Ocular Physiology and Histology

Question 1

What are the 4 basic layers of the eye?

Answer 1

Fibrous: cornea & sclara
Vascular: iris, ciliary body, choroid
Neurologic: retina
“other”: lens, aqueous humor, vitreous

Question 2

What are the three major histological divisions of the eye?

Answer 2

anterior segment, posterior chamber, posterior segment

Question 3

What is the name of the junction between the sclara, cornea, and conjunctiva?

Answer 3

the limbus

Question 4

What are the 3 layers of the posterior segment?

Answer 4

outer: sclera
middle: choroid
inner: retina

Question 5

What are the major preretinal factors of vision?

Answer 5

1. refraction and focusing
2. accommodation (ciliary body can change curvature and position of lens)

Question 6

What are the 4 layers of the cornea?

Answer 6

1.epithelium
2. stroma
3. descemets membrane
4. endothelium

Question 7

What are the 4 main functions of the tear fim?

Answer 7

1. bend light
2. protect and nourish ocular surface
3. remove debris and pathogens
4. immune surveillance

Question 8

What are the 3 layers of tear film? functions?

Answer 8

1. lipid layer: prevents evaporation
2. aqueous layer: majority of tear film
3. mucin layer: promotes adherence and spreading on eye

Question 9

What is the difference between the palpebral and bulbar conjunctiva?

Answer 9

palpebral covers inner eyelids
bulbar covers globe up to cornea

Question 10

What is the junction between palpebral and bulbar conjunctiva?

Answer 10

fornix

Question 11

What are the 4 main characteristics of the cornea?

Answer 11

1. avascular: nutrition from aqueous humor and tear film
2. highly ordered for transparency: absorb/scatter UV light, transmit light in visible spectrum
3. thin!: 0.5-0.6mm in dogs and cats
4. highly innervated

Question 12

Why is it difficult to deliver ocular drugs?

Answer 12

1. tear film washes away topical medications
   2.The cornea is meant to function as a barrier
2. Alternating hydrophobic and hydrophilic layers make absorption difficult

Question 13

What are the main components of the corneal stroma

Answer 13

-keratocytes
-ground substance
-collagen fibers

Question 14

Why do the collagen fibers of the corneal stroma have to be precisely arranged?

Answer 14

to limit light scatter

Question 15

Why is descemet’s membrane critical?

Answer 15

it is relatively resistant to degradation by proteases and it is the last line of defense in bad corneal ulcers

Question 16

What critical function does the corneal endothelium perform?

Answer 16

it is involved in the active maintenance of the osmotic gradient between the corneal stroma and aqueous humor

Question 17

How is the lens held in place?

Answer 17

by zonula fibers attaching to the ciliary processes

Question 18

describe epithelial regeneration in the lens

Answer 18

-cells at anterior pole divide and move toward equator
-at equator cells are pushed toward the center of the lens by cells following behind them
-cells elongate and lose organelles
-fibers meet at suture lines

Question 19

What does lens transparency depend on?(3)

Answer 19

precise protein composition
precise spatial arrangement
intact fiber membranes

Question 20

Where does the lens derive its nutrients?

Answer 20

the aqueous humor

Question 21

What disease occures when alterations to the lens proteins or fiber membranes occur?

Answer 21

cataracts

Question 22

What is the vascular/muscular tunic of the eye called?

Answer 22

uvea

Question 23

What are the 6 main functions of the uvea?

Answer 23

1.regulate light entering the eye
2.produces aqueous humor
3.nutritional support, waste removal
4. stabilizes lens
5. helps focus light on retina
6. maintains blood aqueous barrier

Question 24

What are the two structures of the anterior uvea?

Answer 24

-Iris
-Ciliary body

Question 25

What is the structure of the posterior uvea?

Answer 25

choroid

Question 26

What are the main functions of aqueous humor?

Answer 26

-provides glucose, other substances to avascular lens and posterior cornea
-removes metabolites and toxins

Question 27

Where is aqueous humor produced?

Answer 27

the non pigmented ciliary epithelium

Question 28

How is aqueous humor drained from the eye?

Answer 28

-via the conventional outflow pathway: throguh pupil to iridocorneal angle or uveosclaral pathway: absorbed across iris base and out via superchorodial space

Question 29

What is a cause of glaucoma?

Answer 29

changes to aqueous humor drainage pathway

Question 30

What is the function of the choroid?

Answer 30

-metabolic support for the retina
-contains the reflective tapetum

Question 31

What is the retinal pigmented epithelium and its function

Answer 31

technically part of the retina but functionally like the choroid. Its roles are to provide nutrition and oxygen to outer retina, dispose of waste, thermal protection, regeneration of photopigments, part of blood retinal barrier

Question 32

What are the chain of events that leads to light absorption by photoreceptors?

Answer 32

-Na channel closures
-membrane hyperpolarizes
-decrease in glutamate release
(opposite to how neurons work)

Question 33

What are the roles of interneurons in the retina

Answer 33

-increased contrast
-suppression of surrounding photoreceptors
-inhibition or amplification of data

Question 34

Describe the function/pathway of retinal ganglion cells

Answer 34

-receive processed signal from interneurons
-axons from RGC form the optic nerve and run to brain
-# of RGC determines visual acuity

Question 35

What is the name of the exit for the optic nerve?

Answer 35

lamina cribrosa