wk 13, lec 3 Flashcards
which parts of the eye do focusing
EOMs (extra ocular muscles), ciliary body and ciliary muscles, iris
which parts of the eye do transparency
cornea, lens, aqueous and vitreous humour
which parts of the eye do transduction
retina
which parts of the eye do projection
sclera, conjunctiva
refraction depends on
how far object is from the eye
how is light focused
lens focuses light onto retina
size of pupil changes, why
to focus light onto retina; makes pinhole
transduction of light signals into 2D map action potential via
photons convert into electrical signals and send to brain
physical, chemical and infectious damage- protection in the eye
Sclera + fat in orbit
Lacrimal and mucosal secretions
Eyelids and lashes (cilia)
three layers (tunics) of the eye
- fibrous tunic
- vascular tunic (uvea)
3.retina (neurosensory layer)
what makes up the fibrous tunic layer of the eye
scelera and cornea
function of fibrous tunic
o Support eye shape, protections, EOMs attach to sclera
o Refraction
sclera
opaque or transparent? try of epithelium? vasculature or avascular?
opaque dense irregular CT- type I collagen, vasculature
cornea
transparent or opaque? how many layers? vascular or avascular? 2 names of membranes?
transparent and avascular, 5 layers
bowman membrane (barrier to infection)- epithelium
descement membrane – endothelium to keep hydrated and transparent
thick stroma- bundles of collagen (for transparency)
descement membrane in cornea for
keep hydrated and transparent
bowman membrane in cornea
barrier to infection
what is the name of the structure where the cornea and sclera merge
limbus
limbus (cornea and sclera merge) - what does it have? whats it a source of?
bulbar conjunctiva
source of stem cells
parts of the vascular tunic (urea)
choroid, ciliary body, iris
function of uvea
nutrients, absorb stray light
pupillary constriction and lens control
choroid- what type of membrane? vascular or avascular?
Vascularized with melanocytes to absorb light
Choroiocapillary lamina
Bruch’s membrane- collagen and elastin to separate retina from choroid
Bruch’s membrane function
- collagen and elastin to separate retina from choroid
cilia body is made of
ciliary muscles, ciliary processes, ciliary zonule
ciliary muscle connects
connects zonular fibrils via ciliary processes
ciliary processes
vascular, melanin to keep light from entering eye anywhere other than the pupil
ciliary zone
- Zonular fibrils for suspensory ligament of the lens
whats keeps light from entering eye anywhere other than the pupil
ciliary processes
what is accomodation
the ability of the eyes to focus on objects that are near or far.
retina (neurosesnroy layer) is for
o Signal transduction
o Initial processing of visual information
o Absorb stray light
in which compartment is aqueous humour made
anterior compartment
flow of aqueous humor
- Circulates in posterior chamber to anterior chamber (through the pupil) of anterior compartment
what secretes the aquesou humor
- Vascular ciliary processes sercrete aqueous humour from posterior chamber
functions of aqueous humor
carry metabolites, maintain envo for proper refraction
if drainage impaired of aqueous humor what happens
- If drainage impaired then increases intra-ocular pressure –> push back on retina and damage it
where is aqueous humor drained/resorbed
scleral venous sinus
how does scleral venous sinus drain/resborb aquesou humor
o Scleral venous sinus in limbus (where cornea and sclera merge)
o Trabecular meshwork to filter
what can block the scleral venous sinus
o Iris can flop over it and block it
iris is in what layer
- Anterior part of uveal (vascular) layer
what does the iris cover
- Covers part of the lens (doesn’t cover pupil)
iris is made of
- Fibroblasts and melanocytes
deep layer of the iris has
- Deep layer has myofibroblasts and 2 muscles for pupil size
2 muscles in iris
dilatory pupillae and sphincter pupillae muscles
Dilatory pupillae muscles- PNS or SNS? found where?
o Dilatory pupillae muscles- SNS, along most of iris
Sphincter pupillae muscles- PNS or SNS? found where?
