MA7 - The Eye Flashcards
What is the limbus?
the site where the sclera and cornea merge
Loss of rods and cones leads to
loss of rods = night blindness
loss of cones = legal blindness
In which layer(s) are amacrine cells found?
cell body in inner nuclear layer
extends into inner plexiform layer
What structures are found in the ganglion cell layer?
cell bodies of ganglion cell neurons
specialized photosensitive cells (not rods and cones) that mediate circadian rhythms
Where does light enter the eye?
cornea
The corneoslcera is comprised of
cornea
sclera
What are the four functions of the cornea?
protection
structural support
filtration of undesirable wavelengths
focus image on retina
What structures are found in the nerve fiber layer?
axons of ganglion cells
majority of retinal microvasculature
Describe the constrictor pupillae.
arrayed circumferentially
causes pupil to become smaller when it contracts
What are bipolar cells?
interneurons that transmit signals from outer plexiform to inner plexiform layer
What is the significance of the tight junctions found in the outer limiting membrane?
contribute to the blood-retinal barrier
What are the three functions of the retina?
photoreception of images
transmission of images to optic lobe of brain
prevent backscatter of light
What structure connects the anterior and posterior chambers?
pupil
What is the function of ciliary processes?
provide attachment for zonules (inner epithelial cells)
What is the function of the lens capsule?
isolates lens from aqueous humor of posterior chamber
What kind of eptihelium is the corneal endothelium?
simple squamous
Describe the innervation and vasculature associated with the fovea. (2)
nerves servicing photoreceptors in fovea are distributed radially to fovea, so no nerves directly inside
no retinal blood vessels, so all support comes from choroid
Describe lens fibers.
post-mitotic and anuclear long, thin cells that span entire width of lens
Define photorefractive keratectomy (PRK). (3)
laser to correct mild-moderate myopia, hyperopia, and astigmatism
removal of corneal epithelium and then usage of lasers to reshape corneal stroma
replacement epithelium grows out from limbus
Differentiate between rods (3) and cones.
rods = more numerous than cones; absent in fovea; use rhodopsin
cones = 3 types, each of which produces a different iodopsin (blue, green, or red); concentrated in macula; only photoreceptor found in fovea
Ciliary muscle forms a ring around
the posterior chamber
Describe the appearance of endothelial cells of capillaries in the choroid, and why this appearance is important.
endothelial cells of capillaries in choroid are fenestrated and provide nutrients to RPE cells, which transport nutrients to rods and cones of retina
Ganglion cells have their cell bodies in the ganglion cell layer. Where are its dendrites and axons located?
dendrites = inner plexiform layer
axons = nerve fiber layer
From out to in, what are the components of the cornea?
stratified squamous epithelium
Bowman’s membrane (basement membrane)
stroma
Descemet’s membrane (endothelial basement membrane)
corneal endothelium
Describe the composition of the lens capsule.
capsule itself made of collagen and proteoglycans
its basal lamina is made of Type IV collagen
Which structure of the eye contains most of its vasculature?
uvea
What are the two primary functions of ciliary bodies?
control lens shape by changing tension on zonules via circularly oriented ciliary muscle
produce aqueous humor via inner epithelial cells on ciliary processes.
What is the function of the pigmentation in the outer epithelial cells of ciliary bodies?
blocks stray light
What is the relationship of the retina to the uvea/choroid?
RPE cells are attached to the choroid
rest of retina is plastered by hydrostatic pressure of vitreous body to RPE layer
What specific features demark the appearance of the limbus?
disappearance of Bowman’s membrane from cornea
appearance of vasculature from sclera
Describe the role of ciliary muscle in the eye’s focusing on objects. (5)
contractions constrict this ring → releases tension on zonules → lens adopts rounder shape → increases refraction → allows eye to better focus on close objects
Define myopia.
nearsightedness = impaired ability to focus on distant objects caused by cornea being too far away from retina
Describe the outer epithelial cell layer of ciliary bodies. (2)
pigmented
continuous w/ pigmented epithelial cells of iris and RPE
What is the function of the iris?
regulates amount of light that reaches retina
Where is the trabecular meshwork found in the eye?
junction of iris and limbus
What are horizontal cells?
interneurons that integrate signals from photoreceptor cells and influence signals between photoreceptor cells and bipolar cells
What is the most refractile part of the eye?
cornea
What structures are found in the inner plexiform layer?
dendrites of ganglion cells
axons/dendrites of bipolar cells
axons/dendrites of amacrine cells
Define and describe the optic disc.
site where optic nerve exits eye
no photoreceptors → “blind spot”
Neurologically speaking, why is the nerve fiber layer critical to eye function?
axons of ganglion cells in nerve fiber layer exit eye through opitc nerve and carry signals to thalamus → visual cortex o brain
What is the function of retinal pigmented epithelium (RPE) cells? (3)
maintain functionality of photoreceptor cells
melanin pigment prevents backscattering of light
phagocytose photoreceptor debris
What structure is responsible for the shape of the orbit?
sclera
(T/F) The iris has an anterior epithelium.
