neuro - week 2 Flashcards
Where is the fovea located relative to the Optic Nerve?
nasally
Posteriorly, what are the layers of the eye? (3)
Outside to in: Sclera –> Choroid –> Retina
What is peripapillary?
near or around the nerve head in the eye
What is papilledema?
swollen nerve head in the eye
What structure drives the refractory power of the eye?
Cornea
What are the layers of the cornea? (5)
Epithelium –> Bowman’s membrane –> Stroma –> Descemet’s membrane –> Endothelium
What are the functions of the cornea? (2)
1) major refractive structure (50 D)
2) Protects eye from environment
What are the characteristics of the Epithelium of the cornea?
Types of cells?
characteristic?
Types of cells: stratified squamous cells
Characteristic: high regenerative capacity/heals quickly
What are the characteristics of Bowman’s membrane?
What is it made of?
Function/characteristics? (2)
Made of: acelleular layer of unorganized collagen fibers
function: barrier to infection
characteristic: can heal, but scars can form
What is the stroma?
Made of?
Function? (2)
Made of: organized type 1 collagen bundles
Function:
1) binds water to maintain corneal clarity
2) contributes to variation in corneal thickness
What is Descemet’s membrane?
Description?
function? (2)
Description: The basement membrane of the endothelium of the cornea
Function:
1) helps keep the stroma clear
2) Increases thickness with age
What is the Endolthelium of the cornea?
Cell type?
Function?
Cell type: simple squamous epithelia
function: pumps water out of stroma
What is Myopia?
Name?
location of focal point?
Name: nearsightedness
Location of focal point: anterior to retina
What is Hyperopia?
Name?
Location of focal point?
Name: farsightedness
location of focal point: posterior to retina
Why is vision more clear when pupil is small?
A small pupil limits the point spread function and wave aberrations of your eye.
What are the three parts of the Uvea?
1) Choroid
2) Ciliary body
3) Iris
What are the layers of the choroid? (3)
Out to in:
Vessel layer –> Choriocapillary layre –> Bruch’s membrane
Why does the choroid have melinin?
Regulates light coming into the eye by absorbing light that doesn’t go through the pupil.
Which areas does the Ciliary body contact? (3)
1) Vitreous body
2) sclera
3) posterior chamber
What is the function of ciliary processes?
Increases surface area to secret the aqueous humor
What is the limbus of the eye?
Where the nearly opaque sclera transitions to transparent cornea
What is the Trabecular meshwork?
Location?
Function?
Location: within ciliary body near the LIMBUS
Function: aqueous humor is drained from anterior chamber via the trabecular meshwork
What is the main function of the Iris?
to regulate the amount of light entering the eye
What are the parts of the iris? (4)
1) anterior aspect
2) posterior surface
3) dilator pupillae muscle
4) sphincter pupillae muscle
What are the characteristics of the anterior aspect of the Iris?
Made of?
Function? (2)
Made of: vascular, loose CT with interspersed melanoctyes
Function:
1) melanocytes absorb light that doesn’t go through the pupil (you want to restrict light to go only through pupil)
2) melanocytes also determine eye color
What are the characteristics of the Posterior surface of the Iris?
Made of?
Function?
Made of: double layer of pigmented epithelium
Function: absorbs light
What are the characteristics of the dilator pupillae?
Cell organization?
Function?
Innervation?
Cell organization: radially arranged myoepithelial cells
Function: Contraction leads to dilation of eye
Innervation: sympathetic
What are the characteristics of the sphincter pupillae muscle?
Organization?
Function?
Innervation?
Organization: concentric smooth muscle bundles at the pupil margin
Function: contraction constricts the eye
Innervation: parasympathetic
What is heterochromia?
Where does it manifest?
Why is it important?
Heterochromia is having multiple colors in the same iris.
Manifests in the anterior aspect of the Iris
Could be a sign for pathology unless it was there since birth
Where is the anterior chamber of the eye?
Between the lens and cornea
What is the purpose of the anterior chamber? What does it contain?
Purpose: involved in maintaing intraocular pressure
Contains aqueous humor and is avascular
Where is the posterior chamber?
In between the Ciliary body and Lens, Posterior to the Iris
What is the pathway of aqueous humor flow?
From ciliary processes –> posterior chamber –> anterior chamber –> trabecular meshwork –> Schlemm’s canal –> veins of sclera
What are the types of glaucoma?
1) open angle
2) angle closure
What is Open Angle glaucoma? Why is it called that?
The trabecular meshwork is not absorbing aqueous humor well so pressure builds up.
It’s called Open angle because there is a nice path for the aqueous flow to go from posterior to anterior chamber
What is Angle closure glaucoma? Why is it called that?
The Iris is butted up against the trabecular meshwork, therby closing that angle and not allowing aqueous humor to flow from the posterior chamber
When would it be dangerous to dilate a patients eye?
If they have Angle closure glaucoma
What are clinical signs of Glaucoma?
