Anatomy and physiology of the eye orbit

Question 1

what are the 5 components that make up the orbit and its contents

Answer 1

1. bony orbit
2. contents including fat
3. eyeball
4. eyelid (and lacrimal ducts)
5. muscles

Question 2

what makes up the fibrous coat of the eyeball

Answer 2

the sclera and cornea

Question 3

what makes up the vascular coat of the eyeball

Answer 3

the iris, ciliary body and choroid

Question 4

what makes up the sensory coat of the eyeball

Answer 4

the retina (+optic nerve)

Question 5

what sits between the cornea and the lens in the anterior segment

Answer 5

aqueous humour

Question 6

what sits behind the lens in the anterior segment

Answer 6

vitreous humour

Question 7

what sort of epithelium does the cornea have

Answer 7

stratified squamous non-keratinised

Question 8

what are the different histological layers of the cornea going from the outside to the aqueous humour

Answer 8

1. epithelium
2. bowmans membrane (basement membrane of corneal epithelium)
3. stroma - regularly arranged collagen, NO blood vessels
4. descemets layer
5. endothelium - single layer

Question 9

what 3 things allow for the transparency of the cornea to be maintained

Answer 9

1. histologically - regular arrangement of collagen in stroma
2. NO BLOOD VESSELS
3. endothelium cell layer has a pump that actively keeps aqueous humour out

Question 10

why is the cornea believed to be an “immune-privileged” site

Answer 10

due to no blood vessels, when performing corneal transplants there is a lesser chance of foreign antigens from a graft being recognised by the recipient - less chance of graft rejection

Question 11

what comprises the ciliary body of the eye

Answer 11

ciliary muscles (control the shape of the lens)
ciliary epithelium (produce aqueous humour)

Question 12

what is the trabecular meshwork and where is it located

Answer 12

located around the base of the cornea near the ciliary body - drains aqueous humour from the eye via the anterior chamber

Question 13

where does the trabecular meshwork drain the aqueous humour to

Answer 13

schlemms canal - fluid drains into this set of tubes that flow into the blood stream

Question 14

what is the choroid of the eye

Answer 14

vascular layer of the eye made from fenestrated blood vessels of varying diameter - supply outer layers of the retina with blood by diffusion

Question 15

where is the choroid located

Answer 15

lies between retina and sclera

Question 16

where do the outer layers of the retina get their blood supply from

Answer 16

choroid - by diffusion

Question 17

where do the inner layers of the retina get their blood supply from

Answer 17

central retinal artery

Question 18

what are the 10 layers of the retina (from choroid to vitreous humour)

Answer 18

1. pigment epithelial layer
2. receptor layer (layer of rods and cones)
3. outer limiting membrane
4. outer nuclear layer
5. outer plexiform layer
6. inner nuclear layer
7. inner plexiform layer
8. ganglion cell layer
9. nerve fiber layer
10. inner limiting membrane

Question 19

what is the macula of the eye

Answer 19

area responsible for sharp, detailed, central vision

Question 20

what is the fovea centralis

Answer 20

located in the centre of the macula - contains a very high concentration of cones = MAXIMUM ACUITY

Question 21

what is the structure of the lens of the eye

Answer 21

transparent, crystalline bionvex structure - suspended by zones from the ciliary body - can change shape to become more or less convex

Question 22

why is the lens transparent

Answer 22

it is avascular

Question 23

what does vascularity of the lens predispose it to in later life

Answer 23

lens opacification - cataract

Question 24

what are the three layers of the tear film

Answer 24

1. mucinous layer (~30%) - overlying corneal epithelium
2. aqueous layer (~69% - )over mutinous layer
3. oily layer (<1%) - most superficial layer

Question 25

what are the 4 functions of the tear film

Answer 25

1. keeps cornea moist- prevents drying 2. washes away particular foreign bodies 3. antibodies and lysosomes to kill microbes 4. smooths outer surface of cornea providing smooth surface for refraction

Question 26

what causes secretion of tears into conjunctival sac

Answer 26

parasympathetic stimulation of facial (VII) nerve

Question 27

what happens to the tear film during a blink

Answer 27

sharp lower border of the upper eyelid evenly distributes tear film over eye

Question 28

how is blinking stimulated

Answer 28

when eyelids open aqueous component of tears being to evaporate - oily layer an much layer come close together - when these two layers touch each other the teat film breaks up and stimulates blinking

Question 29

embryologically where do the optic vesicles grow from

Answer 29

grow outwards from diencephalic part of neural tube towards ectoderm surface

Question 30

what is the role of the cornea

Answer 30

transparent window to allow light rays to enter the body

Question 31

what is the role of the sclera

Answer 31

gives attachment to muscles moving the eyeball

Question 32

what is the role of the ciliary body

Answer 32

suspends the lens and produces aqueous humour

Question 33

what is the role of the choroid

Answer 33

supplies blood to outer layers of retina

Question 34

what is the role of the iris iris

Answer 34

controls diameter of pupil and thereby control how much light enters

Question 35

what is the role of the retina

Answer 35

contains light sensitive rods and cones which enable us to see

Question 36

what is the aqueous humour

Answer 36

watery fluid that helps maintain intraoccular pressure

Question 37

what is the vitreous humour

Answer 37

transparent gel that helps cushion the retina

Question 38

what is the role of orbital fat

Answer 38

cushions the globe in the orbit

Question 39

what are the components of the eyelids

Answer 39

skin on the outside - mucous membrane on the inside (conjunctivae) eyelashes with sebaceous glands muscles to elevate and close eyelids hard plate to keep shape (tarsal plate) oily secretory glands (to create the tear film)

Question 40

what is the conjunctiva

Answer 40

thin vascular membrane that covers the inner surface of the eyelids and loops back over the sclera DOES NOT cover cornea

Question 41

what does the lacrimal gland do

Answer 41

secretes tears that are spread over the surface of the corner with each blink

Question 42

where does the tear film drain

Answer 42

lacrimal duct

Question 43

what is the arterial supply of the orbit

Answer 43

ophthalmic artery

Question 44

what arteries supply the anterior choroid, ciliary bodies and iris

Answer 44

long posterior ciliary arteries

Question 45

what veins drain the orbit

Answer 45

superior and inferior ophthalmic veins - drain to the cavernous sinus

Question 46

what happens when the optic vesicles reach the surface ectoderm

Answer 46

cells of the surface ectoderm thicken - create the lens placode

Question 47

how is the embryological optic cup formed

Answer 47

the lens placode pushes inwards which causes the optic vesicle to do so as well forming a 2 layered optic cup

Question 48

how is the choroid fissure formed

Answer 48

as the optic cup is forming, blood vessels that pass through form a fissure in its anterior wall = choroid fissure

Question 49

what does the surface ectoderm go to form

Answer 49

eyelids, conjunctivae, corneal epithelium

Question 50

what is the mesenchyme derived from

Answer 50

mesoderm and neural crest cells

Question 51

what does the mesenchyme form

Answer 51

choroid, storm of cornea, sclera and extraocular muscles

Question 52

what are lens fibres formed from

Answer 52

epithelium of the lens vesicle