False. The iris only has a (highly pigmented) posterior epithelium.
What is a major structural difference between bipolar and horizontal cells?
bipolar cells extend into both inner and outer plexiform layers, but horizontal cells only extend into outer plexiform layer
Describe the epithelium of the conjunctiva.
continuous with skin and corneal epithelium
non-keratinized stratified w/ surface squamous, cuboidal, or low columnar
goblet cells in columnar areas
What structures are found in the myoepithelial layer of the iris? (2)
melanin
forms the dilator pupillae muscle
What is glaucoma?
loss of visual field, most commonly resulting from loss of ganglion cell neuron
What is the conjunctiva?
mucous membrane that lines inner surface of eyelids (palpebral conjunctiva) and eye surface (bulbar conjunctiva) of sclera
What is the macula lutea?
region of the retina with the highest density of cones (this region contains the fovea centralis)
What are canals of Schlemm?
open-ended circular vessels that carry aqueous humor from trabecular meshwork to venous system (via episcleral veins)
What is the function of the blood-aqueous barrier?
restricts movement of material from blood/interstitium to aqueous humor and vitreous body
What is the function of the corneal endothelium?
regulates and maintains stromal water content
When does onset of presbyopia occur?
40-50 years old
Describe the properties of the cornea. (4)
located centrally
where light enters
most refractile part of eye
most important for focusing images on retina
The uvea is composed of
iris
ciliary body
choroid
The iris determines eye color. Describe how melanosomes in the iris influence eye color.
lots of melanosomes = brown eyes
few = blue eyes
intermediate = green eyes
Define astigmatism.
aspherical cornea that leads to light rays not sharply focused onto retina
What is the sclera?
opaque, dense irregular connective tissue that forms white of eyes
Describe how the photoreceptor layer, containing rods and cones, is associated to the RPE layer. (2)
there is no physical linkage between the photoreceptor layer and the RPE layer
association is purely hydrostatic
Where do the photoreceptor cells synapse?
synapse with bipolar cells and horizontal cells in outer plexiform layer
Describe how ciliary bodies contribute to the blood-ocular barrier.
continuous capillaries in the ciliary body’s highly vascularized stroma have tight junctions that contribute to blood-ocular barrier
What instrument is used to view the retina?
opthalmoscope
Which structures contribute to the blood-ocular barrier? (2)
tight junctions in:
continuous capillaries of ciliary body stroma
inner epithelial cell layer of ciliary body
What is aqueous humor?
plasma-derived fluid that has less protein but more pyruvate/lactate than plasma
What is the function of the blood-retinal barrier?
restricts movement of materials from blood of retinal and choroidal capillaries to retina
Define laser-assisted in-situ keratomileusis (LASIK).
similar to PRK except that corneal epithelium is cut and peeled back to form flap prior to laser reshaping of corneal stroma
Define hyperopia.
farsightedness = impaired ability to focus on nearby objects caused by cornea being too close to retina
The retina belongs to which nervous system?
the retina is part of the central nervous system
What structures are found in the outer plexiform layer?
axons of photoreceptor cells
axons/dendrites of bipolar cells
axons/dendrites of horizontal cells
What are the two components of the blood-ocular barrier?
blood-retinal barrier
blood-aqueous barrier
What is the trabecular meshwork?
series of baffles that conveys aqueous humor from the anterior chamber to the canal of Schlemm
Define radial keratotomy (RK).
incisions near center of cornea to correct mild myopia
What are amacrine cells?
interneurons that regulate bipolar neuron transmission from photoreceptor cells to ganglion cells
(T/F) The sclera is contiguous with the corneal stroma.
True.
What are zonules?
elastic ligaments that connect basal lamina of inner epithelial cells of ciliary processes to the capsule of the lens
Differentiate between retinal and retinol use in the eye.
retinal = used by rhodopsin
retinol = used by iodopsin
What is the function of the lens?
aids focusing of nearby objects onto retina
What is the composition of the dilator pupillae?
myoepithelial cells
What is the outer limiting membrane?
membrane that separates outer nuclear layer (photoreceptor nuclei) from photoreceptor layer (rods and cones)
What are the three specialized regions of the retina?
macula lutea = area with cones
fovea centralis = center of macula
optic disc = site where optic nerve exits on orb
Where in ciliary bodies is melanin found?
outer epithelial cells
How are RPE cells connected to each other?
tight junctions
Which retinal layers contribute to the blood-retinal barrier?
