16.5.2 Orbit and Eye Flashcards
A
Ciliary body
B
Iris
C
Lens
D
Aqueous humour
E
Cornea
F
Canal of Schlemm
G
Conjunctiva
H
Fovea
I
Optic disk
J
Sclera
K
Choroid
L
Retina
M
Macula
N
Vitreous humor
Main function of ciliary body
Produce aqueous humor
Active accommodation
Main function of optic disc
Point of exit for ganglion cell axons leaving the eye (blindspot)
Main function of cornea
Refract light
Main function of sclera
Protect inner contents of the eye from mechanical trauma
What is the afferent nerve involved in the corneal (blink) reflex?
Ophthalmic branch of trigeminal (V1)
What is the efferent nerve involved in the corneal (blink) reflex?
Facial (VII) to the orbicularis oculi
Where would the lesion most likely be in a patient presenting with bitemporal hemianopsia (the temporal halves of both visual fields are blind)?
Optic chiasm
(X-shaped structure at the base of the brain where two optic nerves meet and cross. Fibres carrying information from the nasal/medial halves of each retina cross to the opposite side of the brain, while fibres carrying information from the temporal/lateral halves of each retina continue on the same side)
What would be the consequence on the visual field in patients with lesions of the optic nerve?
Complete bilateral loss of vision
For the pupillary light reflex, name the afferent nerve
Optic nerve (II)
For the pupillary light reflex, name the efferent nerve
Parasympathetic fibres of the oculomotor nerve (III)
For the pupillary light reflex, name the muscle supplied by the efferent nerve
Sphincter pupillae
Which muscles control convergence of the eyes?
Medial rectus
What is the action of the superior oblique muscle?
Rotates the top of the eye towards the nose (intorsion)
Moves the eye downwards (depression)
Moves the eye outwards (abduction)
Which nerve innervates the lateral rectus muscle?
Abducens (VI)
A
Canal of Schlemm
B
Ciliary body
C
Cornea
D
Iris
T/F - Structure A drains aqueous humor back to the circulatory system
True
T/F - Structure B contains striated muscle
False
T/F - Structure C is optically transparent
True
T/F - Radially arranged smooth muscle in structure D contracts in response to sympathetic stimulatio
True
T/F - Structure B connects to the lens via suspensory fibres
True
Glaucoma is caused by
Increased intraocular pressure due to reduced drainage of the vitreous humor via the trabecular network and the canal of Schlemm
What movements of the front of the eye or the eyelid would be caused by the medial rectus acting alone?
Adduction
What movements of the front of the eye or the eyelid would be caused by the superior oblique acting alone?
Rotates the top of the eye towards the nose (intorsion)
Moves the eye downwards (depression)
Moves the eye outwards (abduction)
What movements of the front of the eye or the eyelid would be caused by the Inferior oblique acting alone?
Rotates the top of the eye away from the nose (extorsion)
Moves the eye upwards (elevation)
Moves the eye outwards (abduction)
What movements of the front of the eye or the eyelid would be caused by the ciliary body acting alone?
Accommodation reflex
Using the diagram, select the structure involved in the drainage of aqueous humor
L
(Canal of Schlemm)
Using the diagram, select the structure involved in actively controlling the accommodation
D
(Ciliary body)
Using the diagram, select the posterior chamber of the eye
B
(Vitreous humor)
What is the cause of papilloedema?
Increased intracranial pressure causing the optic disc to swell.
What is this?
Papilloedema
The cranial nerve supplying parasympathetic fibres to the pupillary constrictor muscle
Oculomotor (III)
Using the diagram, select the structure that provides the greatest focusing power for the information of the retinal image
I
(Cornea)
Concerning the normal pupillary light reflex, when one eye is illuminated…
Both pupils should constrict (consensual response)
Concerning the normal pupillary light reflex, the afferent nerve of the reflex is
Optic (II)
Concerning the normal pupillary light reflex, the efferent nerve of the reflex is
Oculomotor (III)
Papilloedema is characterised by
Blurred optic disk and swollen blood vessels seen on ophthalmic examination
Which cranial nerve carries the autonomic fibres which stimulate lacrimation?
CNVII (facial nerve)
What effect would stimulation of the oculomotor nerve have on the pupil?
Constriction of the pupil (pupillary light reflex)
Identify the function of the structure indicated by 3
Focusing of light onto the retina
(Ciliary body)
Identify the structure indicated by 2
Canal of Schlemm
Which nerves control the muscle found in the structure indicated 3?
Parasympathetic postganglionic neurons
What material is found in the region indicated by 4?
Aqueous humor
(Anterior chamber)
What consequence would occur as a result of a blockage in the structure 2?
Raised intraocular pressure
(Eventually glaucoma)
Which nerve supplies preganglionic, efferent innervation for the lacrimal gland?
- Abducens
- Facial
- Oculomotor
- Trigeminal
- Trochlear
Facial (parasympathetic)
What is the afferent for the lacrimation reflex?
Ophthalmic trigeminal
Where does the superior oblique muscle attach to the eyeball?
- Lateral aspect of the anterior sclera
- Lateral aspect of the posterior sclera
- Medial aspect of the posterior sclera
- Medial aspect of the anterior sclera
- Superior aspect of the anterior sclera
Lateral aspect of the posterior sclera
Extraocular muscles
- Superior rectus
- Inferior rectus
- Lateral rectus
- Medial rectus
- Superior oblique
- Inferior oblique
Superior rectus
Inferior rectus
Medial rectus
Lateral rectus
Superior oblique
Inferior oblique
Extraocular muscles supplies by CNIII (oculomotor)
- Superior rectus
- Inferior rectus
- Medial rectus
- Inferior oblique
Extraocular muscles supplied by CNIV (trochlear)
- Superior oblique
Extraocular muscles supplied by CNVI (abducens)
- Lateral rectus
Superior oblique movement
Rotates the top of the eye towards the nose (intorsion)
Moves the eye downwards (depression)
Moves the eye outwards (abduction)
Inferior oblique movement
Rotates the top of the eye away from the nose (extorsion)
Moves the eye upwards (elevation)
Moves the eye outwards (abduction)
Which nerve/muscle is damaged in the right eye?
