L7 & L8 - Vision I and II

Question 1

The three layers of the eyeball

Answer 1

Outer tunic - contains cornea/sclera, is fibrous

Middle tunic - consists of choroid, ciliary body, and iris, and is vascular and pigmented, also called (uveal tract)

Inner tunic - consists of the retina, is neurosensory

Question 2

Outer tunic: what amount do the cornea and sclera take up, and what are its key characteristics?

Answer 2

Cornea - anterior/superficial 1/6th
Sclera - posterior/deep 5/6ths

• Transparent
• Avascular

Question 3

Cornea: what does it do, what features help it do these purposes, what key features does it have, and what can incorrect shaping lead to?

Answer 3

Refract light - curvature of the anterior corneal surface, tear film (moist), and corneal thickness
Transmit light - regularly arranged epithelium

Avascular (oxygen is supplied from the tear film by dissolving and the aqueous humor supplies it with nutrients)

Incorrect shaping - astigmatism

Question 4

Sclera: what is it made from, what does it do, and what features help it do its function?

Answer 4

Tough collagen fibres

Provides rigidity - allows insertion of extraocular muscles which help maintain eyeball shape

It is also opaque - the whites of the eye

Question 5

What is the name of the place where the cornea meets the sclera?

Answer 5

The limbus

Question 6

Cornea histology anteriorly-posteriorly/superificial-deep

Answer 6

Epithelium - stratified squamous, cells always getting damaged so must be replaced quickly

Bowman’s layer - acellular, composed of collagen fibres, function is debatable (removal doesn’t lead to functional issues, maybe rigidity?)

Stroma - thickest layer, parallel collagen fibre layers allow transparency

Descemet’s membrane - acellular, composed of collagen fibres, function is debatable (removal doesn’t lead to functional issues, maybe rigidity?)

Endothelium - simple cuboidal epithelia, in contact with the aqueous humour

Question 7

Sclera histology anteriorly to posteriorly

Answer 7

Fascial sheath - the hammock of the eyeball, connective tissue that the eyeball sits in

Episclera - tough connective tissue layer

Stroma - same as cornea except fibres are randomly arranged, meaning it’s opaque

Lamina fusca - thin pigmented tissue layer

Choroid - Large part of the middle tunic, not part of the sclera really

Question 8

What is another word for stroma?

Answer 8

Connective tissue

Question 9

Aqueous humor

Answer 9

Transparent liquid lying anteriorly to the pupil and posterior to the cornea

It gives nutrients to the cornea

Question 10

Scleral perforations

Answer 10

Anterior - anterior ciliary vessels, recti muscles

Posterior - optic nerve, central retinal vessels, ciliary nerves and vessels

Central - vortex veins

Lamina Cribrosa - the weakest part of the sclera, surrounds the optic nerve (sieve type beat, allows things to leave the eye)

Question 11

Recti muscles

Answer 11

extraocular muscles

Question 12

Middle tunic

Answer 12

Choroid - ciliary body - iris

Choroid - vascular pigmented layer, allows the passage of blood vessels and nerves to the anterior part of the eye, and prevents unwanted reflection of light

Ciliary body - accommodation, produces and secretes aqueous humor, and suspends the lens

Iris - controls pupil diameter

Question 13

Choroid histology anteriorly to posteriorly

Answer 13

Passes from the back of the eye to the ciliary body, a large part of the middle tunic and immediately deep to the sclera

Suprachoroid - transition zone

Stroma - contains blood vessels, connective tissue, and melanocytes

Choriocapillaris - the deepest layer of vessels, supply blood to the retina

Bruch’s membrane - multi-layered sheet with an elastic core

Question 14

Accommodation: what is it, how does the lens differ in different scenarios, and what allows accommodation to happen?

Answer 14

Changing the lens to change the view target (close object vs far object)

When looking at close objects - the lens is globular
When looking at far objects - the lens is thin

Lens accommodation occurs by the ciliary body

Question 15

Melanocytes: what are they and what do they do?

Answer 15

Melanin pigment that absorbs excess light, and prevents unwanted reflection

Question 16

Ciliary body histology

Answer 16

Ciliary muscle - three sets of smooth muscle fibres (these allow accommodation to occur)

Ciliary stroma - vascular connective tissue, enters into finger-like processes - ciliary processes (this region where ciliary processes are called pars plicata)

Ciliary epithelium - double layer, the outer is pigmented, the inner is non-pigmented, and it produces and secretes aqueous humour (outer-faces retina, inner faces ciliary stroma)

In accommodation for a close object, the ciliary body moves forward (contracts towards the lens) - suspensory ligaments become slack, allowing the lens to go globular and focus on something closer to the face

Question 17

Pars plicata

Answer 17

The part of the ciliary body where you have all the ciliary processes

Question 18

Iris histology

Answer 18

Stroma - contains sphincter pupillae muscle (innervated by parasympathetic NS)

Double epithelium layer - anterior myoepithelial layer containing the dilator pupillae muscle (innervated by sympathetic NS)

Question 19

Miosis

Answer 19

Constriction/narrowing if the eye pupil using the sphincter pupillae muscle

Occurs when the parasympathetic nervous system is activated

Question 20

Mydriasis

Answer 20

Dilation/enlargement of the eye pupil using the dilator pupillae muscle

Occurs when the sympathetic nervous system is activated

Question 21

Collarette

Answer 21

Thick part of the iris, thick collagen layer surrounding the pupil

Part of the ciliary zone

Question 22

Trabeculae

Answer 22

Columns of collagen that radiate from the pupil

Part of the ciliary zone

Question 23

Fushs’ crypts

Answer 23

The part between trabeculae

Ciliary zone

Question 24

Inner tunic

Answer 24

Retina - transforms light energy into a neural signal

Question 25

Retina histology superficial to deep

Answer 25

Ganglion cells - nerves that transmit visual information towards the optic nerve Amacrine cells - found at the interface between ganglion cells and bipolar cells Bipolar cells - two poles (the only other place bipolar cells are found is in the ears) Horizontal cells - found at the interface of photoreceptors and bipolar cells, reach across several cells allowing for horizontal processing and allows for fine-tuning of receptive information for sharp images Photoreceptors - rods/cones Pigmented epithelial layer - take photoreceptors that have had their shape altered after being hit by light and repackaging them and putting them back in their layer

Question 26

Photoreceptors

Answer 26

Rods/cones When light hits the photopigment discs, they get damaged and move towards the epithelium later where it is repackaged and moved back to the layer

Question 27

In what direction is light transmitted/received?

