Eye I & II Flashcards
What are the 3 layers of the eye?
- fibrous layer - corneoscleral coat
- vascular coat - uvea
- retina
What are the chambers of the eye?
anterior and posterior segments that further divide into different chambers
Describe the cornea of the eye
in the corneoscleral coat
- anterior 1/6 of the eyeball
- continuous with the sclera
- transparent and avascular
- provides 2/3s of refractive power
What are the five layers of the cornea?
1) corneal epithelium
2) Bowman’s membrane
3) corneal stroma
4) Descement’s membrane
5) corneal endothelium
What type of epithelium is corneal epithelium?
stratified squamous (non-keratinized) epithelium attached via desmososmes
What do apex of the corneal epithelial cells have that help retain tears secreted, preventing drying of the cornea?
microvili
What do corneal epithelial cells have that protect DNA from UV damage?
ferritin (melanin is absent)
What innervates corneal epithelium?
CN V1 (ophthalmic division)
- corneal blink reflex
- very sensitive
What is Bowman’s membrane?
acellular specialized basement membrane (anterior)
- does not regenerate
- teminates at corneoscleral limbus
What do Bowman’s membrane contribute?
- strength and stability of
cornea - acts as barrier to prevent spread of infections
What happens when Bowman’s membrane is damaged?
creates an opaque scar that can impair vision
What is corneal stroma?
90% of corneal thickness
What maintains the transparency of the cornea?
corneal stroma
- collagen fibrils arranged in lamellae where adjacent lamellae are arranged at right angles to each other
What are responsible for the precise spacing of the collagen fibrils in corneal stroma?
proteoglycans and collagen V
What happens when there’s a disruption to the lamellar arrangement of corneal stroma?
opaque cornea
What is Descemet’s membrane?
posterior basement membrane of the cornea endothelium (next layer)
- regenerates after injury
- thickens with age
- interwoven meshwork of fibers and pores
What does Descemet’s membrane help maintain?
normal curvature of the cornea through connections with the sclera and ciliary muscle
What type of epithelium is corneal endothelium?
simple squamous epithelium
Briefly describe corneal endothelium
- faces the anterior chamber of the eyeball
- epithelium is joined by zonula adherens, zonula occludens and desmosomes
- limited proliferative ability
What happens when corneal endothelium has been injured?
corneal opacity
Which layer of the cornea is responsible for virtually all of the metabolic exchanges of the cornea?
corneal endothelium
Briefly describe the sclera
- white part of the eye
- posterior 5/6s of the eyeball
- tough fibrous CT (collagen and elastic fibers) to maintain shpae of the eyeball
- Tenon’s capsule
- pierced by optic nerve, blood vessels and other nerves
What is the Tenon’s capsules?
fascial sheath over the surface of the sclera where the extraocular muscles insert
What is the corneoscleral limbus?
- location of stem cells for corneal epithelium
- location of iridocorneal angle
What is the iridocorneal angle?
- trabecular meshwork
- formation of the canal of Schlemm (scleral venous sinus)
- apparatus for the outflow of the aqueous humor
What does the uvea (vascular coat) contain?
- iris
- ciliary body
- choroid
Briefly describe the iris
- most anterior portion
- pupil
- anterior and posterior pigment epithelium
- contractile diaphragm in front of the lens (dilator and sphincter pupillae)
Where is ciliary body?
area anterior to the Ora serrata (defines the anterior limit of the retina and choroid and the posterior limit of the ciliary body)
Ciliary body is lined by which type of epithelium?
two layers of simple columnar epithelium separated by a basement membrane
What are the characteristics of the inner layer of ciliary body?
- adjacent to aqueous humor
- non-pigmented
- fluid-transporting epithelium
- complex cell-to-cell junctions
- well developed zonula occludens
What are the characteristics of the outer layer of ciliary body?
- pigmented, rich in melanin
- less developed cell-to-cell junctions
- ciliary channels
What are ciliary processes?