PNS, along central iris
dilatory vs sphincter pupillae muscles
o Dilatory pupillae muscles- SNS, along most of iris
o Sphincter pupillae muscles- PNS, along central iris
vitreous body- transparent or opaque? made of? attaches to?
- Transparent, gel like CT in posterior cavity
- 99% water (also collagen fibrils and hyaluronate)
- Halocytes build the ECM
- Attaches to surface of retina at inner limiting membrane
in embryology, what is retina made of
outpouching of diencephalon
cells and barrier in retina
o astrocytes, microglial, muller cell (specialized glial cell)
o blood-retina barrier
how many layers in the retina
- nine layers
o inner= close to vitreous
o outer= close to choroid
rods and cones of the retina function
transduce light information (NT release)
bipolar cells, ganglion cells, axons of ganglion cells function in the retina
line of communication from rods and cones to the optic nerve
horizontal cells and amacrine cells function in the retina
: interneurons that modify activity of many things
pigment epithelium in the retina function
support rods and cones, lie on Bruch’s membrane
how does optic nerve and rods and cones communicate
via bipolar cells, ganglion cells, axons of ganglion cells:
where are the most amount of rods found? cones found?
o Most cone [ ] at fovea
o Most rods in rest of retina
physiologic blind spot
no photoreceptors over optic nerve
what embryo structure is the lens derived from
ectoderm
is lens transparent or opaque
transparent
lens fibers have what is periphery vs centre
o Viable cells at periphery, center has mature lens fibers that lost nuclei and become packed with crystallins
presbyopia
loss of elasticity in lens with age
cataracts
opacities in the lens
acommodation in the lens for distant vision
lens flattens or rounds? ciliary muscle contract or relax?
lens flattens, ciliary muscle relaxes and ciliary body holds ciliary zonule taut
acommodation in the lens for near vision
lens flattens or rounds? ciliary muscle contract or relax?
ciliary muscles contract, change shape of ciliary body, relax tension on ciliary zonule, lens becomes more rounded
photoreceptor cells that release NTs
rods and cones
- Light passes through cornea and enters the eye through the _____. The size of this structure is mediated by the ______.
- Light passes through cornea and enters the eye through the pupil. The size of this structure is mediated by the iris.
- Light is bent (refracted) as it passes through the various structures of the eye, but it is the _____ that can change its shape to focus the beams on the retina.
- Light is bent (refracted) as it passes through the various structures of the eye, but it is the lens that can change its shape to focus the beams on the retina.
refraction
bending of light
where does refraction focus the light onto
- Focused onto retina to see one image
refraction flips the image how
- Image of object in visual field is projected upside down and inverted on retina – brain flips it back up (i.e. top visual field to bottom of retina, bottom visual field to top of retina, right field to left side of retina, left field to right side of retina)
what changes shape to control the amount of refraction
lens
what structure bends the most light
cornea
if there was no refraction
beam goes straight through, scattered on retina and would see multiple images
how does lens change shape for refraction when object is close
more convex (rounded) lens means beams are bent more
distant objects not refracted because?
o Divergent beam from distant object doesn’t enter the eye so doesn’t need to be refracted
Distant objects doesn’t need to be refracted because light is coming in parallel
accomodation
process the eye uses to focus on nearby object
3 parts of accomodation
- increase convexity (round lens)
- converge eyes (move inward)
- constrict pupil (miosis)
what is convexity round lens controlled by SNS or PNS
PNS
what happens for the lens to round
o Oculomotor nerve fire, ciliary muscle contracts, suspensory ligaments (ciliary zonule) relax –> lens rounds
what happens to lens if object is distant
muscle relaxed, ligaments tight, lens flat
what happens to eye when something is near
muscle contracted, ligaments loose, lens rounded
convergence of the eyes (move inwards) via what
o Oculomotor nerve, medial rectus muscle
pupils constrict (miosis) via PNS or CNS and in bright or dark
o PNS control (oculomotor nerve stimulates pupillary sphincter of íris = constrict)
o In bright light
miosis is
pupils constrict
mydriasis is
pupils dilate
pupils dilate (mydriasis) in light or dark and PNS or SNS?
