Topic 5: Iris & Pupil

Question 1

name the transmission of information from Eye > Brain and Brain > Eye

Answer 1

afferent and efferent respectively

Question 2

what causes pupillary constriction / miosis

Answer 2

contraction of sphincter muscle, shining light onto the retina, changing fixation from distance to near

Question 3

explain direct reflex

Answer 3

when light is shone onto the retina, that same side pupil constricts.

eg. light shone on RE retina, RE pupil constricts = direct reflex of RE

Question 4

explain consensual reflex

Answer 4

when light is shone onto the retina, the opposite side pupil ALSO constricts.

eg. shine RE retina, LE pupil ALSO constricts = consensual reflex of LE

due to partial decussation (half of nasal fibres cross over to temporal side in the mid-brain)

Question 5

explain near reflex

Answer 5

pupil constriction in response to changing fixation from distance to near

due to stimulation of CN3

triad reflex: pupillary constriction (iris sphincter muscle), convergence (medial recti muscle), accommodation (action of Ciliary Muscle leading to increased refractive power of lens) happen together

independent of change in illumination

Question 6

explain anisocoria

Answer 6

difference in size between 2 eyes

physiological: congenital, amount of anisocoria same in bright and dim illumination

pathological acquired, amount of anisocoria changes in bright and dim illumination, due to EFFERENT pathway defect + Pupillary muscle defect

Question 7

explain steps in pupillary examination (PERRLA MG)

Answer 7

(1) Pupil - check for presence, if absence there is pathology
(2) Equal - pupils to be measured in bright illumination, if unequal size there is anisocoria (physiological/pathological)
(3) Round - check shape, if irregular there is pathology
(4) Reactive - checking if pupil is capable of constriction and/or dilation. to look out for quality of the reactive speed (fast/sluggish)
(5) Light - checking both RE and LE for direct & consensual light reactions
(6) Accommodation - change fixation from distance to near and observe for near reflex
(7) Marcus Gunn Pupil - check for abnormal direct light reflex but normal consensual reflex with swinging light test

Question 8

explain light-near dissociation

Answer 8

abnormal light reflex, normal near reflex

possible even if input for near stimulus is different from light stimulus, because efferent pathway is the same

Question 9

explain marcus gunn pupil

Answer 9

abnormal direct and normal consensual reflex in affected eye

afferent defect (optic nerve or extensive retinal damage)

can be seen in eyes with perfect vision as long asymmetric damage in both eyes

cannot have anisocoria