Anatomy: Reflexes of the Eye Flashcards
Name the muscle fibres responsible for pupillary dilation in response to sympathetic stimulation
Dilator pupillae fibres
What is the oculocardiac reflex?
Reflex bradycardia in response to tension on extraocular muscles or pressure on the eye
Name the muscle fibres responsible for pupillary constriction in response to parasympathetic stimulation
Sphincter pupillae fibres
In the corneal (blink) reflex, the central CNS connections are between CN V and CN ____
CN VII
Name the cranial nerve which is responsible for sensory innervation of the face
Branches of CN V (trigeminal nerve)
What is the function of basal tears?
Involved in corneal health - clean/nourish and hydrate cornea, involved in corneal health
Name the muscle which alters the change of the lens in the lens accommodation reflex
Ciliary body
What is the function of the lens accommodation reflex?
Change in the shape of the lens to focus on a near or further away object
What is the vestibulo-ocular reflex?
Turns the eyes in the opposite direction to a head movement to stabilise gaze on an object during head movement
What is the function of reflex tears?
Extra tears in response to mechanical or chemical stimulation
Where do CNS connections occur in the pupillary light reflex?
Midbrain in a 4 neurone chain
In ‘far vision’, how does the shape of the lens change?
Ciliary muscle relaxes, ligament tightens and lens flattens
Which cranial nerve is responsible for the motor (efferent) limb of the pupillary light reflex?
Bilateral via CN III → bilateral constriction
What is a ‘fixed-dilated (‘blown’) pupil?
Often a serious pathological sign (e.g. of CN III pathology)
In the pupillary light reflex, a _____ light reflex occurs in the non-stimulated eye
Consensual
Name the muscle responsible for the wide eye opening of fight or flight
Mueller’s muscle of LPS (involuntary - sympathetic innervation)
How would you clinically assess the lens accommodation reflex?
Clinically assess all 3 components of the reflex:
- Bilateral pupillary constriction (parasympathetic constriction of sphincter pupillae)
- Bilateral convergence of both eyes towards midline (medial rectus)
- Bilateral relaxation of the lens (lens becomes spherical due to contraction of the ciliary muscles)
Describe the effect of parasympathetic stimulation on the eye
Get less light into into eyes (to protect the retina from bright light or when asleep), focus on near objects, reflex lacrimation (to wash away stimulant foreign body and clean the cornea)
What is a mydriatic pupil?
A non-physiologically enlarged pupil (e.g. from mydriatic drugs which induce dilation of the pupil)
Which cranial nerve is responsible for the sensory (afferent) limb of the pupillary light reflex?
Ipsilateral CN II
The ciliary muscle ____ in ‘near vision’
Contracts
Which regions of the face are given sensory innervation by CN V2 (maxillary nerve)?
Skin of the lower eyelid, skin over the maxilla
Describe the pathway of postsynaptic sympathetic fibres from the superior cervical sympathetic ganglion to the orbit
Superior cervical sympathetic ganglion → internal carotid nerve → internal carotid plexus → axons carried on ophthalmic artery and on its branches to orbital structures
What is the function of the corneal (blink) reflex?
Protective function - protects the eyes from foreign bodies and bright lights
In the pupillary light reflex, a _____ light reflex occurs in the stimulated eye
Direct
In ‘near vision’, how does the shape of the lens change?
Ciliary muscle contracts, ligament relaxes and lens becomes spherical
Which cranial nerves are responsible for the sensory (afferent) limb of the corneal (blink) reflex?
Action potentials conducted from cornea via CN V1 branches
To trigenimal ganglion, then along CN V to pons
What is the corneal (blink) reflex?
Involuntary blinking of the eyelids elicited by stimulation of the cornea
Name the nerves involved in the oculocardiac reflex
CN V1 and CN X
Which regions of the face are given sensory innervation by CN V3 (mandibular nerve)
Skin over mandible and TMJ, except over angle of mandible
What is a miotic pupil?
Non-physiologically constricted pupil (e.g. a component of Horner’s syndrome)
Describe the effect of sympathetic stimulation on the eye
Eyes open wider to get more light into eyes, may help focus on far objects, emotional lacrimation
Which cranial nerves are responsible for the motor (efferent) limb of the corneal (blink) reflex?
Action potentials conducted via CN VII to eyelid part of orbicularis oculi
What is a fixed ‘pin point’ pupil?
Often a serious pathological sign (e.g. opiate drugs)
Describe the arrangement of the sphincter pupillae fibres
Encircle pupil around the internal cicumference of iris
The ciliary muscle ______ in ‘far vision’
Relaxes
Which regions of the face are given sensory innervation by CN V1 (ophthalmic nerve)?
Upper eyelid, cornea, conjunctiva
The ___________ division of the ANS is responsible for contraction of the ciliary muscle to accommodate the lens in near vision
Parasympathetic
Which branch of the ANS is responsible for emotional tears?
Sympathetic
Describe the arrangement of the dilator pupillae fibres
Radially arranged - fixed origin around external circumference of iris, mobile insertion around internal circumference
Name the cranial nerves responsible for the efferent limb of the lacrimation reflex
Parasympathetic axons originating from CN VII
Name the cranial nerves responsible for the afferent limb of the lacrimation reflex
CN V1 from cornea/conjunctiva
Name the nerves involved in the vestibulo-ocular reflex
CN VIII and CNs III, IV and VI
