrae superioris do
Runs along top of eye ball and sends tendons into eyelid
Opens eye and raises upper eyelid when it contracts
what is an example of a dense regular connective tissue
The corneal stroma
What is corneal stroma made of
collagen
is corneal stroma transparent or opaque and why
transparent
due to tightly packed and regularly arranged collagen fibres
What is outer corneal layer known as and where is it located
Corneal epithelium
Front of eye
What type of epithelium is it and why
Stratified squamous
Protects from dirt, eyelids,
What is the inner surface of the cornea known as
Corneal endothelium
What type of epithelium is corneal endothelium and why
Simple squamous
Single layer of flat cells = diffuse easily across barrier of minimal thickness
Ideal for areas where exchange of substances is required - allows avascular cornea to exchange substances with aqueous
Where does light enter after travelling across cornea
Anterior chamber - filled with aqueous humout
Lens
Vitreous humour
Impinges on retina
What does the light sensitive retina do
Converts photons to neurobiological activity
Where is posterior chamber
infront of lens, behind iris
what is the outer coat of eye known as
sclera
is sclera opaque or transparent and why
Opaque - white
collagen fibres irregularly arranged
What is the corneoscleral junction known as
Limbus
what is connective tissue proper made of
- fibres ( collagen, elastic and reticular )
- cells ( fibroblasts…)
- ground substance
what are fibres
long stringy proteins in viscous brown substance
what is connective tissue divided into
loose - adipose or aereolar
dense - regular - specific order, same diameter
or irregular - randomly arranged, varying diameters
How many layers does cornea have and what are they
5 epithelium bowmans layer stroma descemets membrane endothelium
how many muscles does iris contain and what are they
2
iris sphincter
iris dilator
what does iris sphincter do
circular muscle that constricts/closes pupil when sphincter contracts
parasympathetic pathway
what does iris dilator do
opens the pupil when it contracts
sympathetic pathway
what is ciliary body divided into
- anterior ridge pars plicata- folded
- posterior smooth thinner pars plana - simple
what are pars of plicata made up of
series of ridges - ciliary processes
what does ora serata do
flat bit of ciliary body merges with retina here
what is ciliary process covered with
2 layered epithelium
what is outer pigmented epithelium part of
eye’s black box effect
what is inner unpigmented epithelium part of
aqueous humour - produces it
what is closest to inside of eye from inner unpigmented epithelium and outer pigmented epithelium
Inner unpigmented epithelium
How does the black box effect work
stops stray light bouncing off retina = seeing detailed images
dont want light bouncing around inside of eye
open eye - black on inside - heavily pigmented
What is uvea made up of
iris - forms pupil - merges with….
ciliary body
choroid
What is choroid
a vascular layer - blood vessles sandwiched between sclera and retina
function of choroid
main function to supply nutrients to outer retina
why does outer retina need nutrients
it contains no nutrients itself - no blood vessels
what is bruch’s membrane
separates choroid and retina
what happens if bruch’s membrane is dusrupted
age related macular degeneration
pars of plannner
flat/thin
pars of plecata
folded/pleated
where is choroid in histological section
to the left of anterior eye
where is iris
coming of ciliary body - front of anterior eye
What is iris
forms pupil
‘offshoot’ of ciliary body anteriorly
acts as aperture stop
where does light go through in eye
pupil ONLY
What is posterior surface of iris covered with and why
2 layered epithelium containing melanin
ensures the only light that enters eye is through pupil - light cant get through body of iris = aperture stop
what is iris made of
loose areolar connective tissue - iris change size
what is stroma example of and why
loose areolar connective tissue
change shape as pupil size changes by 2 muscles
how is lens attached to ciliary body
by suspensory ligaments
what are 3 layers of lens
- elastic lens capsule covering entire surface - outer layer
- simple epithelium underneath this
- bulk of lens is made of elongated cells ( lens fibres ) - long thin cells
what are lens fibres
long hexagonal cells that run from front to back surface of lens
how are adjacent lens fibres joined
by gap junctions = allow flow of nutrients
Aqueous production of inner epithelium of ciliary body
aqueous travels from ciliary body, past lens and supplies avascular lens and cornea with nutrients
it is drained through the trabecular meshwork into the canal of Schlemm at filtration angle
what happens if aqueous is not drained
eye eventually explodes - glaucoma
what is aqueous humour produced by and what does it do
inner epithelium
provides nutrients - need it because lens + cornea are avascular - no blood supply
what does canal of schlemm do
takes in used aqueous and recycles it into avascular system
summary of aqueous production
- aqueous into anterior chamber
- comes to filtration angle
- trabecular framework - filters through aqueous humour and comes in canal of schlemm where it drains and recycled into vascular system
what is bulk of ciliary body made of
smooth ciliary muscle
what is bulk of ciliary body made of
smooth muscle - contracts - ciliary body moves inwards - towards lens - changes focus of eye
what does inner layer of ciliary body do
produces aqueous
what does outer layer of ciliary body do
black box effect
what is the function of the lens capsule
- elasticity - accommodation
- selective barrier to substances - stopping large matter e.g. inflammatory cells entering lens, while allowing smaller necessary metabolites through
- cataract surgery
what happens in cataract surgery
- the lens stoma is ‘ liquified ‘ by an ultrasound probe ( destroys lens fibres )and sucked out leaving capsule behind like empty bag which is then filled with an artificial lens
i. e. replace damaged lens fibres with plastic lens = replacement lens - in capsule
why is most of total refractive index provided by the cornea
due to the difference between the refractive index of air and the cornea
role of lens
fine focus image through accommodation - change power
provides little refractive power
where is majority of focusing of light done and why
at border of cornea
because its curved and the difference in refractive index between air and cornea
when is eye usually emmetropic
at rest ( parallel light rays from distant objects focused on retina ) - light not refracted
where are close objects focused
behind retina
what is accommodation
bring close objects into focus - eye increase its refractive power - bend light more to refract more
what happens in unaccommodated eye
lens is under tension and pulled flat
ciliary muscles relax and lens stretched
what happens in accommodated eye
tension on lens released
rounder shape/fatter
ciliary muscles contracts
move closer to lens = more powerful
what is presbyopia
loss of accommodative ability with age
what is retina
lines back of eye
terminating anteroraly at ora serrata
made up of various neurons and glial cells
convert light into neurobiological activity
what are outer layers of retina composed of
- photoreceptors - convert optical image into nervous potentials ( phototransduction )
what are cones sensitive to
high light levels
what are rods sensitive to
low light levels
what are the 5 main types of neurones the retina is made up of
- photoreceptors
- horizonal cells
- bipolar cells
- amacrine cells
- ganglion cells
what is the end result
action potential generated in ganglion cells
what does light do
light traverses the inner retinal neurons before reaching photoreceptors
electrical signals leave via ganglion cell axons - make up optic nerve
where is highest quality of image produce
fovea - because cones close together
what are the 6 muscles attaching eyeball to skull
- superior rectus
- superior oblique
- medial rectus
- lacteral rectus
- inferior oblique
- inferior rectus
