they eye and vision

Question 1

describe the sclera

Answer 1

• tough fibrous outer coat, protection, made of collagen
• Forms whit capsule, except anterior surface where it is specialised into the clear cornea
• Serves as an insertion point for the external muscles of the eye
• Continuation of dura mater and cornea

Question 2

describe the cornea

Answer 2

• Light transmission, must be transparent
• Barrier to trauma and infection – must be tough
• refraction
• smooth spherical surface

Question 3

describe the iris

Answer 3

• contains dilator (sympathetic, radial fibres) and sphincter pupillae muscles (parasympathetic, circular fibres)
• both innervated by oculomotor nerve via ganglion
• pupillary reflexes
• specialised section of choroid

Question 4

describe the ciliary body

Answer 4

• Glandular epithelium produces aqueous humour – processes; aqueous humour & nutrients for cornea & lens
• Ciliary (smooth) muscle controls accommodation

Question 5

choroid

Answer 5

• blood supply/nutrition to outer third of retina (photoreceptors)
• Heat sink
• Darkly pigmented so that it can absorb stray photons

Question 6

what is in the middle layer of the eye? (uvea)

Answer 6

iris
ciliary body
choroid

Question 7

describe how the retina works

Answer 7

• Light passes through the pupil from the visual field to project an image onto the retina. An object that attention is focused on, projects an image that is centred near the posterior pole of the eye along the visual axis – fovea centralis. The surrounding 1cm is known as the Macula lutea at these points the retina is specifically modified for maximal visual acuity
• Medial to the macula is a region where retinal axons accumulate to leave the eye this is the optic disc (where the optic nerve forms) photoreceptors are absent in this region – blind spot
• Retinal pigment epithelium (RPE) – contains photoreceptors so it is able to convert light into electrical impulses – photoelectric transducer

Question 8

aqueous humour

Answer 8

contains water and electrolytes
• Nutrition to lens and cornea
• Maintains intraocular pressure, by production and drainage
• Produced by glandular epithelium of ciliary body – travels forward
• Drain – trabecular meshwork
• Contains both anterior and posterior chambers
• Made of smooth muscle which controls accommodation
• Parasympathetic

Question 9

lens

Answer 9

• Biconvex
• Responsible 1/3 refractive power of eye
• Accommodation

Question 10

hypermetropia

Answer 10

Underpowered to focus near objects on retina 
May be due to:
•	Corneal curvature too shallow 
•	Lens not flexible enough 
•	Axial length of eyeball too short 
•	Fixed with converging lens

Question 11

myopia

Answer 11

Overpowered so cant focus objects on retina
May be due to
• Corneal curvature to steep
• Axial length of eyeball too long

Question 12

what is in the posterior segment

Answer 12

• Vitreous humour
• Avascular viscoelastic gel
• Hyaluronic acid (GAG)
• Collagen

Question 13

what makes up the Adnexae

Answer 13

eyelids, conjunctiva, tear film

Question 14

lids

Answer 14

protect the eye
• Orbicularis oculi muscle – closure of eyelid
• Levator palpebrae superioris (oculomotor, opens eyelid) & sympathetic muscle

Question 15

conjunctiva palpebral

Answer 15

• Conjunctival fornix
• Limbal stem cells
• Mucous membrane (goblet cells)
• Lymphoid cells (protective)
• Highly vascular

Question 16

tear film

Answer 16

• 3 layers: anterior lipid (oils – secreted by meibomium glands, hydrophobic barrier to prevent the aqueous layer evaporating), middle aqueous (water, electrolytes, proteins – secreted by lacrimal glands, regulates transport through the cornea and prevent infection) , posterior mucous (secreted by goblet cells, hydrophilic layer that allows for the even distribution of the tear film)
• Protective
• Nutrition for cornea

Question 17

layers through which a photon must travel through the eye

Answer 17

1) Tear film (transmission)
2) Cornea (transmission & 2/3 refraction)
3) Aqueous humour (transmission)
4) Lens (transmission & refraction)
5) Vitreous humour (transmission)
6) Ganglion cell (transmission)
7) Amacrine cell (transmission)
8) Bipolar cell (transmission)
9) Horizontal cell (transmission)
10) Cone (transduction)
11) Rods (transduction)
12) Pigmented epithelium (absorption of excess photons)

Question 18

arterial supply of eye

Answer 18

Internal carotid a. → ophthalmic a.
• Branches of ophthalmic a. (ocular group):
Central retinal a.
Posterior ciliary a. → long and short posterior ciliary a.
Muscular a. → anterior ciliary a.
• branches of ophthalmic artery (orbital group)
lacrimal a.
several other arteries supply face and lips
external carotid a.→ facial a.→ angular a.

Question 19

blood supply - inner retina

Answer 19

blood supply – inner retina
• inner 2/3 retina supplied by central retinal a.
• branches into superior/inferior/temporal/nasal branches
• drained by branch retinal veins → central retinal v.→ ophthalmic retinal v.→ cavernous sinus→ internal jugular v.

Question 20

blood supply - outer retina

Answer 20

• outer 1/3 supplied by choroid
• posterior ciliary a. → choroidal a.→ choriocapillaris
• blood-retinal barrier at RPE
regulates movement of nutrition and solutes from choroid into subretinal space

Question 21

lymphatics of eye

Answer 21

No lymphatic drainage from the globe

Conjunctiva and lids do have lymphatic drainage to submandibular and pre-auricular nodes