1) elevated Pressure
2) visual field defects starting in the PERIPHERY
What is Lamina Cribrosa?
Network of collagen fibers through which fibers of the optic nerve exit the eye
May be altered in glaucoma
What are the structural components of the lens? (3)
1) Capsule: ECM surrounding lens
2) Epithelium: anterior surface
3) Lens fibers: body of lens with no organelles
What are the functions of the Lens? (2)
1) second to cornea in refractive power
2) accommodation
How does the lens change shape in accommodation? (thickness, focus, ciliary muscles, zonule fibers)
Thinner = focused on distant objects = relaxed ciliary muscles = tight zonule fibers
Thicker = focused on near objects = constricted ciliary muscles = loose zonule fibers
What are cataracts? How are the types? (3)
Clouding of the lens
1) nuclear cataract: located in the center of the lens
2) cortical cataracts: layer surrounding nucleus
3) posterior capsular cataract: found in the back outer layer of lens
Which cataract develops most rapidly?
posterior capsular cataract
What is the Vitreous body?
made of? (2)
function? (2)
Made of: acellular - major macromolecules are type 2 collagen and hyaluronic acid
Function:
1) transparent
2) nutritive function
What are the layers of the Retina?
Ganglion –>Inner plexiform –> Inner nuclear –> Outer Plexiform –> Outer Nuclear –> rods/cons –> pigment epithelium –> choroid –> sclera
(choroid and sclera not part of retina)
What is the inner limiting membrane (ILN)?
The ILN separates the retina from the virtuous humor
How can you tell what part of the retina is being imaged?
At fovea?
Central near fovea?
Peripheral?
At fovea: Ganglion cells, Inner plexiform and inner nuclear layer will be absent
Central near fovea? all layers present and ganglion layer thickest
Peripheral? all layers present but ganglion layer is thinner the further away from fovea
What are the layers of photoreceptors? (3)
Inner segment –> connecting cilium –> Outer segment
What is the function of the inner segment of photoreceptors?
protein synthesis and energy production
What is the function of the connecting cilium of photoreceptors?
transport of proteins (10 billian opsin molecules per second)
What is the function of the Outer segment?
Flattened membrane discs with photosensitive visual pigments (opsin)
What is the difference between the structures of Rods and Cones?
Rods: long slender outer segment
Cones: conical outer segment with discs
What are the structural characteristics of the foveal? (3)
1) No inner layers (ganglion cells, inner plexiform and nuclear layer)
2) Lots of cons and no rods
3) avascular
How does the size of cons change as you move away from fovea?
inner segments of cones get bigger
What are the functions of the Retinal Pigment Epithelium (RPE)? (6)
1) absorbs scattered light (melanin)
2) transports nutrients and ions between photoreceptors and choriocoapillaris
3) spatial buffering of ions
4) reisomerization of all-trans retinal
5) outer segment renewal
6) secretion of growth factors
What is the ratio of photoreceptors to RPE cell?
40 photoreceptors to 1 RPE cell
How are photoreceptors renewed? When is peak activity for cones? When is peak activity for rods?
an RPE cell engulfs and digests 10% of the mass of each outer segement per day
Peak activity for cone shedding: dusk
Peak activity for rod shedding: dawn
What is age related macular degeneration? (AMD)
Cause?
Type of vision loss?
“dry” vs “wet” version?
Cause: Drusen develop within Bruch’s membrane as you age
Vision loss: Vision loss is slow, central vision deteriorates first
“wet” version: Drusen cause a break in bruch’s membrane or RPE and you get neovascularization from the choroid
What two branches of the opthalmic artery supply the eye? What parts of the eye do each supply?
Retinal artery system (30%): supplies inner retina
Ciliary artery system (70%): choroid
What is Albinism?
Oculocutaneous albinism? (OCA)
Ocular albinism? (OA)
Symptoms?
OCA: no pigment anywhere
OA: no pigment in eye, normal skin and hair
Symptoms: universal visual problems and foveal hypoplasia
What is foveal hypoplasia?
arrested development of the fovea, occurs in albinism
What is the ratio of Rods to cones?
20 rods for every cone
What are the following characteristics of Rods?
Sensitivity? speed/integration time? spatial resolution? pigmentation? directionally selective?
Sensitivity: more sensitive speed: slow (integration time = 100 msec) spatial resolution: poor pigmentation: more directionally selective: no
What are the following characteristics of Cones?
Sensitivity? speed/integration time? spatial resolution? pigmentation? directionally selective?
Sensitivity: less sensitive speed: fast (integration time: 25 msec) spatial resolution: high pigmentation: less directionally selective: yes
Which photoreceptors can saturate?
Only rods, cons can not saturate
How do photoreceptors respond to light?
hyperpolorize
What are photopigments made up of? (2)
1) chromophore (11-cis retinal)
2) opsin (protein component)
What wavelength does chromophore normally aborbe?
375 nm
What is the purpose of opsin?