- 75 radial ridges
- secretion and anchoring zonule fibers, form suspensory ligament of the lens
Describe the flow of aqueous humor
posterior chamber > pupil > anterior chamber > trabecular meshwork > Canal of Schlemm > venous system
What produces aqueous humor?
ciliary processes
In regards to aqueous humor, what is blood?
aqueous barrier
Describe the ciliary muscle
- longitudinal fibers stretch choroid
- radial fibers flatten lens, distal vision
- circular fibers reduces tension on lens, near vision
Briefly describe the choroid
- dark-brown vascular sheet, prevents reflection of light waves entering
- lies between the sclera and retina
Why is the choroid dark-brown?
abundance of melanocytes
Briefly describe the choriocapillary layer
- inner vascular layer
- richer in small fenestrated blood vessels
- provides nutrients to the retina
What is the Bruch’s membrane?
aka Lamina vitrea
- thin, amorphous hyaline membrane
- innermost layer of choroid
- five layers formed from choroid and a retinal layer
What are the five layers formed from choroid and a retinal layer?
1) basal lamina of endothelial cells of choriocapillary layer
2) collagen fibers
3) elastic fibers
4) collagen fibers
5) basal lamina of the retinal epithelial cells
What does neural retina also known as?
retina proper
What are the 4 regions of neural retina?
1) non-photosensitive
2) photosensitive
3) optic disc (papilla)
4) macula lutea and the fovea centralis
Non-photosensitive region
- anterior to the ora serrata
- lines the inner aspect of the ciliary body and posterior surface of the iris
- non-visual portion
Photosensitive region
- posterior to the ova serrata
- pierced by the optic nerve
- most of retina is visual portion
Optic disc (papilla)
- site where optic nerve joins retina
- devoid of photoreceptors, blind spot
Fovea centralis
contains only cones (photoreceptor cell)
Which part of the retina has the greatest point of visual acuity?
Fovea centralis
Macula lutea
- “yellow spot”
- area that surrounds the fovea centralis
- 2.5 cm lateral to the optic disc
What is RPE?
retinal pigment epithelium
Why is RPE so heavily pigmented?
rods and cones are the photosensitive cells
RPE is attached to what?
attach through Bruch’s membrane to the choriocapillary layer of the choroid
What is meant by “detached retina”?
mechanical separation at the junction where RPE is attached through Bruch’s membrane to the choriocapillary layer of the choroid
What are the four groups of cells found in the retina?
1) photoreceptors
2) conducting neurons
3) association and other neurons
4) supporting (neuroglial) cells
What are the two types of photoreceptors?
rods and cones
What are the two types of conducting neurons?
bipolar and ganglion
What are the other neurons associated with cells of retina?
1) horizontal
2) centrifugal
3) interplexiform
4) amacrine
What are the supporting (neruoglial) cells?
1) Muller’s
2) microglial
3) astrocytes
What are the ten layers of the retina?
1) RPE
2) layer of rods and cones
3) outer limiting membrane
4) outer nuclear layer
5) outer plexiform layer
6) inner nuclear layer
7) inner plexiform layer
8) ganglion cell layer
9) layer of optic nerve fibers
10) inner limiting membrane
What kind of epithelium is RPE?
simple cuboidal
What are the functions of RPE?
1) absorption of light (prevent reflection and glare)
2) blood-retina barrier
3) participate in metabolic processes in the restoration of photosensitivity
4) phagocytosis and disposal of membranous discs from the rods and cones
Which part of the layer of rods and cones is the photoreceptive part?
polarized cells in apical portions
- specialized dendrites
Which is the most abundant photoreceptive cell?
rods
- low intensity light
What does the outer segment of the rods composed of?
flattened discs composed of two membranes, containing rhodopsin
What is rhodopsin?
visual purple that gets bleached by the light coming in
Which vitamin is needed for normal vision?
