eyes - anatomy and embryology

Question 1

what embryological structure does the eye develop from?

Answer 1

optic vesicles of the neural tube

Question 2

what is the lens placode?

Answer 2

structure formed from thickening of the surface endoderm when the optic vesicles reach said endoderm

Question 3

what happens when the lens placode starts to invaginate?

Answer 3

the optic vesicle and lens placode forms an optic cup

Question 4

how many layers does the optic cup have?

Answer 4

2

Question 5

what is the choroid fissure?

Answer 5

fissure in the inferior wall of the optic cup which allows blood vessels to pass through said cup

Question 6

what is formed when the choroid fissure doesnt disappear as it normally does?

Answer 6

a gap in tissues develops around it which is called a coloboma

Question 7

what is formed from the surface ectoderm?

Answer 7

eyelids
conjunctiva
corneal epithelium

Question 8

what is formed from the mesenchyme?

Answer 8

choroid
stroma of cornea
sclera and extraocular muscles

Question 9

what forms the lens fibres?

Answer 9

epithelium of lens vesicle

Question 10

what can happen if the walls of the bony orbit fracture?

Answer 10

contents can herniate into surrounding sinuses

Question 11

why is orbital fat important?

Answer 11

it cushions the globe and is key in supporting the contents

Question 12

what forms the fibrous coat of the eye?

Answer 12

cornea
sclera
aqueous humor

Question 13

what forms the vascular coat of the eye?

Answer 13

iris
ciliary body
choroid

Question 14

what forms the sensory coat of the eye?

Answer 14

retina

Question 15

what is the cornea?

Answer 15

the anterior sixth of the eye which is transparent and is a window to allow light rays to enter the eyeball

Question 16

what is the sclera?

Answer 16

the opaque posterior 5/6 of the eye which gives attachment to the muscles moving the eyeball

Question 17

what type of epithelium is present in the cornea?

Answer 17

stratified squamous non keratinised?

Question 18

what is bowmans membrane?

Answer 18

basement membrane of corneal epithelium

Question 19

what is the stroma of the cornea?

Answer 19

regularly arranged collagen - no blood vessels

Question 20

what lies between the stroma of the cornea and the endothelium of the cornea?

Answer 20

descemets layer

Question 21

how is opacification of the cornea treated?

Answer 21

corneal transplant - keratoplasty

Question 22

what are the 2 broad types of cornea pathology?

Answer 22

inflammatory - eg corneal ulcer

non inflammatory - dystrophies

Question 23

how is the avascularity of the cornea a benefit during surgery?

Answer 23

less chance of grafts being recognised by the recipient so less chance of a rejection

Question 24

what is the purpose of the ciliary body?

Answer 24

suspends the lens and produces aqueous humor

Question 25

what is the purpose of the choroid?

Answer 25

supplies blood to the outer layers of the retina

Question 26

what is the function of the iris?

Answer 26

controls the diameter of the pupil and thereby controls the amount of light rays entering the eyeball

Question 27

what are the 10 layers of the retina?

Answer 27

``` pigment epithelial layer layer of rods and cones outer limiting membrane outer nuclear layer outer plexiform layer inner nuclear layer inner plexiform later ganglion cell layer nerve fibre layer inner limiting membrane ```

Question 28

what is the clinical term for lens opacification?

Answer 28

cataract

Question 29

where is the anterior segment of the eye?

Answer 29

in front of the lens

Question 30

where is the posterior segment of the eye?

Answer 30

behind the lens

Question 31

where is the anterior chamber of the eye?

Answer 31

in front of the iris

Question 32

where is the posterior chamber of the eye?

Answer 32

behind the iris

Question 33

what is the aqueous humor?

Answer 33

watery fluid anterior to the lens - it helps maintain intraocular pressure

Question 34

what is the vitreous humor?

Answer 34

transparent gel posterior to the lens - it helps cushion the retina

Question 35

what is aqueous humor produced by?

Answer 35

ciliary body

Question 36

what filters aqueous humor out of the anterior chamber?

Answer 36

trabecular meshwork

Question 37

what happens if the pathway of the circulation of the aqueous humor is obstructed?

Answer 37

increase in intraocular pressure which leads to glaucoma

Question 38

what are the conjunctiva?

Answer 38

thin vascular membrane that covers the inner surface of the eyelids and loops back over the sclera

Question 39

does the conjunctiva cover the cornea?

Answer 39

no

Question 40

where is the lacrimal gland situated?

Answer 40

in the orbit laterally

Question 41

what innervates the lacrimal gland?

Answer 41

facial nerve

Question 42

where do the lacrimal ducts open into?

Answer 42

conjunctival sac

Question 43

what happens in regards to lacrimal secretions when we blink?

Answer 43

eyelids spread tears evenly on the thin surface of the cornea

Question 44

where do tears drain?

Answer 44

through punctae on the medial side of each eyelid and then to the lacrimal sac

Question 45

where is the lacrimal sac situated?

Answer 45

over the lacrimal bone

Question 46

where does the lacrimal sac drain to?

Answer 46

to the inferior meatus of the nasal cavity through the nasolacriminal duct

Question 47

what are the functions of the tear film?

Answer 47

1. keeps cornea moist 2. washes away any particulate foreign bodies 3. has antibodies and lysozymes to kill microbes 4. smoothes outer surface of the cornea providing smooth surface for refraction

Question 48

what are the 3 layers of the tear film?

Answer 48

mucinous layer aqueous layer oily layer