3. Orbit, Eyelids and Eyes

Question 1

What are the bones of the orbit?

Answer 1

Question 2

Describe the structure of the eyelids.

Answer 2

• Each eyelid contains a cartilaginous tarsal plate, attached to the margins of the orbit by the orbital septum, and the medial and lateral palpebral ligaments.
• Superficial to these lies the palpebral part of the facial muscle orbicularis oculi which contracts reflexively (blinking reflex) to close the eyelids in response to potentially dangerous stimuli such as sudden flashes of light, or to stimulation of the cornea.

Question 3

What are the different muscles responsible for eye movement?

Answer 3

• Lateral rectus muscle -> Abduction
• Medial rectus muscle -> Adduction
• Superior rectus muscle -> Elevation + Adduction
• Inferior rectus muscle -> Depression + Adduction
• Superior oblique muscle -> Depression (counter-intuitive) + Abduction + Inward rotation
• Inferior oblique muscle -> Elevation (counter-intuitive) + Abduction + External rotation

Question 4

Descrive the nerves involved in the lacrimal gland and blink (corneal) reflexes.

Answer 4

Lacrimal reflex

• Afferent: Ophthalmic branch of trigeminal
• Efferent: Parasympathetic facial nerve

Blink reflex

• Afferent: Ophthalmic branch of trigeminal
• Efferent: Facial nerve (to orbicularis oculi)

Question 5

What is levator palpabrae innervated by?

Answer 5

• Oculomotor nerve
• Sympathetic fibres

Question 6

What can lead to ptosis?

Answer 6

• Oculomotor nerve lesion
• Sympathetic lesion -> e.g. tumour of lung apex (Pancoast’s) affecting superior cervical ganglion

Question 7

How does a palsy of each of CN 3, 4 and 6 present?

Answer 7

Question 8

Draw a diagram of the axial section of the eye, showing the anterior and posterior chambers.

Answer 8

Question 9

Describe the circulation of aqueous humour in the eye.

Answer 9

• Aqueous humour, which provides nutrients for the avascular cornea and lens, occupies the anterior segment of the eyeball.
• The anterior segment is subdivided into the anterior and posterior chambers.
• The anterior chamber is located between the cornea anteriorly and iris posteriorly.
• The posterior chamber, where aqueous humour is produced by the ciliary processes of the ciliary body, is located between the iris anteriorly and the lens posteriorly

Question 10

What is raised intraocular pressure called?

Answer 10

Glaucoma

Question 11

What can be used to measure intraocular pressure?

Answer 11

Ophthalmoscope

Question 12

Draw a diagram of the anterior segment of the eye.

Answer 12