Oculomotor nerve (III)
Which nerve/muscle is damaged in the left eye?
Trochlear nerve (IV)
Which muscle is paralysed? Which side?
Left lateral rectus
Which nerve supplies the paralysed muscle?
Abducens (VI) nerve
What symptom would the man notice?
Diplopia while looking left
1
Pretectal nucleus
2
Edinger-Westphal nucleus
3
Oculomotor nerve (III)
4
Optic nerve (II)
5
Ciliary ganglion
6
Short ciliary nerve
7
Sphincter pupillae muscle
Afferent component of pupillary light reflex
Optic nerve (II)
Efferent component of pupillary light reflex
Oculomotor nerve (III)
The site of termination of afferent nerves in the pupillary light reflex
Pretectal nucleus
The nucleus of origin of the efferent nerves in the pupillary light reflex
Edinger-Westphal nucleus
Axons from the pretectal nucleus project to the contralateral Edinger-Westphal nucleus via
The posterior commissure
When one eye is illuminated, what should happen due to the pupillary light reflex
Both pupils constrict
Which nerve(s) is damaged in this case?
Efferent pathway of left eye:
Oculomotor (III)/short ciliary nerve
Which nerve(s) is damaged in this case?
Afferent pathway of left eye:
Optic (II) nerve
Pupil constriction in the pupillary light reflex is under what control
Parasympathetic
Pupil dilation is under what control
Sympathetic
Role of suspensory ligament
- Connect the lens to the ciliary body
- Maintain passive, forward gaze
Lacrimation
Secretion of tears
What are the lacrimal glands?
- Paired exocrine glands that secrete the aqueous layer of the tear film
What is the nasolacrimal duct?
- Also known as the tear duct
- Carries tears from the lacrimal sac of the eye into the nasal cavity
- Duct begins in the eye socket (between the maxillary and lacrimal bones), from where it passes posteriorly and inferiorly
- This duct allows the draining of tears into the nasal cavity, where they will then be removed or ingested and components broken down in the stomach
- [This means that if there is a blockage in the duct, the eyes are not drained, causing them to become watery and at higher risk of infection]
What is the levator palpebrae superioris and what innervation does it receive?
- Elevates the superior/upper eyelid, skeletal muscle
- Innervation: Oculomotor nerve (CN III)
How does Horner’s syndrome affect the eye?
- Horner’s syndrome is when lesion of the sympathetic supply leading to:
- Miosis (constriction of the pupil)
- Ptosis
- Anhidrosis (lack of sweating on the face)
- Enophthalmos (sinking of the eye into the orbit)
What is ptosis?
drooping eyelid, due to interruption of innervation to the superior tarsal muscle (by failure of the sympathetic or oculomotor nerve (CNIII)
How does the eye develop during CNS development?
As an outgrowth of the forebrain.
What is this?
Ciliary muscles
What is this?
Central artery of retina
1
Posterior chamber
2
Anterior chamber
What is this?
Ciliary processes
What are the signs of raised intracranial pressure?
*Paillodema
*Dilation of retinal veins
Why is there dilation of retinal veins when intracranial pressure is raised?
this occurs do to occlusion of the exiting veins, as these travel in the same channel as the optic nerve, so the increased pressure will reduce flow
Which is a normal retina? What pathology can be seen?
Left
Papilloedema
What is the optic nerve surrounded by?
The optic nerve is surrounded by the subarachnoid space, which is continuous with that around the brain and contains CSF
What are the two main parts of the eye involved in focusing light to form an image on the retina?
- Cornea
- Lens
What are cataracts?
- An opacification of the lens, which leads to decreased vision
- Can be bilateral or unilateral
- Most develop due to changes in the tissue due to injury or ageing
- There are some inherited genetic disorders that cause other health problems and increase your risk of cataracts
- Can also be caused by other eye conditions, previous eye surgery or medical conditions such as diabetes
What is the function and innervation of the ciliary muscles?
- The muscles are dually innervated by the autonomic nervous system
- Parasympathetic innervation activates the muscle for contraction
- Sympathetic innervation has an inhibitory effect on the level of parasympathetic activity
- Contraction and relaxation of the ciliary muscles changes the thickness and curvature of the lens, therefore controlling the focussing power of the eye
- Contraction of the muscle allows for the lens to bunch up, increasing its focussing power (the suspensory ligaments are allowed to become slack)
- Relaxation of the ciliary muscles causes the lens to become thinner and flat, decreasing the focussing power (the suspensory ligaments become stretched/tight)
What is the dilator pupillae and what innervation does it receive?
- This is the radial muscle of the iris that is able to dilate the pupil
- It receives sympathetic innervation (long ciliary nerves, non-myelinated sympathetic fibres)
- Its parasympathetic innervation appears less significant
What is the sphincter pupillae and what innervation does it receive?
- This is a muscle that controls the size of the pupil
- The sphincter muscles are located near the pupillary margin and contraction of this muscle will cause the pupil to become smaller
- The muscle is innervated by parasympathetic fibres (short ciliary nerves)
What drugs can be used to dilate the pupil?
*Alpha muscarinics
* Cyclopentolate -> Muscarinic antagonist, commonly used as an eye drop during paediatric eye examinations to dilate the eye (mydriatic) and prevent focussing (cycloplegic)
What movement does the lateral rectus cause?
Abduction