Pupils can also dilate (mydriasis)
Fight/ flight, dim light
SNS control (sympathetic nerve stimulates radial pupillary muscles of iris= dilate)
which muscle for miosis (pupil constrict) and which for mydriasis (pupil dilate)
miosis- opupillary sphincter of iris
mydriasis- radial pupillary muscles of iris
2 conditions of the lens
myopia (near sited)
hyperopia (far sited)
what happens in myopia or hyperopia
- Inability to focus beams from distant objects when lens is flat (i.e. ciliary muscle relaxed)
myopia (near sited) and hyperopia (far sited) is if eyeball to long or short
myopia- eyeball too long
hyperopia- eyeball to short
myopia (near sited)
o Cant see things in distance
o Distant beams converge before retina
hyperopia (far sited)
o Cant see things up close
o If lens were flat, distant beams converge after retina
o Can see distant objects because those light rays are relatively parallel and eye can accommodate it
visual acuity - what is 20/20 (normal) mean
o First value= furthest readable distance of chart for patient in feet
o Second value= furthest readable distance of chart for person with normal vision in feet
- 20/18 = better than normal
- 20/30= worse
how is the strength of a corrective lens measured in
diopters
what is used to correct hyperopia (far sited, cant see up close)
convex lens
what is used to correct myopia (near sited, cant see far away)
concave lens
convex (+) lens cause beams to
converge
concave (-) lens causes beams to
diverge
depth perception is affected by 3 things
- moving parallax
- access to previous knowledge
- steropsis
moving parallax
o apparent shift in the position of an object relative to a background as the observer changes their viewpoint or moves
stereopsis is
o binocular disparity: eyes apart so have different view and causes retina disparity so brain puts information back together
o fixed focus point projects to fovea of both eyes (no disparity)
o closer object projects to different places on each retina (retina disparity)
use retinal disparity of two objects to contribute to depth perception
closer= greater retinal disparity
binocular disparity causes
stereopsis
fixed focus point to create
no disparity in eyes
retina disparity is greater when
object closer
what is in the pigment layer of the retina that is key for photoreception
vitamin A/ retinal
rods and cones are for what type of vision
rods for night vision
cones for colour vision
pigment layer
contains melanin to prevent diffuse scattering of light
contains vitamin A to help rods and cones with photoreception
layer of retina with rods and cones
contains outer segment of rods and cones
have photopigment to absorb light and begin the transduction of visual signals to the brain
outer limiting membrane in retina
seperates outer segments of rods and cones from their cell bodies
outer nuclear layer of retina
contains cell bodies of rods and cones (nucleus, organelles)
outer plexiform layer of retina for
transmission of visual signals from the synaptic terminal portion of rods and cones to other cell types (bipolar, horizontal cells)
inner nuclear layer contains
the cell bodies of other cells involved in the transmission and modulation of visual signals (bipolar, horizontal, and amacrine cells)
inner plexiform layer
transmission of visual signals among bipolar, amacrine, and ganglion cells
ganglion layer of retina contains
cell bodies of ganglion cells
nerve fiber layer of retina contains
optic nerve fibers (axons of ganglion cells) to carry visual signals to brain
inner limiting membrane in retina is
boundary between retina and vitreous humour
blindspot (optic dics) contains and doenst contain what
cant see stimuli because no photoreceptors (rods or cones) here, only optic nerve
3 parts of rods and cones
outer segment
inner segment
synaptic terminal
where is the outersegment of rods and cones
in pigment/ photoreceptor layer
where is inner segment of rods and cones
in nuclear layer
where is synaptic terminal or rods and cones
in outer plexiform layer
outer segment of rods and cones contains
photopigments and vitamin A
inner segment of rods and cones contains
cell body (nucleus and organelles)
