Reflexes of the Eye

Question 1

what is the one corneal reflex

Answer 1

blink

Question 2

what does the blink reflex protect from

Answer 2

chemical and mechanical irritants

Question 3

describe the blink reflex

Answer 3

corneal APs conducted along CN V1 to the trigeminal ganglion
CNS connections connect this to CN V and the AP travels to the pons
AP then conducted down CN VII to the obicularis oculi

Question 4

how do we test the blink relfex

Answer 4

touching the patient’s sclera with a wisp of cotton wool

Question 5

what is the vestibulo-ocular reflex

Answer 5

reflex stabilises eye sight and gaze on an object during head movement, turns the eyes in the opposite direction

Question 6

through what nerves does the vestibulo-ocular reflex occur

Answer 6

CN connections between CN VIII and CN III, IV and VI

Question 7

what is the oculocardiac reflex

Answer 7

reflex bradycardia in response to tension on the extraocular muscles due or increased pressure on the eye

Question 8

describe the oculocardiac reflex pathway

Answer 8

AP travels down vagus to heart, slowing HR and relieving tension and pressure
CNS connections between CN V1 and CN X

Question 9

what is the sympathetic reflex of the eyes

Answer 9

eyes open wider to allow more light in

Question 10

what is the parasympathetic reflex of the eyes

Answer 10

• the pupil allows less light into the eyes, to protect the retina from bright lights or during sleep
• focus on near objects
• reflex lacrimation to wash away foreign object/clean cornea

Question 11

what type of muscles does the LPS contain

Answer 11

skeletal and smooth muscles

and Meullers muscle

Question 12

what is Meuller’s muscle innervated by

Answer 12

sympathetic

Question 13

how does LPS and Muellers muscle open the eyes

Answer 13

tonically contracted to maintain the opening o the eye

elevates the eyelid by an additional 2cm (usually in a sympathetic state)

Question 14

how do postsynaptic sympathetic fibres to orbital structures

Answer 14

• superior cervical sympathetic ganglion
• internal carotid nerve
• internal carotid plexus
• axons carried on the ophthalmic artery
• on ophthalmic artery branches to the orbital structures

Question 15

what is the pupillary constriction reflex

Answer 15

parasympathetics constrict the pupil in response to bright light and rest and digest

Question 16

what nerve controls the pupillary constriction reflex

Answer 16

CN III

Question 17

what happens during the pupillary constriction reflex

Answer 17

the sphincter pupillae fibres constrict decreasing the diameter of the pupil instantaneously

Question 18

what nerves control the pupillary dilation reflex

Answer 18

sympathetic

Question 19

what happens during the pupillary dilation reflex

Answer 19

the dilator pupillae muscles contract and pull on the sphincter dilating the pupils

Question 20

what is a mydriatic pupil

Answer 20

a non-physiologically enlarged pupil

Question 21

what is a mitotic pupil

Answer 21

a non-physiologically constricted pupil

Question 22

what nerve pathology is a fixed dilated pupil a sign of

Answer 22

CN III

Question 23

what is the pupillary light reflex

Answer 23

light detected by an ipsilateral optic nerve, but motor response is bilateral

Question 24

what nerve controls the pupillary light reflex

Answer 24

CN II

Question 25

what connects the lens to the ciliary body

Answer 25

suspensory ligaments

Question 26

what type of muscle is the ciliary body

Answer 26

smooth muscles, sphincter-like

Question 27

describe the process of seeing objects further away

Answer 27

ciliary body relaxes, ligaments tighten and the lens flattens to focus on the object

Question 28

what innervation controls the contraction of the ciliary body

Answer 28

parasympathetic

Question 29

describe the process of seeing objects close

Answer 29

the ciliary body contracts, the ligaments relax, and the lens becomes spherical to focus on the object

Question 30

what are the 3 components of clinically testing the near response reflex

Answer 30

- bilateral pupil constriction - bilateral convergence of eyes to midline - Bilateral relaxation of the lens

Question 31

why are basal tears secreted

Answer 31

corneal health

Question 32

what is the function of basal tears

Answer 32

washed over the cornea during blinking to clear/nourish and hydrate the avascular cornea

Question 33

what enzyme do basal tears contain and what is its function

Answer 33

lysozyme | hydrolyses bacterial cell walls

Question 34

what are reflex tears produced in response to

Answer 34

mechanical or chemical stimulation

Question 35

what are the afferent and efferent limbs involved in reflex tears

Answer 35

afferent - CN V1 to the cornea/conjunctiva | efferent - CN VII parasympathetic axons

Question 36

describe the pathway of CN VII to the lacrimal glands

Answer 36

- enters at the temporal bone - branches off the geniculate ganglion - passes through the medullcranial fossa - into pterygoid canal - pterygopalatine ganglion - sympathetic fibres form the internal carotid join the ganglion - both pass to lacrimal glanf following V1 and V2 fibres