Histology of the Eye
corneal epithelium, key structural aspect
"vermiform" ridges that retain tears
Be able to name the following on a pic of the eye: cornea, limbus, sclera, choroid, retina, optic nerve, central retinal artery, macula lutea, fovea centralis, anterior chamber, iris, canal of Schlemm, posterior chamber, lens, zonule fibers, ciliary body, ora serrata, vitreous body
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How does the fovea centralis differ from the rest of the retina? (2)
1 LESS LAYERS beginning with inner nuclear layer are angled away to allow greater visual acuity. 2 Single R&C stimulates SINGLE BIPOLAR neuron, which stimulates single ganglion cell. 3 NO BLOOD supply present in macula
retinal pigment epithelium (10th and outermost layer), fxns besides preventing light scatter (4)
1 absorbs light and prevents scattering, 2 phagocytose shed R&C membranes, 3 tight junctions form blood-retina barrier, 4 process Vit A, 5 pump ions
Name the ten layers of the retina.
1 inner limiting membrane, 2 nerve fiber layer, 3 ganglion cell layer, 4 inner plexiform layer, 5 inner nuclear layer, 6 outer plexiform layer, 7 outer nuclear layer, 8 outer limiting membrane, 9 layer of rods and cones, 10 retinal pigment layer
accessory glands of the eye, contributions to tears
1 lacrimal gland secretions (serous), 2 tarsal aka Meibomian gland secretions (oily), 3 goblet cells of conjunctiva secretions (mucus)
epith of ciliary processes, fxn (2)
1 secrete zonule fibers (suspensory lig of lense), 2 secrete aqueous humor
vessel-free zones of the eye? (2)
6 outer plexiform, 7 outer nuclear
sequelae, def
A condition that is the consequence of a previous disease or injury.
Name the area of the eye where the anterior chamber, posterior chamber, and vitreous body are located.
ANTERIOR ASPECT: anterior chamber, posterior chamber. POSTERIOR ASPECT: vitreous body. Dividing line between ant and post aspect is lens and zonular fibers.
Specify the layers where areterioles and venules (and capillaries) may be found.
ARTERIOLES: 2 nerve fiber layer. CAPILLARIES: 5 inner nuclear layer. VENULES: 4 inner plexiform layer.
Explain why the choriocapillary layer is particularly important.
Blood diffuses from this to the R&C.
vitreous body: composition (2), producing cells, macroscopic structure
Composed of loose collagen fibers, hyaluronic acid. Produced by hyalocytes (macrophages). Attached to retina posteriorly.
Describe the events occurring during accommodation.
For near-sighted, contraction of the ciliary body relieves the tension on the lens by the zonule fibers
9 rods and cones layer, contents
R&C
CLINICAL APPLICATION: Why can you see the dimmest stars by looking at them peripherally?
Rods are sensitive to low light and are much more numerous than cones. You have to look to the edge because rods are located peripherally.
Describe the blood supply of the eye (2), especially supply to and drainage from the retina.
Supply via 1 OUTER: choroidal vessels to retinal pigment epith and R&C, 2 INNER: retinal arteries from central retinal artery
What makes cones cone-shaped as opposed to rod-shaped?
The disks of their modified cilia are attached at one side, as opposed to rods which are free floating
fovea centralis vs. macula lutea, def
The fovea centralis (center hole) is the depression in the center of the macula lutea (yellow spot).
retinal artery vs. retinal vein bleed, pdx
VENULE: blood is confined due to vertical orientation of inner plexiform fibers. ARTERIOLE: blood spreads out horizontally due to orientation of nerve fibers in the nerve fiber layer
CLINICAL APPLICATION: What makes people have blue vs. brown eyes?
Varying densities of melanin; blue-eyed people still have brown pigment, but it reflects back as blue.
location where major bending of light takes place?
air-corneal interface
tarsal glands: aka, type of gland, fxn
aka Meibomian glands. Sebaceous glands. oily secretions reduce evaporation of tears.
lens fibers, structure (2)
anterior flattened cells with no nuclei and gap junctions
2 nerve fiber layer, contents
axons of ganglion cells
How does the modified cilium of R&C differ from a normal cilium?
basal body + 9x2 microtubules, but no central pair
CLINICAL APPLICATION: Retinal detachment occurs between which layers of the retina?
between 9 R&C and 10 retinal pigment epithelium
Describe the genral relationships of the ciliary body and iris.
both are extensions of the uveal (middle) layer and non-sensory retina. Their epithelium is continuous.
name of the canal that runs in the limbus?
canal of Schlemm
lens, structure (3)
capsule, ant epithelium, lens fibers
name of artery that runs through optic nerve?
central retinal artery
parts of the ciliary body? (3)
ciliary muscle, ciliary process, ciliary retina
ciliary body, structure
ciliary muscle, ciliary process, ciliary retina; smooth muscle and Na/K pumps. Attached to choroid.
lamina cribrosa becomes what as it goes back into the head?
continuous with the meninges
CLINICAL APPLICATION: Why do near-sighted people feel eye strain?
contraction of the ciliary body relieves the tension on the lens (a little counter-intuitive)
Compare the regenerative ability of the corneal layers. (5)
corneal epithelium (regenerates), Bowman's membrane (forms scars), stroma, posterior basement membrane (regenrates), corneal endothelium (does not regenerate)
Where is "conjunctiva" located and what is it continuous with?
