Anatomy and Embryology of the Eye

Question 1

where do the optic vesicles grow outwards from?

Answer 1

diencephalic part of neural tube towards surface ectoderm

Question 2

what occurs once the optic vesicles reach the surface ectoderm?

Answer 2

cause some of the cells on this surface ectoderm to thicken forming the lens placode

Question 3

what happens after the lens placode is formed?

Answer 3

The lens placode starts to push inwards (invaginate), which causes the optic vesicle too, to form an optic cup

Question 4

how many layers of the optic cup initially form?

Answer 4

2 layered optic cup

Question 5

what is the fissure that allows blood vessels to pass through inferior optic cup wall?

Answer 5

choroid fissure

Question 6

what ultimately happens to the lens vesicle?

Answer 6

looses its connection with the surface ectoderm

Question 7

what does the surface ectoderm form?

Answer 7

eyelids, conjunctiva, corneal epithelium

Question 8

what does the mesenchyme form?

Answer 8

choroid, stroma of cornea, sclera and extraocular muscles

Question 9

what does the outer layer of the optic cup form?

Answer 9

pigment layer of retina and iris

Question 10

what does the inner layer of the optic cup form?

Answer 10

neural layer of retina, ciliary body and inner layer of iris

Question 11

what forms the lens fibres?

Answer 11

epithelium of lens vesicle & later loose their nucleii.

Question 12

how does retinal detachment usually occur?

Answer 12

Tends to happen when fluid gets into potential space between inner 9 layers of retina and 10th outer layer
Can occur following trauma

Question 13

what occurs if the choroid fissure persists?

Answer 13

forms a gap in tissues which develop around it . This gap is called a Coloboma

Question 14

where can coloboma occur?

Answer 14

iris-keyhole pupil
retina
only disc

Question 15

what are strongest parts of the orbit?

Answer 15

orbital rims and lateral and superior walls

rest easily fractured

Question 16

what can orbital floor fracture lead to?

Answer 16

herniation into maxillary sinus

Question 17

what are common symptoms of an orbital floor fracture?

Answer 17

Restricted vertical movement of the eye
Subconjunctival hemorrhage
Swollen lid
Loss of sensation over upper cheek area

Question 18

what eye sign can thyroid disease lead to?

Answer 18

Orbital fat hypertrophies leading to the staring appearance

Question 19

describe the epithelium of the cornea

Answer 19

stratified squamous non-keratinised.

Question 20

why is the cornea transparent?

Answer 20

Histologically – regular arrangement of collagen in stroma
No blood vessels
Endothelium cell layer has a pump that actively keeps the aqueous humor out.

Question 21

give an example of an inflammatory/no inflammatory disease of the cornea

Answer 21

Inflammatory – corneal ulcers

Non-inflammatory – dystrophies

Question 22

what do corneal pathologies frequently lead to?

Answer 22

opacification of the cornea. This might need to be treated by corneal transplant - Keratoplasty

Question 23

why is the avascularity of the cornea such a benefit to surgeons?

Answer 23

a lesser chance of foreign antigens from a corneal graft being recognised by the recipient

Question 24

what is the choroid made up of?

Answer 24

fenestrated blood vessels of varying diameter. These supply the outer layers of the retina with blood by diffusion

Question 25

in the retina are the nerve fibres above or below the cones and rods?

Answer 25

(except for fovea)
nerve fibres above (9th layer)
layer of rods and cone below (2nd layer)

Question 26

what is the layer that absorbs all the extra light, underneath the layer of rods and cones?

Answer 26

Pigment epithelial layer

Question 27

how does the fovea centralis differ from the rest of the retina?

Answer 27

packed with cones, so maximum visual acuity

layers have been pushed to side bringing rods & cones up to the surface

Question 28

what is the lens?

Answer 28

Transparent, crystalline biconvex structure which is suspended by zonules from the ciliary body. It can change shape (i.e. become less or more convex.)

Question 29

how is the lens transparent?

Answer 29

it needs to be avascular

predisposes it to become opaque later in life

Question 30

what is lens opacification called?

Answer 30

cataract

Question 31

what is the aqueous humor and what is its role?

Answer 31

watery fluid anterior to the lens.It helps maintain intraocular pressure.
constantly circulating fluid that also nourishes the lens and the cornea.

Question 32

what is the vitreous humor and what is its role?

Answer 32

transparent gel posterior to the lens.It helps cushion the retina.

Question 33

where is the aqueous humor produced?

Answer 33

ciliary body, in the space behind the iris and in front of the lens (the posterior chamber - PC)

Question 34

once inside the anterior chamber where does the aqueous humor go?

Answer 34

reaches the angle of the AC where it gets filtered out through a meshwork called the trabecular meshwork

Question 35

at the meshwork where does the aqueous humor go through?

Answer 35

Schlemm’s canal

Question 36

what does an obstruction along the pathway of circulation of aqueous humor lead to?

Answer 36

damming up of AH-increased intraocular pressure- GLAUCOMA

Question 37

where do the lacrimal gland ducts open into?

Answer 37

conjunctival sac

During each blink, eyelids spread tears evenly on the surface of cornea

Question 38

where are the tears drained into?

Answer 38

drains into lacrimal sac

Then drains through nasolacrimal duct into the inferior meatus of the nasal cavity.

Question 39

what is the function of tears?

Answer 39

keeps cornea moist , prevents drying
Washes away any particulate foreign bodies
Has antibodies and lysozymes -kills microbes
providing smooth surface of cornea for refraction.

Question 40

what nerve leads to secretion of tears?

Answer 40

Parasympathetic (VII n)

Question 41

what are the three layers of the tear film?

Answer 41

mucinous layer
aqueous layer
oily layer-most superficial

Question 42

what stimulates further blinking?

Answer 42

When eyelids are open, aqueous component of tears evaporates, and when oily layer touches mucin layer, tear film breaks up