Microanatomy of the Eye- Lecture 35

what are the 2 areas of the retina?

nervous and non-nervous

describe the importance of light not being able to directly hit the non-nervous retina

no photoreceptors or neurons in that region of retina

_______ is highly pigmented and very vascular

uvea

what are the 3 layers?

-fibrous

-vascular

-nervous

what is the fibrous area in most of the eye?

sclera

what is the vascular area in most of the eye?

uvea

what is the nervous area in most of the eye?

retina (nervous and non-nervous)

what do the 3 distinct layer of the nervous retina correspond to?

nuclei of photoreceptors and of neurons

how do you differentiate nervous and non-nervous retina?

-non-nervous: about 2 layer

-nervous: about 7 layers

sclera is continuous with the _______

cornea

the uvea is continuous with the _______

iris

describe the cornea

epithelium on anterior side of the cornea transitions to the epithelium of the bulbar conjunctiva

what is the limbus?

point of transition from cornea to sclera

describe the sclera

opaque, dense irregular connective tissue

the cornea is ________ arrangement and the sclera is _______ arrangement

regular; irregular

what perforates the sclera?

optic nerve at the caudal surface

describe the arrangement of the cornea

Transparent. Composed of layers of regularly- arranged collagen fibers and fibroblasts

is the cornea vascular?

Highly sensitive and Avascular.

describe corneal epithelium

non-keratinized stratified squamous epithelium of anterior surface

describe regeneration of the cornea

Regenerates extremely well from germinal cells in the basal layer of the limbus region

describe Bowmans membrane

a distinctive layer of collagen fibers in the cornea (7 to 12 µm thick)

what is the stroma?

layer of regularly-arranged collagen fibers and keratocytes. The thickest layer of the cornea.

what is the thickest layer of the cornea?

stroma

what is descemets membrane?

a thick (5 to 10 µm) basement membrane underneath the corneal endothelium.

describe corneal endothelium

simple cuboidal epithelium that covers the posterior surface. Functions to keep cornea dehydrated. Does not regenerate

what part of the cornea does not regenerate?

corneal endothelium

if you have a corneal ulcer what membrane was penetrated?

Bowmans membrane

is you penetrate ________ membrane you have a major problem

Descemets

the limbus goes from ________ arranged tissue of the cornea to the _________ arranged tissue of the sclera

regularly; irregularly

what is the sclera covered anteriorly by?

bulbar conjunctiva

________ is continuous with corneal epithelium

conjunctiva

what is the most anterior extension of the choroid?

iris

what does the iris contain?

Contains smooth muscle cells that are radially-arranged (dilator pupillae), or circularly-arranged around the pupil (constrictor pupillae)

describe the ciliary body

Thickening of the choroid at the junction between the posterior 2/3rd and anterior 1/3rd of the eye

what does the ciliary body contain?

ciliary muscle and ciliary processes

what anchor the zonular fibers of the lens?

ciliary body

what is the choroid?

Highly vascular, pigmented layer in the posterior 2/3rd of the eye

the ______ layer is always highly pigmented

vascular

what is the main component of ciliary body?

ciliary muscle

what are the ciliary processes important for?

producing aqueous humor

how is the constrictor papillae arranged around the pupil?

circularly

how is the dilatory papillae arranged?

radially

describe the posterior surface of the uvea

heavily pigmented

describe the anterior surface of the uvea

covered by simple squamous epithelium

describe pars ciliaris retinae

Stratified cuboidal with one pigmented and one non-pigmented layer; part of retina not ciliary body itself

contraction of ciliary muscle causes what?

relaxes zonary fibers

relaxation of ciliary muscles causes what?

tension in zonary fibers

what is the aqueous humor produced by?

epithelium over the ciliary body

where does aqueous humor circulate?

through pupil

where is aqueous humor absorbed?

Absorbed into the vascular channels (canal of Schlemm)

at the iridocorneal angle

describe the choroid

Highly vascular, pigmented layer in the posterior 2/3rd of the eye.

where is the tapetum lucidum located?

A layer that sits between the retina and the choroid. Not found in all species

describe differences seen in some species regarding the tapetum lucidum

• In some species, the tapetum is actually part of the retina.

• Cellular in some species, fibrous in others.

what is the function of the tapetum lucidum?

