7. Anatomy of the pupillary pathways and reactions.

Question 1

what are the functions of the pupil ?

Answer 1

increases the depth of focus

amount of light entering the eye

allows the aqueous humour from the posterior to the anterior chamber

Question 2

what is the size of the pupil determined by ?

Answer 2

intrinsics eye muscles

dilator muscle of the iris radial muscle- sympathetic innervation - mydriasis

sphincter muscle circular of the iris - parasympathetic innervation - miosis

Question 3

what are the two reflexes in which pupils are involved ?

Answer 3

light pointed towards the eye - pupil constricts

when it is dark - the pupil dilates

Question 4

why does the pupil appear black ?

Answer 4

light rays entering th pupil are absorbed by the tissues - and mostly miss exiting the narrow pupil

Question 5

what innervates the dilator muscles of the iris ?

Answer 5

sympathetic nervous system of the superior cervical ganglion

3 neurones
first order neurones - starts from posterolateral hypothalamus
run to intermediolateral cell column

2nd order neurone axons travel along the ventral root of C8-TH2
go tot he superior cervical ganglion synapse with third order neurone

3) third order postganglionic neurone
axons join the ophthalmic division of trigeminal nerve
eneter cilliary ganglion with no synapses there and reach the dilator muscle as long colliery nerves

Question 6

what is the parasympathetic nervous system of the sphincter muscles ?

Answer 6

located in the brain stem and spinal cord S2-S4
Edinger westphal nucleus - preganglionic fibres run within oculomotor nerve - synapse at colliery ganglion
from colliery ganglion post ganglionic short ciliary nerves supply the colliery muscle of the pupillary sphincter

Question 7

both pupils constrict even if the light is only pointed towards one eye why ?

Answer 7

the neurone carrying the sensory impulse from the eye synopsis with the two neurones in the EDinger westfal nucleus

and from there the signal is transmitted to the pretecal nucleus in the midbrain - and then from here motor impulses are sent to contract both eyes

Question 8

at what size of the pupil is the best retinal image obtained ?

Answer 8

2.4mm- aberration and diffraction balanced