Microanatomy of eye Flashcards
What structure produces tear?
Lacrimal glands
What protective structures does the eye have?
- adipose tissue
- eyelids
- eyelashes
- fluid
- eyebrow
What are the black, coloured and white aspects of the eye called?
White - sclera
coloured - iris
black - pupil
What are the medial and lateral walls of the eyelid called?
medial and lateral commissures
What is the palpebral fissure?
area between either eyelid (eyelid also called palpebral)
What is the general function of the eye?
1) converts shape, colour and light intensity of objects into nerve signals which are sent to the optic nerve to create an image
2) focus
3) depth perception
4) balance
What is the lacrimal caruncle?
- located at medial wall of eye
- where glands open into the eye (enter via punctum)
What are the three layers of the eyeball wall?
- sclera (posterior) & cornea (anterior) - outer layer
- Uvea - middle layer
- Retina - inner layer
What structures make up Uvea?
1) iris (anterior)
2) Ciliary body
3) Choroid (posterior)
(all very vascular)
What do the cornea and sclera look like?
cornea - colourless
Sclera - opaque and white
What is function of the cornea and sclera?
Cornea
- responsible for lots of refractive properties (bends the light)
Sclera
- attachment site for intraocular muscles
Both
- protective
- maintain eyeballs shape
What structure is found between cornea and sclera?
- limbus
- zone of transition for the epithelium
Why is the Uvea pigmented and highly vascular?
- To block any light that is not coming through the pupil
- mediator of nutrition and gas exchange so lots of blood needs to move through
What are the two layers of the retina?
1) Outer pigmented (epithelial)
2) Inner retinal layer (photosensitive layer)
Photosensitive layer not present in anterior 1/3
What are the five layers of the cornea?
- Epithelium SSNK
- Bowman’s layer
- Stroma (collagen uniform and parallel to make transparent)
- Descemet’s membrane
- Corneal endothelium
What are the two aqueous chambers called and where are they located?
1) Anterior aqueous chamber (between cornea and iris)
2) posterior aqueous chamber (between iris and lens)
What glands secrete into the eye?
- accessory lacrimal glands
- Meibomian glands
- apocrine glands
What is the function of the conjunctiva?
- provide protection and lubrication of eye
- prevents microbial entrance
- produces mucus and tears
What happens to the choroid as you age?
blood vessels in choroid start to build up lipid deposits which can prevent diffusion of nutrients to retina
What is the function of the outer pigmented layer of the retina?
- pigment absorbs any extraneous light
- made up of RPE (retinal pigment epithelial cells) provide Vit A for photoreceptors
- RPE establish blood brain barrier with tight junctions
Where would you find vitreous body
fills the area between lens and optic disc
What is the function of the vitreous body?
- contributes to magnifying power of eye
- supports lens
- holds layers of retina in place
Why is the cornea dome shaped?
in order to bend the light passing through it
Which layer of cornea is most sensitive to damage?
bowman’s layer, will scar and lose visual acuity if damaged
epithelium able to heal itself
What parts of the eye will have contact with the tear film?
- cornea
- conjunctiva
What is Descemet’s membrane made up of?
collagen type 4
The iris is an extension of which part of the uvea?
Ciliary body which is a thicker part of the choroid
What is the pupil?
gap in centre of the iris (meaning iris can change size of pupil)
Describe the anterior epithelium of the iris?
- Double layered (anterior and posterior layer)
- anterior have contractile properties
- posterior heavily pigmented blocking light rays
Describe structure of ciliary body?
- ciliary muscle
- ## ciliary process come of muscle and extend toward lens
Describe the epithelium present in ciliary processes?
inner pigmented layer and outer layer unpigmented which secrete aqueous humour
What is the function of aqueous humour?
- assists in corneal refraction of light
- provides O2 and nutrients to lens and cornea
What pathway does the aqueous humour move through (from creation to drainage)?
1) created in ciliary processes
2) moves through iris to pupil and out again through pupil
3) into anterior chamber
4) drains through trabecular meshwork
5) trabecular meshwork drains into canal of Schlemm (venous system)
What is the problem with a blockage of drainage of aqueous humour?
- will increase pressure in eye
- can impede on optic nerve leading to vision loss
- can cause glaucoma
What are the layers of the lens?
- outer capsule (collagen T4)
- lens epithelium
- lens fibres (formed from lens epithelium cells which over time have been pushed back, lost their nuclei and been filled with crystallins to form fibres)
What condition is caused by accumulation of debris in lens fibres?
cataracts which is more common in diabetics becasue high glucose increases deposition
Function of retina?
convert photons of light picked up by neural retina into energy
Give examples of cell types found in sensory/neural retina?
1) Photoreceptor neurones - rods and cones
2) Conducting neurones - bipolar and ganglion cells
3) association neurones - horizontal and amacrine cells
4) neuroglial cells - Muller cells
What is the difference between rods and cones?
Rods
- more sensitive to light and motion
- very active at night
Cones
- sensitive to specific wavelengths of light (allow colour detection)
- used to assess spacial acuity
- larger diameter
What are the layers of the sensory retina?
Anterior
- Nerve fibre layer (axons of retinal ganglion cells)
- Ganglion cell layer (nuclei of retinal ganglion cells)
- Inner plexiform Layer (neurone synapses between axons and dendrites)
- Inner nucleus layer (cell bodies of glial, amocrine, bipolar and horizontal neuronal cells)
- Outer plexiform layer (neurone synapses between axons and dendrites)
- Outer nucleus layer (Cell bodies of R&C’s)
- external limiting membrane (Glial cells)
- Photoreceptor cells (R&C)
Posterior
What structure will the axon of retinal ganglion cells become?
optic nerve
Describe structure of the rods & cones?
1) outer segment (captures light and converts into electrical stimulus)
2) inner segment (contains most cell organelles e.g. mitochondria
3) Nucleus
4) Synaptic bouton
Cilium connects nucleus to inner segment and synaptic bouton
Where are most of the rods and cones located?
macula
cones concentrated in fovea
rods located more peripherally
What is the optic disc?
point at which axons from ganglion cells merge to form optic nerve
also known as blind spot as no photoreceptors
What is the two functions of the palpebrae?
- prevent entrance of foreign bodies
- help distribute tear film across cornea by blinking
Why does the cornea need tearfilm?
avascular so need tear film to get O2/nutrients
What is the function of the apocrine sweat glands/
add lysosome and other antibacterial agents to tear film
What does the conjunctiva add to the tear film?
contain goblet cells which make mucus secretions
What muscle is found in the eyelids
orbicularis oculi muscle
What is the tarsal plate?
fibroelastic tissue containing meibomian glands
What do meibomian glands secrete?
lipid rich secretion which prevent tears from evaporating