corneal epithelium => bulbar conjunctiva (on eyeball) => palpebral conjunctiva
cornea, layers (5)
corneal epithelium, Bowman's membrane, stroma, posterior basement membrane, corneal endothelium
cells that produce the corneal stroma?
corneal fibroblasts
1 inner limiting membrane, contents
cytoplasmic processes of Müller's cell
Describe the structure of the optic nerve.
dark pink infoldings of pia arachnoid, may contain central artery, myelinated by oligodendrocytes of CNS
sclera, s&f
dense CT with penetrating blood vessels that supply choroid and retinal pigment epithelium, attachment point of extraocular muscles
dilator vs. sphincter muscle: fiber orientation, innervation
dilator is radial (sympathetic), sphincter is circular (parasympathetic)
trabecular meshwork, def
divides canal of Schlemm from anterior chamber
ora serrata, def
dividing point between sensory and non-sensory portions of retina, though epithelium is continuous
10 retinal pigment layer, contents
epithelium containing melanin pigment; 1 absorbs light and prevents scattering, 2 phagocytose shed R&C membranes, 3 tight junctions form blood-retina barrier, 4 process Vit A, 5 pump ions
lamina cribrosa, def.
extension of the sclera that accompanies the optic nerve where it exits
CLINICAL APPLICATION: diabetic retinopathy, pathophysiology
formation of new blood vessels (microvascularity) causes hemmorhaging
3 ganglion cell layer, contents. Continuous with what?
ganglion cells; source of optic nerve
uva, def
grape
rods and cones: s&f
inner segment and outer segment connected by modified cilium, cell body, then process that connects with horizontal and bipolar cell
limbus, def
interface between transparent cornea and white sclera
Why is the dense CT of the cornea transparent?
it is very orderly, perfect right angles prevent light scatter
As the ganglion cells of the retina exit the eye, at what point do they become myelinated?
lamin cribrosa
Describe the components of the choroid. (not in detail)
lots of capillaries right next to retinal pigment epithelium, serves as kind of a basement membrane for that layer
iris, structure
melanocytes, dilator muscle, sphincter muscle, epithelium only on the posterior aspect (anterior the stromal cells are exposed)
corneal endothelium, fxn
metabolic and water exchange to nourish stroma
Prominent organelles in R&C? (3)
mitochondria, rER, glycogen
Müller's cells: type of cell?
modified astrocytes
horizontal cell, fxn
modify transmission of information but do not transmit
5 inner nuclear layer, contents (4)
nuclei of bipolar cells (major), amacrine cells, Müller's cells, and horizontal cells
7 outer nuclear layer, contents
nuclei of rods and cones
eyelid, s&f
outer epithelium is thin skin, inner epithelium is conjunctiva (columnar epith with goblet cells)
Describe the general layered pattern of the eye (3) and list what is included in these layers. (2, 3, 3)
outer fibrous layer (sclera, cornea), middle vascular layer (choroid, parts of ciliary body & iris), inner retinal layer (retina, part of ciliary body, part of iris)
What structural aspects of the ciliary processes allow them to secrete aqueous humor? (3)
plasma membrane infolding, N/K pumps, tight junctions for blood-aqueous barier
membrane most likely to stop a knife to the cornea?
posterior basement membrane (aka Descemet's membrane)
PREVIEW: match rhodopsin and iodopsin with R&C
rhodopsin rod, iodopsin cone
How to distinguish peripheral nerve from optic nerve?
round shape, incomplete septa, no Schwann cells
traucoma, def
scarring of eyelids causes scarring of cornea
Describe the production, circulation, and fate of aqueous humor
secreted by ciliary processes into post chamber > travels through posterior chamber past the iris > ant chamber > through trabecular meshwork > Canal of Schlemm > aqueous veins
Describe convergence.
several rods or cones can synapse with a single bipolar neuron, several bipolar neurons can synapse with a single ganglion cell
anterior epithelium of lens, s&f
single layer of cuboidal cells that form new fibers at the equator (next to zonular fibers)
ciliary body: muscle type, epithelium type
smooth muscle (myoepithelium), double-layered PIGMENTED cuboidal epithelium (non-sensory retina beyond ora serrata)
regeneration of epithelium vs. endothelium of cornea
surface epithelium regenerates well, endothelium does not
zonule fibers: aka
suspensory ligament of lens
4 inner plexiform layer, contents (3)
synaptic layer; synapse between bipolar bipolar cell axons and ganglion cell dendrites. Amacrine cell processes also extend here.
8 outer limiting membran: contents, important structural feature
synaptic layer; synapse of Mueller's cells and R&C's (Müller's cells extend from inner to outer limiting membrane)
6 outer plexiform layer, contents
synaptic region; cytoplasmic processes of rods and cones synapse with next layer of cells
canal of Schlemm, fxn
takes aqueous humor from ant chamber, dumps it into venous system
adnexa, def
the parts adjoining an organ
CLINICAL APPLICATION: Glaucoma is a problem with which tissue of the eye?
trabecular meshwork is too thick, prevents flow of aqueous humor from ant chamber to canal of Schlemm
capsule of lens, structure
very elastic, thick basal lamina with collagen IV
CLINICAL APPLICATION: Why does the risk of retinal detachment increase with age?
vitreous body detaches from retina
Describe the general structure of the eye.
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