Opsin “red shifts” the absorption spectrum of chromophore
What are the three types of cones?
small - blue
medium - green
large - red
What type of light do rods absorbe optimally?
blue-green
Which type of cone receptor is their the least of?
small - blue
What is the principle of univariance?
Photoreceptors are unable to disambiguate different wavelengths. “the output depends on quantum catch, but not upon which quanta are caught”
What are the steps in phototransduction?
1) a photon isomerizes chromophore (11-cis to all trans) and releases opsin
2) opsin activates transducin
3) transducin activates PDE6 (phosphodiesterase type 6)
4) PDE converts cGMP to GMP
5) low cGMP closes ion channels
6) cone hyperpolorizes
How do you convert all-trans retinal back to 11-cis retinal so to be able to respond to another photon?
all-trans retinal is shuttled to the RPE by inter-photoreceptor retinol binding protein (IRBP) where it is converted to 11-cis and shuttled back
What is the role of inter-photoreceptor retinol binding protein (IRBP)?
Shuttles all-trans retinol and 11-cis retinol between RPE and photoreceptors
Which type of photoreceptor degenerate first in retinal diseases and why?
Cones have a back up way of getting 11-cis retinal (muller glia cells supply it) so they can survive for longer
Which type of phosphodiesterase are in the retinal cells?
PED5
What type of cone is most likely to be disrupted by PDE inhibitors?
the blue (small) cones because their are much fewer of them
What does it mean that photoreceptors are “OFF Centered cells”?
Photoreceptors respond to a photon by hyperpolorizing and releasing less neurotransmitter.
What type of cells are bipolar cells? (2 types)
1) Off-center cell: stimulus in the center of its receptive field causes cell to hyperpolorizes and reduces the cells release of NT (sign conserving synapse)
2) On-center cells: stimulus in the center of its receptive field causes cell to depolarize and release more NT (sign reversing synapse)
What types of synapses do “On-centered” bipolar cells have with the cones?
sign?
type of contact?
type of glutamate receptor?
response to glutamate?
sign: sign reversing
type of contact: invaginating contacts on to cones
glutamate receptor: metabatropic receptor
response to glutamate: hyperpolorizes
What types of synapses do “Off-centered” bipolar cells have with the cones?
sign?
type of contact?
type of glutamate receptor?
response to glutamate?
sign: sign conserving
type of contact: flat/basal contact on to cones
Type of receptor: ionotropic receptor
response to glutamate: depolorizes
What is the purpose of parallel pathways?
Improved sensitivity.
What type of response do the following cells have (graded release of NT or action potential?)
Photoreceptors?
Bi-polar cells?
Ganglion cells?
Photoreceptors: graded release of NT
Bi-polar cells: graded release of NT
Ganglion cells: action potential
What are the various types of ganglion cells and types of sign? (2)
1) on-center (sign conserving)
2) off-center (sign conserving)
What types of anatomical types of ganglion cells are there? (2)
Parasol and Midget
What are the characteristics of Parasol ganglion cells?
Size?
Receptive field?
projection?
type of response?
Size: Large
Receptive field: large
projection: magno layers
type of response: more transient
What are the characteristics of Midget ganglion cells?
Size?
Receptive field?
projection?
type of response?
Size: small
Receptive field: small
Projection: parvo layers
type of response: more sustained
What percentage of ganglion cells are Parasol and Midget?
Parasol: 10%
Midget: 90%
What are photosensitive melanopsin RGC?
Description?
Purpose?
receptive fields?
Description: These ganglion cells have their own melanopsin so they can respond to light without the help of photorecpetors.
Purpose: responds to ambient light, believed to have a role in sleep/wake cycles
receptive fields: large
What are horizontal cells?
laterally interconnects all the photoreceptors and causes lateral inhibition
What neurotransimter do horizontal cells release?
GABA
What is the purpose of lateral inhibition?
Improved resolution by enhancing edges
What is rhodopsin?
The protein component of the rod photopigment
What is Retinitis Pigmentosa (RP)?
Cause?
Symptoms?
Cause: mutation in Rhodopsin (does not tolerate polymorphisms)
Symptoms: night blindess (rods affected first), periphery to center defects
What is Usher’s syndrom?
Most common form of deaf-blindness.
Involves defects in proteins involved in the connecting cilium and sensory ciliary of the ear, which is why it causes both blindess and deafness
What can cause color vision defecets?
one of the cone systems is missing
What is achromatopsia?
lacks cone function so they can’t see color. Caused by a mutation in cyclic nucleotide gated channel for the cones, so they can’t respond.
patients get photophobic because their rods are saturated
What are some characteristics of congenital color vision defects?
Level of severity?
eyes affected?
visual acuity?
incidence?
Severity: same throughout life
eyes affected: both eyes affected equally
visual acuity: often unaffected
incidence: higher in males
What are some characteristics of acquired color vision defects?
Level of severity?
eyes affected?
visual acuity?
incidence?
Severity: type and severity fluctuates
eyes affected: monocular differences often occur
Visual acuity: often reduced
incidence: equal in males and females
