Eye

Question 0

Describe the borders of the eye orbit

Answer 0

Roof: frontal and sphenoid bones
Floor: maxilla, zygomatic, palatine
Medial: ethmoid, maxilla, lacrimal
Lateral: zygomatic and sphenoid

Question 1

Describe the basic anatomy of the eye

Answer 1

Outer layer: sclera and cornea (CN V1)
- anterior chamber between cornea and iris

Middle layer: choroid (red reflex), ciliary body and iris (PNS constricts pupil: sphincter pupillae; SNS dilates pupil: dilator pupillae)

• Posterior chamber between iris, ciliary body and lens
• ciliary body secretes aqueous humour
• cavity behind lens is vitreous humour (jelly like)

Inner layer: retina

• optic disc (optic nerve) located at fundus of retina: medial aspect
• fovea is a depression in the centre of the macula (acute vision): central

Question 2

Discuss the major orbital fossa and their contents

Answer 2

Optic canal: optic nerve, ophthalmic artery

Superior orbital fissure: MNEMONIC
(large French teenagers sit numb in anticipation of sweets)
Lacrimal nerve: CN V1
Frontal nerve: CN V1
Trochlear nerve: CN IV
Superior branch of oculomotor nerve: CN III
Nasociliary nerve: branch of CN V1
Inferior branch of oculomotor: CN III
Abducens nerve: CN VI
Opthalmic veins
Sympathetic fibres

Question 3

Discuss the extra ocular muscles and their function

Answer 3

Recti

• superior rectus: look up. CN III
• inferior rectus: look down. CN III
• medial rectus: look medial (to nose). CN III
• lateral rectus: look lateral (look outward). CN VI

Obliques

• superior oblique: look down and in (passes through trochlear) CN IV
• inferior oblique: look up/out. CN III

Levator palpebrae superioris
- lifts eyelids (merges with superior oblique). CN III

LR6. SO4. R3

Question 4

Briefly discuss eye disorders

Answer 4

Thyroid disease- exophthalmos (protruding eye)
Ageing- lens hardens/flattens affecting focussing (presbyopia)
Ageing- partial/complete lens opacity (cataract)
Blunt trauma- anterior chamber haemorrhage (hyphema)
Raised ICP- compress optic nerve/blood vessels (retinal oedema).
Papilloedema- bulging optic disc due to raised ICP causing blindness
Detached retina- intra retinal space reopens up between the two layers of the retina
Enopthalmos- eyeball pushed in (pulsatile) due to infra orbital bleeding

Question 5

Briefly discuss the eye palsies

Answer 5

CN VI: ABDUCENS nerve palsy

• loss of lateral rectus innervation
• eye remains fully adducted

CN IV: TROCHLEAR nerve palsy

• loss of superior oblique innervation
• unable to look down when eye is adducted (reading muscles)

CN III: OCULOMOTOR nerve palsy

• loss of all other eye muscles
• ptosis: upper eyelid droops - loss of levator palpebrae superioris
• pupil fully dilated - loss of sphincter pupillae (SNS)
• eye moves down and out - unopposed action of lateral rectus and superior oblique

Question 6

Briefly discuss the blood supply of the eye

Answer 6

Arterial supply

• External carotid artery branches to infra orbital artery
• Internal carotid artery branches to Opthalmic artery, then to central artery of the retina (obstruction of the latter causes instant blindness)

Venous drainage

• inferior Opthalmic vein, cavernous sinus, Opthalmic vein, marginal vein to facial vein
• superior Opthalmic vein, cavernous sinus or Opthalmic vein, marginal vein to facial vein
• central vein of retina drains to cavernous sinus

Blockage of cavernous sinus can cause infections which can track back to the brain

Question 7

Discuss the functioning of the eyelids

Answer 7

Strengthened by inferior and superior tarsal muscles
- glands lubricate edges to stop them sticking together

OPENING:

• levator palpebrae superioris via CN III - damage causes ptosis of UPPER eyelid!
• superior tarsal muscles via sympathetic fibres - partial ptosis if damaged

CLOSING:
- orbicularis oculi via CN VII - can result in dry eyes of eyelids don’t close properly

Lacrimal ducts: lacrimal fluid (physiological saline and lysozyme)
- lie in lacrimal fossa, fluid conducted via lacrimal ducts to conjunctival sac
Lacrimal canaliculi: found in corner of the eye, drain lacrimal fluid to lacrimal sac
Nasolacrimal duct: convey lacrimal fluid to inferior nasal meatus

Question 8

Define the flowing: myopia, hyperopia/hypermetropia, and presbyopia

Answer 8

Myopia: short sightedness - image focused in front of the retina

Hyperopia/hypermetropia: far sightedness - image focused behind the retina

Presbyopia: far sightedness due to age related lens changes

Question 9

Define glaucoma, mydriasis, and coloboma.

Answer 9

Glaucoma: outflow of aqueous humour is blocked (via sclera venous sinus) causing an increase in intra ocular pressure. This may obstruct the central artery of the retina

Mydriasis: blown pupil

• possibly due to under active PNS or overactive SNS
• may be due to raised ICP

Coloboma: absence of a section of the iris
- developmental defect of the eye occurring during embryological development

Question 10

Describe Horners syndrome

Answer 10

Interrupted sympathetic fibres due to lesion of cervical sympathetic trunk

• MIOSIS: constricted pupil due to unopposed PNS activity
• PTOSIS: loss of superior tarsal muscle innervation
• VASODILATION: redness due to loss of sympathetic tone
• ANHYDROSIS: inability to sweat due to loss of sympathetic activity

Question 11

What so the difference between a meibomian cyst and a stye?

Answer 11

Meibomian cyst: blocked tarsal gland beneath the eyelash (within the eyelid)

Style: infection of the sebaceous gland at the base of an eyelash