synaptic terminal of rods and cones releases what
glutamate for signal transduction
rods and cones
which has good visual acuity and which doesnt
rods: - poor visual acuity, highly convergent circuits (i.e. 5 rods go to 1 cell), not found in fovea
cones: - good visual acuity, circuits not highly convergent (1 cone to 1 cell), highly concentrated in fovea
rods and cones
which has good night vision and which doesnt
rods: - good night vision because contain high photopigment (only need 1 photon of light to be activated)
cones: - poor night vision because lower photopigment (need 100 photos of light for activation)
rods and cones
which has good colour vision
rods: - no colour vision because no colour photopigments
cones: - good colour vision; lots of colour photopigments
visual acuity via which strucutre
fovea
where are cones found and rods not found that makes them have visual acuity
in the fovea
rods in the periphery
short wavelengths for which colour
blue
medium wavelengths for which colour
green
long wavelengths for which colour
red
wavelengths and colours
- S (short wavelengths) – blue
- M (medium wavelengths) – green
- L (long wavelengths) – red
- Other colours may stimulate ratios of these 3 colours
- Tree appears green because light not absorbed, its reflected back
- White= no light absorbed
- Black= absorb all light
2 types of colour blindness
anomia and anomaly
anomia is
missing a type of cone (dichromy)
anomaly is
having a defective type of cone (less sensitive) (trichomy)
red and green colour blindness can be from
- Protanopia and protanomaly:
- Deuteranopia and deuteranomaly:
blue yellow colour blindness from
- Tritanopia and tritanomaly
protanopia and protanomaly are
: red cone issue
o Red-green colour blindness
- Deuteranopia and deuteranomaly
: green cone issue
o Red-green colour blindness
- Tritanopia and tritanomaly:
blue cone issue
o Blue-yellow colour blindness
colour blindness
- Protanopia and protanomaly: red cone issue
o Red-green colour blindness - Deuteranopia and deuteranomaly: green cone issue
o Red-green colour blindness - Tritanopia and tritanomaly: blue cone issue
o Blue-yellow colour blindness
red green colour blindness
genetic?
- Red-green colour blindness is x linked recessive, can’t distinguish spectrum of green through red
blue yellow colour blindness is genetic? what does blue/green look like and what does yellow/ orange look like
- Blue- yellow colour blindness is autosomal dominant
o Blue/green looks grey and yellow/orange looks pink
photopigment components (2)
chromophore component and opsin component
photopigments in rods and cones are in
the saccules/ disc of the outer segment
chromophore component of photopigments are made out of
o Chromophore component= retinal/ vitamin A
what does chromophore component do
Pigment that captures light and induces conformational change in opsin component
opsin component of photopigments are a
GPCR
opsin component function
signal transduction
what is the photopigment in a rod and in a cone
rod= rhodopsin
cone= lodopsin
rhodopsin photopigment in rods: light? colour?
o Sensitive to light
o Doesn’t detect colour
lodopsin photopigment in cones: light? colour?
o Not sensitive to light
o For colour
L (long) = red, M (medium)= green, S (short)= blue
signal transaction in rods when its dark (opposite to when its light)
cis-retinal open Na+ channels rod depolarize increase Glu hyperpolarize and inhibit of “on- center” bipolar cells
signal transduction in rods in response to light
- Rhodopsin captures light; converts cis- to trans-retinal
o Activates rhodopsin to meta-rhodopsin - Meta-rhodopsin activated GPCR
o G protein= transducin
Phosphodiesterase and cGMP - G-protein closes Na+ channel
o Hyperpolarize
o Decrease glutamate release
o On-center bipolar cells are depolarized/excited
o Bipolar cells communicate to brain via optic nerve to sense the light
signal transduction in rods in response to light simplified
- rhodopsin makes cis to trans retinal
- meta rhodopsin activates transducer GPCR
- open Na+ channel to hyper polarize
- decrease glutamate
- excite and depolarize on-center bipolar cells = see light
