Anatomy of the inner eye

Question 1

Anatomy of the cornea

Answer 1

Makes up the anterior 1/6 of the eye
+/- 500μm at centre
+/- 700μm at periphery
Primary refracting unit of the eye

Question 2

Why are the measurements of the corneal thickness important?

Answer 2

Laser surgery

Question 3

5 layers of the cornea

Answer 3

1. Epithelium
2. Bowman’s membrane
3. Stroma
4. Descemet’s membrane
5. Endothelium

Question 4

Corneal regeneration

Answer 4

Epithelium replaced every 7 days, with new cells formed at the limbus moving from periphery to centre

Question 5

What accounts for 90% of corneal thickness?

Answer 5

Stroma

Question 6

What is the function of corneal endothelium

Answer 6

Hydration of the cornea via active transport and barrier function

Question 7

Reason for the transparency of the cornea?

Answer 7

The uniform spacing of the collagen fibrils in the stroma

any increase in fluid between the fibrils -> corneal cloudiness

Question 8

What is the point of entry for the majority of anterior segment surgery?

Answer 8

The corneoscleral junction (limbus)

Question 9

Trabecular meshwork

Answer 9

90% of aqueous humour outflow from anterior chamber via precisely controlled resistance
Flow can be regulated via cell shape change in response to
- chemicals
- hormones
- neurotransmitters

Question 10

Drainage of aqueous humour

Answer 10

Posterior chamber -> pupil -> anterior chamber -> iridocorneal angle -> trabecular meshwork -> vacuoles -> Schlemm’s canal -> ciliary veins

Question 11

What is the volume of the anterior chamber?

Answer 11

0.2ml

Question 12

What is the volume of the posterior chamber?

Answer 12

0.06ml

Question 13

What is the rate of aqueous humour formation?

Answer 13

+/- 1-2μl per minute

Question 14

How often is the entire volume of aqueous humour replaced?

Answer 14

Every 1-2hrs

Question 15

Functions of aqueous humour

Answer 15

Supplies metabolic needs of avascular lens and cornea
Supports eyeball wall
Maintains eye shape

Question 16

What does the periphery of the iris attach to?

Answer 16

The anterior surface of the ciliary body

Question 17

Why does the iris bulge anteriorly?

Answer 17

Convex anterior surface of lens presses lightly against iris

Question 18

Meaning of mydriasis?

Answer 18

Dilation

Question 19

Meaning of miosis?

Answer 19

Constriction

Question 20

Anatomy of the sphincter pupillae mm

Answer 20

Located in pupillary zone of iris
Allows miosis in 
- bright light
- accomodation
Parasympathetic

Question 21

Anatomy of the dilator pupillae mm

Answer 21

Extends from iris root to sphincter pupillae mm
Allow mydriasis in
- low-intensity light
- during excitement/fear
Sympathetic

Question 22

What is located at the anterior surface of the ciliary body?

Answer 22

Pars plicata

Question 23

What is located at the posterior surface of the ciliary body?

Answer 23

Pars plana

Question 24

Which part of the ciliary body gives rise to the ciliary processes?

Answer 24

Pars plicata

Question 25

Functions of the ciliary body

Answer 25

Lens accommodation

Aqueous humour production

Question 26

Anatomy of the lens

Answer 26

\+/-10mm diameter and 4mm thick in adults
Consists of
- surrounding capsule 
- outer cortex
- inner nucleus

Question 27

Anterior distance of the lens capsule?

Answer 27

20μm

Question 28

Posterior distance of the lens capsule?

Answer 28

3μm

Question 29

Anatomy of the vitreous humour

Answer 29

98% water
Dens gel cortex and more liquid centre
Cortex attached at pars plana and margin of optic disc
With age, gel volume decreases and liquid volume increases

Question 30

Functions of the vitreous humour

Answer 30

Transmit light
Support post surface of lens
Hold neural part of retina to pigmented part of retina
Retinal metabolism

Question 31

Anterior termination of the retina is known as the?

Answer 31

Ora serrata

Question 32

What is the name of the central depression of the macula lutea?

Answer 32

Fovea centralis

Question 33

What is the ora serrata?

Answer 33

The serrated junction between the retina and ciliary body that marks the transition from the simple non-photosensitive area of the ciliary body to the complex multi-layered photosensitive area of the retina

Question 34

Anatomy of the optic disc

Answer 34

Medial to the macula where the optic nerve leaves the retina

Complete rod + cone absence therefore insensitive to light -> “blind spot”

Question 35

Photoreceptos at the fovea central

Answer 35

Rods absent

Cones most dense

Question 36

Anatomy of the macula

Answer 36

+/-5mm in diameter
+/-3mm lateral to optic disc
Yellow colour due to xanthophyll

Question 37

Anatomy of the fovea centralis

Answer 37

Nerve cells and fibres displaced peripherally -> depression

Leaves only photoreceptors in the centre

Question 38

What does the choroid become continuous with at the optic nerve?

Answer 38

Arachnoid mater

Pia mater

Question 39

Functions of the choroid

Answer 39

Nourish outer retinal layers w/ blood vessels
Conduct blood vessels to ant eye regions
Regulates IOP w/ blood flow in the choroidal aa
Absorbs excess light via pigment cells
Allow heat exchange w/ blood vessels

Question 40

What does the sclera fuse with at the optic nerve?

Answer 40

Dura mater

Arachnoid mater

Question 41

Where does the optic nerve penetrate the sclera?

Answer 41

At the lamina cribrosa which also transmits the central aa and vv

Question 42

What causes a cupped disc?

Answer 42

Relatively weak lamina cribrosa may bulge outwards with a rise in IOP

Question 43

Functions of the sclera

Answer 43

Protects the intraocular contents
Preserves eye shape and IOP
Maintains position of ocular structures
Provides rigid insertion for extraocular mm

Question 44

In which population is the sclera bluish?

Answer 44

Infants (underlying choroid showing through thin sclera)

• osteogenesis imperfecta
• iron deficiency anemia

Question 45

Reason for yellow sclera in the elderly?

Answer 45

Fatty deposits

Question 46

Scleral involvement in jaundice?

Answer 46

NO

Bilirubin deposition in the conjunctiva