Answer 27

Light enters towards the epithelial layer, information is moved in the opposite direction towards the ganglion

Question 28

Retinal layers superficial to deep and the parts of the retina they are associated with

Answer 28

A layer of optic nerve fibres Inner limiting membrane - muller cells, help with retinal structure Ganglion cell layer Inner plexiform layer - axons of horizontal, amacrine, and bipolar cells Inner nuclear layer - horizontal, amacrine, and bipolar cells' nuclei Outer plexiform layer - processes of rods and cones Outer nuclear layer - nuclei of rods and cones Outer limiting membrane - muller cells, help with retinal structure Layer of rods and cones Retinal pigment epithelium Choroid - not an actual part of the retina so retina has 10 different layers (remember that at the back of the eye, where light is focussed onto, the layers go inner-middle-outer)

Question 29

'Processes' what do they really mean?

Answer 29

Processes are essentially the axon of things that aren't neurones

Question 30

Horizontal cells: what type of information do they transfer, what do they do, and how many types are there?

Answer 30

Horizontal transfer of information Able to effect inhibitory response Several different types

Question 31

Amacrine cells: what type of information do they transfer and what do they do?

Answer 31

Horizontal transfer of information Modulates information reaching ganglion cells

Question 32

Bipolar cells: what type of cells are they, what do they do, and how many types are there?

Answer 32

1st-order neurones of the visual pathway relay information from photoreceptors to ganglion cells Many different types

Question 33

Ganglion cells: what type of cells are they, where do their axons form, how do they leave the eye, and how many types are there?

Answer 33

2nd order neurones of the visual pathway Axons form the optic nerve Exit the retina at the optic disc - optic nerve exists eyeball at lamina cribrodsas Many different types

Question 34

Retinal pigmented epithelium: what is it, what are its functions, and what are its anatomical relations?

Answer 34

Pigmented epithelial layer that forms the last layer of the retina * Protection (forms part of blood-retina barrier) * Phagocytoses fragments from the photoreceptor outer layer * Metabolises and stores vitamin A * Produces growth factors * Pigment helps to decrease the excess scattering of light Directly superficial to Brush's membrane and directly deep to the outer segment of the photoreceptors

Question 35

Ophthalmoscope view of the eye

Answer 35

Yellow spot - optic disc Lateral to yellow spot, dark red spot - macula lutea, fovea centralis centrally

Question 36

Fovea centralis: what does it have the body's highest concentration of?

Answer 36

Cones, colour detection stuff

Question 37

Clivus

Answer 37

The parts that rise up out of the foveola, but is still part of the fovea

Question 38

Aqueous humour: what does it do and what does it contain?

Answer 38

Supplies metabolic needs of the eye's avascular structures (lens/cornea) Supports the wall of the eyeball and helps to maintain its shape * Water * Glucose * Proteins * Dissolves gasses * Other nutrients

Question 39

Vitrous humour: what does it do and what does it contain?

Answer 39

Helps maintain eyeball shape Transmits light Contributes to the dioptric power of the eye Support lens Supports retinal layers * Proteins * Salts * Acids * Hyalocytes * 98% water

Question 40

Hyalocytes

Answer 40

Cell types that clump together and give you floaters

Question 41

Eyeball segments/chambers: how is an anatomical position determined?

Answer 41

The lens determines the anteriority/posteriority of SEGMENTS chambers are ONLY found in the anterior segment - the anterior chamber is between the iris and cornea and the posterior chamber is behind the pupil, in front of the lens

Question 42

Label the following: - Lens - Iris - Suspensory ligaments - Ciliary body - Cornea - Sclera - Choroid - Retina - Anterior segment - Posterior segment - Anterior chamber - Posterior chamber - Canal of Schlemn

Answer 42

Find image of eye? idk

Question 43

Canal of Schlemn: where is it located, what does it do, and what is the rate of drainage?

Answer 43

Located at the iridocorneal angle Drains aqueous humour using 25-35 collector channels after it has travelled through the trabecular meshwork 1-2µL/min - rate of formation of aqueous humour

Question 44

Intraocular pressure: what is the normal pressure and what factors determine it?

Answer 44

Normal - 10-20mmHg * Rate of formation of aqueous humour * rate of drainage of the trabecular meshwork * Pressure in the episcleral veins

Question 45

Glaucoma: what are the two types, how are they formed, what do they cause, and what do they lead to?

Answer 45

Narrow-angle - Iris inflammation, making it closer to the cornea, and narrowing the angle, covering the canal of Schlemn and preventing aqueous humour drainage Open-angle - channels draining the canal of Schlemn become blocked and aqueous humour is not properly drained * Both may lead to increased intraocular pressure and can lead to optic nerve atrophy and defects in the visual field * Peripheral fields are first lost in glaucoma, it then spreads and narrows as it worsens

Question 46

Extra reading

Answer 46

Read Toris et al (2023) The Science of Glaucoma Management. Translational Research to Next-Generation Clinical Practise. Chapter 22, pg 217-229