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Flashcards in Anatomy Deck (27):
1

Lacrimal system: Tear film

3 layers of tear film:

1. Outer lipid layer
- secreted: Tarsal glands
- function: Retards evaporation of the aqueous layer
Prevent tears from spilling over the edge
2. Middle Aqueous layer
- secreted: Lacrimal glands
3. Inner Mucin layer
- secreted: Conjunctival goblet cells
- function: Hydrophilic surface on which aqueous layer can be spread

2

Components of the visual system (8)

1. Eye: External ocular layers and intraocular structures
2. Ocular adnexa: Eyelids and related structures
3. Orbit: Bony cavity and extraocular structures
4. Visual pathways from retina to occipital cortex
5. Cranial nerve 2, 3 , 4, 5, 6, 7
6. Sympathetic and parasympathetic supply
7. Visual association areas
8. Areas of recognition and interpretation of visual environment

3

3 external layers of the globe

OUTER: fibrous layer
1. Conjunctiva
2. Sclera
3. Cornea
MIDDLE LAYER: Vascular-muscular and pigmented layer
1. Iris
2. Ciliary body
3. Choroid
INNER LAYER: Neural layer
1. External: Retinal pigment epithelium
2. Internal: Neuroretina internally (photoreceptors)

Light pass through all layers of neuroretina to reach photoreceptors

4

3 Internal zones

1. Aqueous
2. Lens
3. Vitreous

5

Two segments of the globe

ANTERIOR SEGMENT:
1. Cornea
2. Anterior chambers
3. Iris
4. posterior chamber
5. Cililary body: Pars plana and Pars Plicata
6. Lens
7. Zonules

POSTERIOR SEGMENT:
1. Sclera
2. Choroid
3. Retina
4. Optic disc
5. Vitreous humour

6

Orbital contents

1. Eyeball
2. Fat
3. Muscle

7

Orbital blood supply

Arterial supply: Ophthalmic artery
Venous supply: Orbit → Superior and inferior ophthalmic veins→ cavernous sinus.
(Cavernous sinus thrombosis)
Veins draining skin--> Superior ophthalmic vv--> cavernous sinus

8

Orbital apex

Entry and exit of:
1. Nerves to and from the eye
2. Vessels to and from the eye
3. Site of origin of all the extraocular muscles except IO, which arises inferonasally just behind the orbital margin.

9

Conjunctiva

Characteristics
- Thin transparent mucus membrane
- Contains: bv
Distribution
- Bulbar
- Forniceal
- Palpebral
Continuous
- Skin lid margin
- Corneal epithelium- limbus

10

Sclera

Characteristics:
- Collagen Fibres
- Relatively Avascular: Pierced by bv and nn entering and leaving the interior of the eye,
- White of the eye

Distribution
- 4/5 tough, outer protective coating

Continuous
- Anteriorly: Cornea at the limbus
- Posteriorly: Dural sheath of the optic nerve

11

Cornea

Characteristics
- Avascular
- > Nerve supply
- Optically transparent.
- 5 Layers

Function:
- Refracting element

12

Uvea

1. Iris
- Where: Anterior extension
- What: Pigmented
- Function: pupil size
2. Ciliary body: Pars plana and pars plicata
- Function: Ciliary muscle--> accommodation
Aqueous secretion
3. Choroid
- Where: Located posteriorly
- Function: Blood supply

13

Retina

Characteristics:
- Inner aspects of globe
- Thin multi-layered neural tissue

Layers:
1. Ganglion cell layers
2. Interneuron
3. Photoreceptors
4. Retinal Pigment epithelium

Blood supply (choroidal and retinal):
Arterial: through optic canal→ Internal carotid aa→ Ophthalmic branch→ Central retinal aa that supply retina & Long and short Ciliary aa that supply uvea
Venous: Vortex vv, Anterior Ciliary vv, Central Retinal vv→ Superior Ophthalmic vv and Inferior Ophthalmic vv→ Cavernous sinus
Nerve: through optic canal→optic nn

Retinal structures visible with direct ophthalmoscopy
1. Optic nerve and cup
2. Central retinal aa + branches
3. Central retinal vv + branches
4. Neural retina
Macular Lutea with foveal light reflex

14

Vitreous humour

Characteristic:
- Transparent
- Avascular
- 98 % water
Insertion and attachments:
- Ora Serrata
- Optic nn head
- Macula
- Arcade vessels

15

Anatomy of the lens

The lens consists of three transparent parts:
1. Capsule: a thin outer membrane.
2. Cortex: a soft layer under the capsule. 3. 3. Nucleus: a harder central core that only develops later and is not present in children and young adults.

16

Blood and nerve supply of the lens

Does not have a nerve or blood supply. Nutrients diffuse into the lens from the aqueous and the vitreous humour.

17

Lacrimal drainage system anatomy

1. Lacrimal sac
2. Inferior punctum
3. Inferior canaliculus
4. Inferior turbinate
5. Nasalacrimal duct

18

Virteous humour apearance and consistance

Transparent gel which fills the posterior segment of the globe.--> Water 99% to weight and a network of collagen fibres is responsible for its gel-like character.

19

Vitreous humour in contact with

Encircled by the hyaloid membrane-->in contact with:
1. posterior lens capsule
2. zonules
3. pars plana epithelium
4. retina ( adhesion between posterior hyaloid membrane and retina is loose, bond stronger @ larger retinal blood vessels.)
5. optic disc.

20

Optic disc

Consists: Nerve fibres from sclera that exit at this point
Blind spot (insensitive to light): No retina and choroid

21

Muscles of the eye

1. Rectus: superior, inferior, lateral, medial
2. Oblique: Superior, Inferior
3. Trochlear

22

Eyelid

Grey line:
- divides lid margin into anterior and posterior parts.
- marginal subcutaneous fibres of orbicularis oculi.
- Anterior: eyelashes (cilia)
- Posterior: orifices of the tarsal (Meibomian) glands
- mucocutaneous junction: behind the orifices of the tarsal glands

23

Eyelid closure

1. Orbicularis oculi, an elliptical sphincter muscle: facial nerve (VII).
2. Levator palpebrae superioris lifts the upper lid: oculomotor nerve (III).
3. Superior tarsal muscle of Müller also plays a rôle in lifting the upper lid: sympathetic system.

24

Layers of the cornea

From the exterior inwards, the cornea consists of 5 layers:
1. Epithelium: 5-6 layers cells and bm and is continuous with the epithelium of the bulbar conjunctiva.
2. Bowman’s layer: Dense layer of modified stroma.
3. Stroma: 90% of the corneal thickness, and consists of lamellar fibres that run parallel to the corneal surface.
The size and periodicity of these fibres play an important rôle in the optical clarity of the cornea.
4. Descemet’s membrane: clear, elastic, basement membrane of the endothelium.
5. Endothelium: single layer of cells covering the posterior surface of the cornea.

25

Aqueous humour: secretion

Active secretion by the epithelium of the ciliary processes into the posterior chamber.

26

Aqueous humour: Circulation

Flow is through the posterior chamber and pupil into the anterior chamber.

27

Aqueous humour:Drainage

Exit from the anterior chamber is via the trabecular meshwork in the iridocorneal (drainage) angle. The fluid then enters the sinus venosus sclerae (canal of Schlemm), from which it drains into the episcleral veins.