RPE
outer limiting membrane
nerve fiber layer
Which structure of the eye is most important for focusing images on the retina?
cornea
The inner epithelial cells of ciliary bodies are connected by
tight junctions, which prevent leakage of fluid/macromolecules from posterior chamber into ciliary processes
Describe the properties of Descemet’s membrane. (2)
thick basal lamina of corneal endothelium
densely packed collagen fibrils to block diffusion of macromolecules b/w stroma and anterior chamber
What forms the blood-aqueous barrier?
inner epithelial cells of ciliary processes
endothelial cells of capillaries in contact w/ aqueous humor, mostly in iris
pigmend epithelial cells of uvea
Muller cells in inner limiting membrane
Define astigmatic keratotomy (AK).
incisions on steepest part of cornea to correct astigmatism
Aqueous humor is pumped into
the posterior chamber
What structures are found in the inner nuclear layer?
cell bodies of bipolar cells
cell bodies of horizontal cells
cell bodies of amacrine cells
cell bodies of Muller glial cells
Describe the structure of ciliary bodies.
disk-shaped with large, hollow core
lumen lined with ciliary processes
2 layers (inner and outer) of epithelial cells
What are the four primary components of the lens?
capsule
epithelium
lens fibers
zonules
Describe the epithelium of the lens.
simple cuboidal (only one cell thick) epithelium on anterior surface
Where are the nuclei of the photoreceptor cells located?
in outer nuclear layer (a layer of the retina)
Describe the dilator pupillae.
arrayed radially
causes pupil to enlarge when it contracts
What are the components of the iris?
pupil
posterior epithelium
myoepithelial layer
vascularized stroma
What are rods and cones?
the photoreceptor cells in the retina
Describe the inner epithelial cell layer of ciliary bodies. (2)
not pigmented
produces zonules (which are ligaments) anchored to its basal lamina that attach to the lends
What is presbyopia?
loss of lens elasticity
What is the inner limiting membrane?
innermost layer w/ basement membrane-like structure made by Muller cells that separates retina from vitreous body
Describe the properties of the uvea.
middle layer
What are cataracts?
loss of lens transparency
Inflammation of the cornea originates from
the limbus
What region of the retina has the highest acuity?
fovea
What is found in the outer nuclear layer?
cell bodies and nuclei of photoreceptor cells (rods and cones)
How are lens fibers connected to each other?
via gap junctions, which in essence forms a giant syncytium
What structure gives RPE cells their color?
melanocytes
What are the 10 layers of the retina, going from outside to in?
RPE cell layer
photoreceptor layer
outer limiting membrane
outer nuclear layer
outer plexiform layer
inner nuclear layer
inner plexiform layer
ganglion cell layer
nerve fiber layer
inner limiting membrane
What maintains the stroma of the cornea?
keratocytes, a type of fibroblast
List the properties of cones. (2)
color vision (RGB iodopsins)
most abundant in fovea
What are the effects of presbyopia?
loss of lens elasticity → lens can’t deform and focus → hard to see objects up close
Why do ciliary processes have to pump aqueous humor?
because hydrostatic pressure within ciliary processes is less than that in posterior/anterior chambers
The cornea is rich in what structures and lacks what structures?
rich in free nerve fibers
lacks blood vessels or pigments
What relays tension to the lens?
zonules
What structure produces aqueous humor?
ciliary processes of ciliary bodies
What causes glaucoma?
caused by excessive intraocular pressure (IOP) as result of excessive aqueous humor production or impaired aqueous humor outflow
Describe the relationship between the conjunctiva and vasculature.
conjunctiva has abundant vasculature in areolar connective tissue under epithelium
What is the sclera?
“whites of the eyes”
What is the significance of the tight junctions between RPE cells?
control passage of material between choroid and rest of retina (i.e. forms part of blood-retinal barrier)
What two muscles control the aperture of the pupil?
dilator pupillae muscle
constrictor pupillae muscle
What creates the outer limiting membrane?
Muller glial cells
Describe the properties of the corneal stroma. (3)
avascular, transparent connective tissue
alternating layers of keratocytes orthogonally arrayed with collagen fibrils
continuous with sclera
What are the three layers of the wall of the eye?
corneosclera - outermost
uvea
retina - innermost
Describe the characteristics of Bowman’s membrane. (4)
acellular
randomly arranged collagen fibrils
barrier to infection
does not regenerate if damaged
What is the composition of the sclera?
mucosa (conjuctiva)
stroma of dense irregular connective tissue
List the properties of rods. (4)
low-light vision
cannot discriminate colors
absent from fovea
use rhodopsin (GPCR)
What is the composition of the constrictor pupillae?
smooth muscle cells
What is the posterior epithelium of the iris?
layer of pigmented cells that blocks light and is rich in melanin
What controls the shape of the lens?
ciliary body, via relative constriction of ciliary muscle
Describe the highly vascularized stroma of the iris.
contains:
fibroblasts
macrophages
melanocytes
Which retinal layer contains the majority of the retina’s microvasculature?
nerve fiber layer
