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112 terms

Eye

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three layers of the eye wall
outer - corneoscleral coat
middle - vascular uvea
inner - photosensitive retina
space between the cornea and the iris
anterior chamber
space between the posterior surface of the iris and the anterior surface of the lens
posterior chamber
space between the posterior surface of the lens and of the neural retina
vitreous chamber
the anterior and posterior chambers contain a watery fluid called ___
aqueous humor
the ___ contains a transparent gel substance (hyaluronic acid and widely dispersed collagen fibers) called ___
vitreous chamber
vitreous humor
gives the eye its shape
vitreous humor
the outer or fibrous layer of the eye consists of the ___, the white portion, and the ___, the transparent portion
(these two layers are continuous)
sclera
cornea
___ is composed of dense, fibrous connective tissue that provides attachment for the extrinsic muscles of the eye
sclera
corneoscleral junction
limbus
an area of transition from the transparent collagen bundles of the cornea to the white opaque fibers of the sclera
limbus
- collagen bundles with interspersed fibroblasts
- nearly (but not completely) devoid of blood vessels
- bloodshot eyes are caused from dilated capillaries
sclera
protects cornea from UV, not melanin
ferritin
layers of the cornea
epithelium, NKSS
Bowman's membrane
corneal stroma
Descemet's membrane
endothelium, simple squamous
which layer of the cornea contains ferritin
epithelium
layer of the cornea that prevents spread of infections
Bowman's membrane
- thickest layer of the cornea
- collagen and elastic fibers with inerspersed fibroblasts
corneal stroma
basement membrane of the cornea
Descemet's membrane
secretes Descemet's membrane
endothelium, simple squamous
parts of the middle vascular uvea
choriod
ciliary body
iris
highly vascularized layer that provides nutrients for the underlying retina
choroid
highly vascular layer of connective tissue containing melanocytes that prevent the reflection of incident light
choroid
- contains pigment
- abundant melanocytes give its characteristic black colour
- makes pupil look black
choroid
anterior rim of the uveal layer continues forward, where it forms the stroma of the ___
ciliary body and iris
ring-like thickening of the choroid
ciliary body
within the ___ is the ciliary muscle
ciliary body
contraction of the ___ changes the shape of the lens, which enables it to bring light rays from different distances to focus on the retina
ciliary muscle
ciliary body has ~70 ciliary processes that form the ___ of the lens
suspensory ligaments
two layers of ciliary body epithelia
outer non-pegmented
inner pigmented
refraction by the lens
accommodation
accommodation is controlled by contraction and relaxation of the ___
ciliary muscle
___ of the ciliary muscle causes the lens to become thicker, now the eye is focused on near objects
contraction
___ of the ciliary muscle causes the lens to become flatter
relaxation
___ control accomodation of the lens to focus on near objects
ciliary muscles
regulates the amount of light that enters the eye
iris
- contractile diaphragm that extends over the anterior surface of the lens
- extension of the choroid
iris
___ forms the coloured, visible part of the eye in front of the lens
iris
contains smooth muscle and melanin-containing pigment cells scattered in the connective tissue
iris
- give eye its color
- block light entering eye except through pupil
melanocytes
in contribution of eye colour, fewest melanocytes give rise to ___ eyes and most melanocytes give rise to ___ eyes
blue
brown/black
activation of parasympathetic fibers to ___ (circular) muscles of the iris causes them to contract, decreasing pupil size
sphincter pupillae
activation of sympathetic fibers to ___ (radial) muscles of the iris causes them to contract, increasing pupil size
dilator pupillae
does the iris receive sympathetic or parasympathetic innervation?
both
the parasympathetic nerve fibers from CN III innervate the ___ as well as the ___ for lens accommodation
- pupillary constrictor (sphincter) muscles
- ciliary apparatus
- ___ inserts via the suspensory ligaments on to the periphery of the lens capsule
- regulates the shape of the lens
ciliary muscle
- ___ muscle of iris is a sphincter
- when contracted, constricts the pupil
circular
- ___ muscle of iris when contracted, dilates the pupil
radial
___ (facing posterior chamber) transports a protein poor plasma from fenestrated capillaries into posterior chamber of eye forms aqueous humor
- similar in ionic composition to plasma but contains less than 0.1%protein, compared with 7% protein in plasma
outer non-pigmented layer of ciliary processes
aqueous humor is produced by the ___
ciliary processes
___ is produced by ciliary epithelium in posterior chamber, flows into anterior chamber
aqueous humor
from anterior chamber, aqueous humor goes from ___ directly into the venous system
Canal of Schlemm
___ provides nutrients and oxygen for the lens and the cornea
aqueous humor
- damage to the optic nerve
- clinical condition resulting from increased intraocular pressure
glaucoma
___ can be caused by excessive secretion of aqueous humor or impedance of the drainage of aqueous humor from the anterior chamber
glaucoma
vision loss due to glaucoma is caused by damage to the ___
optic nerve
The entire surface of the lens is smooth and shiny, contains no blood vessels, and is encased in an elastic membrane, collagen type ___.
