Lecture 21 Histology of the Eye

Question 1

Name the three tunics of the eyeball

Answer 1

Fibrous Tunic
Vascular Tunic
Inner Tunic

Question 2

Fibrous Tunic

Answer 2

Sclera (tunica fibrosa)

Cornea

Question 3

Vascular Tunic

Answer 3

Choroid
Ciliary Body
Iris

Question 4

Inner Tunic

Answer 4

Retina

Question 5

Sclera Layers

Answer 5

Episcleral Layer
Sclera Proper
Lamina Cribrosa

Question 6

Episcleral layer

Answer 6

Outer layer
Loosely arranged collagen and elastic fibers
Highly vascular
Attaches the lining of the eyelid (conjunctiva) to the sclera

Question 7

Sclera Proper

Answer 7

Made up of interlacing collagen fibers
Attachment site for tendons or extrinsic eye muscles
Collagen bundles are always parallel to outer surface of sclera

Question 8

Lamina Cribrosa

Answer 8

Perforated disc of sclera

Pass through for optic nerve fibers

Question 9

What is the name of the junction between the sclera and the cornea? What is its characteristic?

Answer 9

The Limbus

It is highly vascularized

Question 10

Name the layers of the cornea

Answer 10

Corneal epithelium 
Bowman's membrane 
Corneal stroma 
Descemet's membrane 
Corneal Endothelium

Question 11

Corneal Epithelium

Answer 11

Stratified, nonkeratinized squamous epithelium (5-6 layers)

High mitotic activity in the basal layer (Turnover = 1 week)

Question 12

Bowman’s membrane

Answer 12

Acellular layer separated epithelium from stroma

Randomly arranged collagen fibers

Question 13

Corneal Stroma

Answer 13

Thin layers of ordered arrays of collagen fibers

Question 14

Descement’s membrane

Answer 14

Acellular layer of collagen bundles

Separates stroma from endothelium

Question 15

Corneal endothelium

Answer 15

Single layer of large squamous cells

Question 16

Choroid (Part of the Vascular Tunic)

Answer 16

Extends anterior to ora serrata of the retina
Highly vascularized with loose CT
Bruch’s (glassy) membrane

Question 17

Describe the highly vascularized loose connective tissue of the choroid

Answer 17

Forms choriocapillary network - contains small BVs that supply cells of the retina
Provides nutrients to outer layers of the retina
Consists of medium & large arteries & veins as well as a wide-bore capillary network
Contains melanocytes

Question 18

Describe Bruch’s (glassy) membrane of the choroid

Answer 18

Acellular fused basal laminae of choriocapillaries and pigmented retinal epithelium

Question 19

Ciliary body (Part of the Vascular Tunic)

Answer 19

Wedge-shaped expansion of choroid peripheral to the lens
Covered by a double layer of cells
Suspensory ligaments (of Zinn) extend to just behind lens equator and anchor the lens in place
Ciliary muscles

Question 20

Describe the double layer of cells in the ciliary body

Answer 20

Innermost layer is continuous with the pigmented layer of the retina
Surface layer is from the sensory layer of the retina
Produces aqueous humor

Question 21

Describe the ciliary muscles of the ciliary body

Answer 21

Smooth muscle mass that changes the shape of the lens

Innervated by parasympathetic neurons

Question 22

Ciliary muscles and accommodation:

Answer 22

One group of muscles is responsible for flattening the lens

A second group of muscles is responsible for allowing the lens to become thicker

Question 23

Describe the nonpigmented surface layer of cells of the ciliary body

Answer 23

Produce aqueous humor
Basal infoldings
Secrete aqueous humor into posterior chamber

Question 24

Aqueous humor

Answer 24

Percolates through trabecular mashwork

Flows into canal of Schlemm

Question 25

Iris (Part of the Vascular Tunic)

Answer 25

Located anterior to the lens and separates the anterior and posterior chambers
Angle
Surround Pupil
Double layer of epithelium
Melanocytes - the more melanocytes, the darker

Question 26

Describe the Angle of the Iris

Answer 26

Formed at lateral borders of the anterior chamber
Loos CT
Part of the passageway of aqueous humor

Question 27

Describe the double layer of epithelium of the Iris

Answer 27

Inner layer = pigmented epithelial cells
Outer layer of radially oriented myofilaments - dilator pupillae muscle, sympathetic innervation, dilate pupil
Concentric layer of myofilaments - constricts pupil, parasympathetic innervation

Question 28

What are the two subdivisions of the retina?

Answer 28

Photosensitive region that lies posterior to the ora serrata

Non-photosensitive region that lies anterior to the ora serrata

Question 29

Describe the photosensitive region of the retina

Answer 29

Optic Disc

Fovea Centralis

Question 30

Optic disc of photosensitive region of retina

Answer 30

Region on posterior aspect of eye where optic nerve exits

Has no photosensitive retina & constitutes the blind spot

Question 31

Fovea centralis of photosensitive region of retina

Answer 31

About 2.5 mm lateral to optic disc
Contains yellow pigment = macula lutea
Contains only cone-type photoreceptors
Area of most acute vision

Question 32

Describe the non-photosensitive region of the retina

Answer 32

Consists of two cell layers covering iris, ciliary body, and ciliary processes

Question 33

What are the chambers of the eye?

Answer 33

Anterior chamber
Posterior chamber
Vitreal chamber

Question 34

Anterior chamber

Answer 34

Posterior to cornea and anterior to iris

Question 35

Posterior Chamber

Answer 35

Posterior to iris and anterior to lens

Question 36

Vitreal Chamber

Answer 36

Posterior to lens
Contains vitreous body
Gelatinous mass made up of 99% water, hyaluronic acid, and vitrein
Hyaloid canal is the site of fetal artery

Question 37

Glaucoma

Answer 37

Increased intraocular pressure due to compromised drainage of aqueous humor from anterior chamber