Eye Anatomy Flashcards
(25 cards)
What is the importance of testing a patient’s corneal reflex?
It helps evaluate the integrity of the trigeminal nerve and facial nerve, as well as the sensitivity of the cornea.
Discuss the method of testing a patient’s corneal reflex (3)
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
Corneal reflex:
Which nerve conveys the afferent signal?
Trigeminal nerve
Corneal reflex:
Which nerve conveys the efferent signal?
Facial nerve
Corneal reflex:
Which muscle delivers the response?
Levator Palpebrae Superioris
Cornea vs. Conjunctiva:
Structure
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
Cornea vs. Conjunctiva:
Function
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
Identify and describe which bones form the orbit:
Roof (superior wall)
Frontal bone and the lesser wing of the Sphenoid
Frontal bone separates the orbit from the anterior cranial fossa
Identify and describe which bones form the orbit:
Floor (inferior wall)
Maxilla, Palatine and Zygomatic bones
Maxilla separates the orbit from the underlying maxillary sinus
Identify and describe which bones form the orbit:
Medial wall
Ethmoid, Maxilla, Lacrimal and Sphenoid bones
Ethmoid bone separates the orbit from the ethmoid sinus
Identify and describe which bones form the orbit:
Lateral wall
Zygomatic bone and greater wing of the Sphenoid
Identify and describe which bones form the orbit:
Apex
Base
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)
Describe 2 structures that pass through the Optic Canal
- Optic nerve
- Ophthalmic arteries
Describe 6 structures that pass through the Superior Orbital Fissure
- Oculomotor nerve
- Trochlear nerve
- Ophthalmic branch of Trigeminal
- Abducens nerve
- Ophthalmic veins
- Sympathetic fibres
Name the 7 extra-ocular muscles
- Levator Palpebrae Superioris
- Superior Rectus
- Inferior Rectus
- Medial Rectus
- Lateral Rectus
- Superior Oblique
- Inferior Oblique
Functions of 7 extra-ocular muscles
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
What is unusual about the Superior Oblique muscle?
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.
Oculomotor:
Origin, Pathway, Foramen, Targets
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
Trochlear:
Origin, Pathway, Foramen, Targets
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)
Abducens:
Origin, Pathway, Foramen, Targets
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)
Function of Pupillary Sphincter
constricts the pupil, reducing the amount of light entering the eye
Function of Ciliary muscles
contracts, causes the lens to become more spherical, and this more adapted to short range vision
Which cranial nerve delivers the parasympathetic innervation of the pupillary sphincter and ciliary muscles?
Oculomotor
From which nucleus in the brainstem do the pre-ganglionic neurons originate?
Edinger-Westphal nucleus
