Eye Anatomy

Question 1

What is the importance of testing a patient’s corneal reflex?

Answer 1

It helps evaluate the integrity of the trigeminal nerve and facial nerve, as well as the sensitivity of the cornea.

Question 2

Discuss the method of testing a patient’s corneal reflex (3)

Answer 2

1) gently touch the cornea of one eye using a clean cotton swab

2) watch for patient’s response to the corneal stimulation, a normal response involves bilateral blinking of both eyes (blink reflex) - this is mediated by the Trigeminal nerve (afferent limb) sensing the stimulus, and the Facial nerve (efferent limb) causing the eyelid to close

3) assess symmetry by comparing the response between both eyes - asymmetry in the blink reflex may indicate dysfunction of the Trigeminal nerve or Facial nerve on the affected side

Question 3

Corneal reflex:

Which nerve conveys the afferent signal?

Answer 3

Trigeminal nerve

Question 4

Corneal reflex:

Which nerve conveys the efferent signal?

Answer 4

Facial nerve

Question 5

Corneal reflex:

Which muscle delivers the response?

Answer 5

Levator Palpebrae Superioris

Question 6

Cornea vs. Conjunctiva:

Structure

Answer 6

Cornea:

composed of 5 layers - Epithelium, Bowman’s layer, Stroma, Descemet’s membrane, and Endothelium

Conjuntiva:

consists of non-keratinised stratified squamous epithelium with Goblet cells that produce Mucin, which helps lubricate the ocular surface

Question 7

Cornea vs. Conjunctiva:

Function

Answer 7

Cornea = main refractive element of the eye; responsible for focusing light onto the retina

Conjunctiva = helps lubricate and protect the ocular surface by producing mucin and tears

also plays a role in immune defence by containing lymphoid tissue and contributing to the production of antibodies

Question 8

Identify and describe which bones form the orbit:

Roof (superior wall)

Answer 8

Frontal bone and the lesser wing of the Sphenoid

Frontal bone separates the orbit from the anterior cranial fossa

Question 9

Identify and describe which bones form the orbit:

Floor (inferior wall)

Answer 9

Maxilla, Palatine and Zygomatic bones

Maxilla separates the orbit from the underlying maxillary sinus

Question 10

Identify and describe which bones form the orbit:

Medial wall

Answer 10

Ethmoid, Maxilla, Lacrimal and Sphenoid bones

Ethmoid bone separates the orbit from the ethmoid sinus

Question 11

Identify and describe which bones form the orbit:

Lateral wall

Answer 11

Zygomatic bone and greater wing of the Sphenoid

Question 12

Identify and describe which bones form the orbit:

Apex
Base

Answer 12

Apex - located at the opening of the optic canal, the optic foramen

Base - opens out into the face, and is bounded by the eyelids (aka Orbital rim)

Question 13

Describe 2 structures that pass through the Optic Canal

Answer 13

• Optic nerve
• Ophthalmic arteries

Question 14

Describe 6 structures that pass through the Superior Orbital Fissure

Answer 14

• Oculomotor nerve
• Trochlear nerve
• Ophthalmic branch of Trigeminal
• Abducens nerve
• Ophthalmic veins
• Sympathetic fibres

Question 15

Name the 7 extra-ocular muscles

Answer 15

• Levator Palpebrae Superioris
• Superior Rectus
• Inferior Rectus
• Medial Rectus
• Lateral Rectus
• Superior Oblique
• Inferior Oblique

Question 16

Functions of 7 extra-ocular muscles

Answer 16

Levator Palpebrae Superioris
- Elevation of upper eyelid

Superior Rectus
- Elevation of eyeball

Inferior Rectus
- Depression of eyeball

Medial Rectus
- Adduction of eyeball

Lateral Rectus
- Abduction of eyeball

Superior Oblique
- Depression, Abduction and Medial rotation of eyeball

Inferior Oblique
- Elevation, Abduction and Lateral rotation of eyeball

Question 17

What is unusual about the Superior Oblique muscle?

Answer 17

It has a distinctive path compared to the other eye muscles.

Instead of running straight from origin to insertion, the superior oblique muscle’s tendon passes through a pulley-like structure (called the trochlea) before attaching to the eyeball.

This unique path allows it to exert its force at an angle, contributing to the complex movements of the eye.

Question 18

Oculomotor:

Origin, Pathway, Foramen, Targets

Answer 18

Origin = anterior surface of midbrain

Pathway = both fibres emerge from the midbrain, runs forward towards orbit. The somatic motor fibres branch out into 4/6 muscles of the eye to allow its movement in the socket, and another muscle, which lifts up the upper eyelid.

Foramen = Superior Orbital Fissure

Targets = 4 extra-ocular muscles, Levator Palpebrae Superioris, pupillary Sphincter

Question 19

Trochlear:

Origin, Pathway, Foramen, Targets

Answer 19

Origin = posterior surface of midbrain

Pathway = wraps around midbrain and travels anteriorly towards orbit; innervates the superior oblique muscle

Foramen = Superior Orbital Fissure

Targets = Superior Oblique muscle (extra-ocular eye muscle)

Question 20

Abducens:

Origin, Pathway, Foramen, Targets

Answer 20

Origin = Pontomedullary Junction

Pathway = runs anteriorly from the pons and medulla junction, towards the orbit, to innervate the lateral rectus muscle, which abducts the pupil

Foramen = Superior Orbital Fissure

Targets = Lateral Rectus muscle (extra-ocular eye muscle)

Question 21

Function of Pupillary Sphincter

Answer 21

constricts the pupil, reducing the amount of light entering the eye

Question 22

Function of Ciliary muscles

Answer 22

contracts, causes the lens to become more spherical, and this more adapted to short range vision

Question 23

Which cranial nerve delivers the parasympathetic innervation of the pupillary sphincter and ciliary muscles?

Answer 23

Oculomotor

Question 24

From which nucleus in the brainstem do the pre-ganglionic neurons originate?

Answer 24

Edinger-Westphal nucleus

Question 25

Which ganglion contains the post-ganglionic neurons?

Answer 25

Ciliary ganglion