Reflects light back through the photoreceptor layer to enhance vision in dark environments

where does the retinal pigmented epithelium lack pigment?

over the tapetum lucidum

what covers the inside of the posterior part of the eye?

retina

describe the visual part of the retina (pars optica)

thick, with multiple layers of neurons, and layers between for synapses and nerve fibers to go to the optic nerve

describe the non-visual part of the retina (pars ciliaris and pars iridica)

only two layers, in areas shaded by the iris (the back side of the iris, and over the ciliary body).

what is the point of transition between visual and non-visual regions of the retina?

ora serrata

what are the 10 layers of the optical retina?

1. inner limiting membrane

2. optic nerve fiber layer

3. ganglion cell layers

4. inner plexiform layer

5. inner nuclear layer (bipolar layer)

6. outer plexiform layer

7. outer nuclear layer

8. external limiting membrane

9. photoreceptive layer of rods and cones

10. pigmented epithelium

describe the inner limiting membrane of the optical retina

basement membrane

describe the optic nerve fiber layer of the optical retina

axons of ganglion cells that project into the brain

describe the ganglion cell layer of the optical retina

cell bodies of bipolar neurons

describe the inner plexiform layer of the optical retina

synapses

describe the inner nuclear layer (bipolar layer) of the optical retina

nuclei of various neurons

describe the outer plexiform layer of the optical retina

synapses

describe the nuclear layer of the optical retina

nuclei of rods and cones

describe the external limiting membrane of the optical retina

layer of tight junctions between rods/cones and other neurons.

describe the photoreceptive layer of rods and cones of the optical retina

membrane disks of the rod and cone neurons

describe the pigmented epithelium of the optical retina

simple epithelium that forms the blood-retinal barrier

where do afferent fibers from the retina converge?

optic disc

what creates the blind spot?

Afferent fibers from the retina converge at the optic disc. This creates the blind spot since there are no rods and cones at this spot

in the optic n where does myelinated of the fibers begin?

in the nerve

describe the significance of the optic nerve and retina developing as outgrowths of the brain

meninges surround the optic nerve. The dura is continuous with the sclera

what can increased CSF pressure cause?

bulging around the optic disc

why is the optic nerve considered an extension of the brain?

covered by meninges, and contains CNS glial cells, since it is basically an extension of the brain

what is the fovea?

thinned area in the retina, at the spot where the visual axis meets the retina

what does the fovea allow for?

maximum photoreceptor sensitivity and the greatest visual

discrimination

what is the area around the fovea?

macula

what does macular degeneration affect?

center of visual field

what has the highest concentration of rods and cones?

fovea

what is the lens surrounded by?

capsule

in the lens what do the zonular fibers do?

attach to the capsule around the equator, to suspend it behind the pupil

what is the lens composed of?

fibers derived from the epithelial cells that are on the anterior surface, these cells lose their nuclei and build the lens by adding to the outside

where do zonular fibers radiate from?

the lens capsule to the ciliary process, to suspend the lens

what would occur if the zonular fibers ruptured traumatically or genetically?

prolapse of the lens

describe the anterior surface of the eyelid

covered by skin

in the eyelid describe the cilia near the edge of lids

with associated sebaceous glands, sometimes more prominent in one lid

describe the posterior surface of the eyelid

covered by palpebral conjunctiva which reflects onto the eyeball as bulbar conjunctiva

what is the tarsal plate?

a sheet of dense CT parallel to the bulbar surface, surrounds the Meibomian glands

what is orbicularis oculi?

muscles that close the eyelids located anterior to the tarsal plate

how is the obicularis oculi arranged?

small bundles of skeletal muscle that are arranged circularly around the palpebral fissure

what is bulbar conjunctiva?

covered the visible part of the sclera, and is continuous with the epithelium of the cornea

what is palpebral conjunctiva?

covers the surfaces of the third eyelid, and the inner surface of the eyelid

what is the third eyelid covered with?

palpebral conjunctiva and has a cartilage in the center

how many lymphoid follicles are under the conjunctiva on the surface of the third eyelid facing the eyeball?

3

describe the gland of the third eyelid

surrounds the base of the cartilage, it is lacrimal gland tissue

what is it called when the gland of the third eyelid prolapses?

cherry eye

what contributes to producing the aqueous part of the tears?

-lacrimal gland

-gland of the 3rd eyelid

-deep gland of third eyelid

the tears drain into _______ at the puncta

lacrimal canaliculi