IV
the lens capsule is primarily ___ collagen
type IV
what are lens fibers?
cells that have lost their nuclei and organelles, becoming thin, elongated, transparent structures
where are crystallins found?
crystallins are found in lens fibers
___ are ...
- among the longest-lived proteins in the body
- formed in utero and persist for the life of the individual
- lens also keeps growing throughout life and also make new ___
crystallins
crystallins
lens capsule is a thick basement membrane containing ___ and ___
collagen type IV
laminin
loss of transparency of the lens or lens capsule
cataracts
___ that significantly impair vision can usually be corrected surgically by removing the lens and replacing it with a plastic lens
cataracts
innermost, photosensitive layer
retina
the chief refractive element in the eye
cornea
___ of the anterior and posterior chambers (minor role in difraction, however plays an important role in nourishing the avascular lens and cornea)
aqueous humor
2nd in importance to the cornea in diffraction
lens
minor role in diffraction
vitreous body
emmetriopia
normal, ideal
myopia
near-sighted
cornea is too thick or eyeball is too long
myopia
hyperopia
far-sighted
condition of unequal curvatures along the different meridians in one or more of the refractive surfaces (cornea, anterior or posterior surface of the lens) of the eye, in consequence of which the rays from a luminous point are not focused at a single point on the retina
astigmatism
in LASIK surgery, pulses from a computer-controlled laser vaporize a portion of the ___ and the flap is replaced
stroma of the cornea
in LASIK surgery, the cornea is made flatter to treat ___,
steeper to treat ___
and/or more spherical to correct ___ errors
nearsightedness
farsightedness
astigmatism
derived from inner layer of optic cup
neural retina
derived from outer layer of optic cup
pigment epithelial layer
- inner layer that contains the photoreceptors
- from inner cup
neural retina
- outer layer that rests on the choroid
- from outer cup
retinal pigmented epithelium
___ are specialized receptors for dim light
rods
- ___ specialized receptors for bright light reception
- also perceive color (3 types, each recognizes either red, green, or blue pigment)
cones
shallow depression located about 2.5 mm lateral to the optic disc
fovea
area of greatest visual acuity
fovea
Cones are highly concentrated in the ___
fovea
yellow-pigmented zone that encircles the fovea
macula
exit site for the optic nerve
optic disk
contains no photoreceptor cells and is called the "blind spot" of the retina
optic disk
- in rods
- molecules in the outer-segments discs absorb photons
rhodopsin
- in cones
- molecules in the outer-segments discs absorb photons
iodopsin
- rods
- photon absorption leads to the ___ of Na+ channels in the plasma membrane, which (hypopolarize/hyperpolarize)
the membrane and reduces the rate of inhibitory neurotransmitter release from the synaptic region
closure
hyperpolarize
chromatophore of rods is a vitamin A-derived carotenoid called ___, thus adequate intake of vitamin A is essential for normal vision
retinal
opsin + retinal =
rhodopsin
The process of breakdown activates the receptor protein which in turn, becomes able to activate a Gt protein, ___, bound to the inner face of the membranes of the photoreceptor discs. The activated G-protein releases the G-alpha subunit, to activate a cGMP phosphodiesterase, that breaks down cGMP
transducin
in rods, cGMP causes channels to ___, light results in their ___
open
closing
cell layers of the retina
horizontal
bipolar
amacrine
Müller's
ganglion
interspersed between photoreceptor cells and ganglion cells
bipolar cells
- synapse with the synaptic junctions between the photoreceptor cells and the bipolar cells
horizontal cells
processes of ___ branch extensively to provide sites of synaptic connections with axonal endings of bipolar cells and dendrites of ganglion cells
amacrine cells
- large, multipolar neurons
- axons of these neurons pass to the brain
ganglion cells
- neuroglial cells
- supporting cells for the neural retina
Müller cells
loss of vision in the center of the visual field because of damage to the retina
age-related macular degeneration
The ___ form of advanced AMD results from atrophy to the retinal pigment epithelial layer below the retina, which causes vision loss through loss of photoreceptors (rods and cones) in the central part of the eye
dry
drusen have a similar composition to ___ plaques, and their formation also seems to involve inflammation mediators
atherosclerotic
___ form of AMD causes vision loss due to abnormal blood vessel growth in the choriocapillaris, through Bruch's membrane, ultimately leading to blood and protein leakage below the macula
wet
Anti-angiogenics or ___ agents can cause regression of the abnormal blood vessels and improvement of vision when injected directly into the vitreous humor of the eye
anti-VEGF, anti-Vascular Endothelial Growth Factor
transparent mucous membrane that lines the inner surface of the eyelids and covers the sclera of the anterior portion of the eye
conjunctiva
inner surface of the eyelids
palpebral conjunctiva
sclera of the anterior portion of the eye
bulbar conjunctiva
The conjunctiva is a clear mucous membrane consisting of cells and underlying basement membrane that covers the sclera (white part of the eye) and lines the inside of the eyelids. It is composed of rare ___ epithelium
stratified columnar
___ is an inflammation of the conjunctiva usually associated with hyperemia and a discharge
conjunctivitis
- ciliary muscle fibers relaxed
- suspensory ligament taut
- lens ___ and focused for ___ vision
thin
distant
- ciliary muscle fibers contracted
- suspensory ligament relaxed
- lens ___ and focused for ___ vision
thick
close