Retinal Transduction Lec11 Flashcards
what is the fovea? the small depression at center of macula with the ___
highest spatial acuity
what enters and leaves the optic disk?
blood vessels enter and retinal axons leave the eye
: ant. ciliary and long post. ciliary arteries supply blood to the
iris and ciliary body
Uveal tract consists of three structures:
choroid, the ciliary body and the iris.
Delivery of metabolic substrates and oxygen to the retina is accomplished by (2)
the inner retinal and choroidal.
what is the posteriro chamber
Region between the vitreous and the lens.
what produces aqueous humor?
the vascular component of the ciliary body.
where is the vitreous humor
the space between the back of the lens and the surface of the retina.
what pigment does the macula contain?
a yellowish pigment (xantophyl). Supports high acuity.
The ocular vessels are derived from the
all from the ophthalmic artery (OA),
what are the two distinct vasciualr systems that supply the eye
a) the anterior segment (iris and ciliary body)
b) the retinal systems.
Focusing Power of a lens =
Curvature of surface + differences in Refractive Indexes
focal length - how strongly a lens ___
converges light.
Greater lens curvature = Greater converging power = __ focal length
Shorter
diopters - measure of
optical power.
dipopeter =
1/focal length
emmetropic eye - is
elaxed, unaccommodated, focused on object at “infinity”
what is responsible for most of the refraction in the eye
Cornea - 80%
lens does 20%
Refractive index of cornea =
1.37
accommodation - the___ to focus on near objects
curvature of the lens increases
what muscles contract to increase the curvature of the lens? which relax?
ciliary muscles contract, zonule fibers relax
when the curvature of the lens increases the focal length
decreases
Accommodative triad/near reflex:
eye accomm. + pupil constriction + eye convergence
eye accomm. + pupil constriction is mediated by the
parasymp. nerves from Edwin Westphal nucleus of pretectum
The ___ lens is transparent, has crystallins, with high refractive index of 1.42,
crystalline
• cataract - disorder of___ that destroys lens transparency,
lens cell fibers or aggregation of crystallin
___ is the leading cause of blindness worldwide.
cataracts
risk factors for cataracts
aging, diabetes, sunlight, smoking
sx of cataracts
hazy vision, poor night vision, glare, faded colors
tx of cataracts includes
surgical replacement with an artificial lens
presbyopia - inability to focus on _____ objects
near
Refractive errors prevent light from
focusing on the retina
myopia / nearsightedness is caused by the
cornea too curved or eyeball too long
with myopia the light is focused ___
in front of the retina
nearsightedness is called
myopia
with -hyperopia / farsightedness the cause is the
cornea not curved enough or eye too short
with hypoerpopnia the light is focused
behind the retina
you correct hyperopia with
(+)/convex lens
you fix myopia with a
concave lens
Aqueous humor nourishes the__ and ___
cornea and lens
aqueous fumor is secreted by the
epihtelium
Aqueous humor
flows from anterior chamber angle of eye
to…
Leaves the eye by passive flow at the anterior chamber angle
Flow of aqueous humor against resistance generates ___.
intraocular pressure (IOP) of ~15 mmHg
Glaucomas = damage to the ___ that can result in vision loss and blindness
optic nerve
risk factors for glycoma
high IOP, thin cornea, abnormal optic nerve, HTN, cardiovascular disease, diabetes
glaucoma causes loss of ___ fields
peripheral
tx of gluacoma?
treat with
- eyedrops to decrease aqueous production or increase drainage
or
- surgery
where are photoreceptor cell bodies found?
outer nuclear layer
order light passes through to get to the photoreceptor
- ganglion cell layer
- inner plexiform laer
- inner nuclear layer
- outer plexiform layer
- out nuclear layer
cells in inner plexiform layer
bipolar / amacrine / ganglion cells synapse
cells in inner nuclear layer
bipolar / amacrine / horizontal cell bodies
cells in outer plexiform layer
photoreceptor / bipolar / horizontal cells
function of pigment epithelium?
backstop for light, regenerate pigment, nourish and regenerate photoreceptors
pigment epithelium in the back of the eye contains ___ pgiment
melanin
a lens with a short focal length has ___ focal power
greater
Focal distance is ___ proportional to the curvature of the lens.
inversely
loss of ___ with cage causes presbyopia
lens elasticity
A diopter of accommodation is defined as
1/distance to the object
. A near object at 1 m requires accommodation of ___
1 D
1/ ( distance to object)
___ requires a positive lense
hypermetropia (positive is a convex lens)
Myopic correction using the excimer laser is based on a graded removal of____ tissue to decrease the central anterior corneal curvature.
central anterior corneal
___ correction is based on a graded removal of a peripheral and paracentral anterior corneal curvature.
Hyperopic
glaucoma
Open angle: Slow development of pathology caused by obstruction of the___
drainage canals
glaucoma
Close angle: Sudden increase in intraocular pressure. Closed or___
narrow angle between the iris and cornea.
where does phototransduction occur
in the outer photoreceptor segments
photic input is transmitted to the brain by the spiking discharge pattern of the____ via the optic nerve.
ganglion cells
Retinal glia cells include
astrocytes
microglioa
mueller cells
Vertical information flow:
photoreceptorsbipolar cellsganglion cells
Lateral information flow:
Is mediated by
horizontal cells and amacrine cells
Cells along the vertical path (photoreceptors, bipolar and ganglion cells) release ___
glutamate
Cells mediating lateral information transmission (horizontal and amacrine cells) release mostly
GABA or glycineric
rods and cones are ___
photoreceptors
rods and cones use what NT
glutamate
Photoreceptors in the ___ have a standing/circulating current
Dark
Dark
__ and ___ influx at outer segment: depolarization
Ca and Na
Dark
___ at inner segment: hyperpolarization
K efflux
in the dark, the photoreceptor is constantly
staying depoalrized and -40 and releasing glutamate
Photoreceptors respond to Light by suppressing the ___
inward, cationic current
rhodopsin = pigment in ___
rods
cone opsin = pigment in ___
cones
Photon absorption makes 11-cis retinal to
all-trans
11-cis retinal to all-trans, activates –>
rhodopsin (rods) or opsin (cones)
Rhodopsin* initiates signal cascade (via transducin and PDE) that___
decreases cGMP
1 Rhodopsin ___ lots of cGMP –> closes 200+ cGMP channels
hydrolyzes
↓ cGMP in outer segment –>
Na and Ca gates close
how does light cuase less Glu release?
Rhodopsin dec cGMP > Na and Ca gates close -
-> ↓ Na and Ca influx (but K efflux continues) –> h
yperpolarization –> ↓ Glu release & ↓ intracellular Ca
____ is the ability of photoreceptors to adjust to the ambient level of light
Light Adaptation
light adaption occurs in Occurs in __ and ___
photoreceptors & in postsynaptic retinal cells
what happens at saturation?
all cGMP-gated channels are closed, photoreceptors cannot respond to further light
rods are cones are very senstiive to light
rods
mutation in rod proteins causes ___
retinitis pgimentosa
night blindess, tunnel vision, often legally blind by 40 are sx of
retinitis pgimentosa
1 cone to __ bipolar cell
1
rods have a much higher convergence
rods or cones mediate high acuity vision?
cones
wet
blood vessels behind retina grow and leak
dry
degeernation of epithelium and photorceptors, causing dursen build
age related macular degeration
lose: central vision and acuity
age related macular degeration
LGN enters V1 and terminates in___
layer 4
Ouputs to higher areas of v1 is by ___
pyramidal cells