Retinal, vit. A derived from chromophore
- light causes conformational changes in retinal and converting it to retinol
- deficiency will lead to “night-blindness”
What is the function of inner segment of rods?
- metabolic machinery for biosynthetic and energy producing reactions of these cells
What separates outer segment from inner segment in rods?
connecting stalk containing cilium
What causes signal to be transmitted through the layers of the retina to the ganglion cells?
light induced hyperpolarization
Where are cones mostly found?
highly concentrated in the fovea centralis
What colors are cones sensitive to?
Iodopsin
- red, green, and blue
What’s the shape of the outer segment of cones? How is it different than rods?
Cones look like cones
Rods look like rods
Stacked discs of cones are stacked where?
stacked discs are attached to plasma membrane (differ from rods)
What is the function of inner segment of cones?
synthesizes proteins that are uniformly distributed throughout the outer segment (unlike rods)
What forms the outer limiting membrane?
Muller cells - not a true membrane
What’s in the outer nuclear layer?
cell bodies of rods and cones
What’s in the outer plexiform layer?
synapses between photoreceptor cells, bipolar cells and horizontal cells
What’s the function of bipolar cells?
summation of the signals from photoreceptor cells
What does low light intensity stimulate? How do bipolar cells summate signals?
retina
- at the peripheral region 100 rods are stimulated whereas at the macula lutea, 10 rods are stimulated
- bipolar cells will summate this and will lead to an impulse to the brain
- at the fovea centralis, one cone synapse with one bipolar cell
What’s in the inner nuclear layer?
nuclei of bipolar, horizontal, amacrin, interplexiform and Muller cells
What’s in the inner plexiform layer?
synapses between processes of bipolar, ganglion, interplexiform and amacrin cells
What’s in the ganglion cell layer?
cell bodies of multipolar ganglion cells
What does hyperpolarization of rods and cones cause in ganglion cells?
depolarization which then sends action potentials through axons into the brain
What’s in the layer of optic nerve fibers?
- axons of ganglion cells from the optic nerve
- optic disc “blind spot”, also point of exit for optic nerve
What’s in the inner limiting membrane?
basal laminae of the Muller cells
What’s the blood supply to the retina?
central retinal artery from ophthalmic artery
What are crystalline lens?
lens in posterior chamber of the anterior part of the eyeball
- biconvex, transparent and very elastic
- focuses light rays on the retina
- avascular
- no innervation
What are the three parts to crystalline lens?
1) lens capsule
2) subcapsular epithelium
3) lens fibers
Lens capsule
- basal lamina
- type IV collagen fibers and proteglycans
Subcapsular epithelium
- cuboidal layer of cells only on anterior surface of lens - connected by gap junctions
- gives rise to lens fibers at the equator
Lens fibers
- produced throughout life, rate decreases with age
- filled with crystallins (lens protein) causing cells to lose their nuclei and organelles
- cataracts, loss of transparency of the lens
- fibers stiffen and enlarge with age, Presbyopia, loss of accomodation
What’s the composition of vitreous body?
transparent gel, 99% water, 1% collagen, glycosaminoglycans and hyalocytes
What are the accessory structures of the eye?
1) conjunctiva
2) eyelids
3) lacrimal apparatus
What kind of epithelium does conjunctiva have?
stratified columnar epithelium with globet cells and basal almina overlying a loose connective tissue
What are the two parts of conjunctiva?
1) palpebral
2) bulbar
What is conjunctivitis?
pink eye
What do secretions of the conjunctiva produce?
tear film to protect cornea
What are the different parts of the eyelids?
1) tarsal plates
2) sweat glands of Moll
3) Meibomian (tarsal) glands
4) glands of Zeis
Sweat glands of Moll
apocrine glands open into eyelash follicles
Meibomian (tarsal) gands
sebaceous glands in the tarsus, open onto the free edge of the lid
What prevents rapid evaporation on the eyeball?
Meibomian glands and the tear film from conjunctiva
Glands of Zeis
smaller sebaceous glands open into eyelash follicles
