Development And Histology Of The Eye

Question 1

What makes up the fibrous tunic of the eye?

Answer 1

Sclera and cornea

Question 2

What structures make up the vascular tunic (urea) of the eye?

Answer 2

Choroid

Ciliary body

Iris

iris and ciliary body also kinda cross into the retina layer

Question 3

What structures make up the retina (internal layer) of the eye?

Answer 3

Visual retina

Non-visual retina

• iris
• ciliary body

Question 4

When does development of the eye start?

Answer 4

Week 3 (approx 22 days)

Developers from the optic groove

• is part of the neural ridge that invaginates into the neural tube.
• is neural ectoderm derived

Once the optic groove invaginates far enough (close to the surface ectoderm) a part of the surface ectoderm becomes thickened and turns into the optic vesicle
- this is around week 4

When the optic vesicle is produced and the optic groove gets closer, the optic cup is formed
- this is made up of the optic vesicle and the lens vesicle (this forms the eye itself)

Question 5

What artery and veins supply the optic cups and placode during development?

Answer 5

Hyaloid artery/vein

- helps become optic nerve and blood supply of the adult

Question 6

Coloboma

Answer 6

Incomplete closure of the retinal fissure that results in a ventral defect in the retinal layer

Question 7

Congenital aniridia

Answer 7

Failure of the iris to develop

Can be due to either

• failure of the optic rim to grow around lens
• inadequate migration of the iridium tissues

Question 8

Congenital detached retina

Answer 8

Caused when the neural and pigment retinal layers do not adhere properly

common with downs and Marfan syndrome patients

Question 9

Congenital aphakia

Answer 9

Failure of the lens to develop via either lens placode not forming or failing to undergo induction of the lens vesicle

Question 10

What are the 5 layers of the cornea

Answer 10

From external -> internal

1) external epithelium (cornea epithelium)
- non-keratinized squamous epithelium
* very highly innervated since it has reflexes*

2) bowmans membrane
- basement membranes for external epithelium
* does not regenerate, only scars*

3) Stroma
- collagen fibers that are perpendicular

4) Descetes membrane
- basement membrane of stroma layer

5) internal endothelium
- maintains hydration of the cornea
* damage leads to swelling of the cornea*

Question 11

How does lens accommodation work mechanically?

Answer 11

Relaxed

• ciliary muscles are relaxed and pull on zonule fibers
• zonule fibers are taut and flatten the lens which causes focusing on distant objects
• least amount of refraction
• low parasympathetic activity

Focused

• ciliary muscle contracts and relaxes the zonule fibers
• zonule fibers are relaxed and round the lens to focus on closer objects
• most amount of refraction
• high parasympathetic activity

Question 12

Myopia (nearsighted)

Answer 12

Often due to the eye being “too long”

Results in the focal plane to be in front of the retina. Also causes too much light refraction or the lens being too curved

See close objects fine, difficulty adjusting to far away objects

Question 13

Hyperopia (farsightedness)

Answer 13

Often due to the eye being “too short”

Results in the focal plane to be placed behind the retina and causes very little light refraction

Cornea and lens are too flat

See far objects fine, difficulty adjusting to up close objects

Question 14

Astigmatism

Answer 14

Myopia or hyperopia due to refractive errors

- the shape of the cornea or lens is curved more steeply in one direction

Question 15

Pigmented vs non-pigmented epithelium of the ciliary body

Answer 15

Non-pigmented = continuous with outer pigmented layer of visual retina

Pigmented = continues with inner neural layer of the visual retina
- specifically produces aqueous humor into the posterior chamber

Question 16

Cataracts

Answer 16

Formation of the opaque regions of the lens grow too much and obstruct the passage fo light to the retina

Question 17

Glaucoma

Answer 17

Excessive accumulation of aqueous humor causes increased internal pressure of the eye

Damages the cornea and/or retina overtime

Question 18

Mydraisia vs miosis

Answer 18

Mydriasia = excessive pupil dilation
- caused by loss of parasympathetic activity

Miosis = excessive pupil constriction
- caused by loss of sympathetic activity

Question 19

Photoreceptor neurons

Answer 19

Primary sensory Afferent neurons that take light energy and transfer them into neuronal signals to visual cortex

Rods = react to light intensity (night vision and motion)
- contain primarily rhodopsin proteins

Cones = react to light wavelength (color)
- contains primarily iodopsin proteins

Question 20

Conducting neurons

Answer 20

Conducts nerve impulses from one neuron to another.

Bipolar = secondary sensory afferents that relay neural signals form the photoreceptors to the ganglion cells

Ganglion = tertiary sensory afferent neurons that relay neural signals from bipolar neurons to related visual nuclei isn’t he brain via the optic nerve

Question 21

Two types of support cells for the retina

Answer 21

Muller cells

Astrocytes

Question 22

Where do rods and cones get blood and nutrients from?

Answer 22

Choroid also vascular supplies