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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