*Topic 5: iris and pupil

Question 1

what are the 3 types of pupillary reflexes?

Answer 1

1. Direct reflex
2. consensual reflex
3. near reflex

Question 2

what is direct reflex?

Answer 2

when light is shined onto retina, pupil on the side will constrict (e.g right retina–right pupil constrict)

Question 3

what is consensual reflex? why does consensual reflex happen?

Answer 3

when light is shined onto retina, pupil on the opposite side will constrict (e.g right retina–left pupil constrict)

Due to partial crossing of nerve fibres (partial decussation)
1/2 of retinal nerve fibres (nasal fibres) cross over to temporal side in mid brain)

Question 4

what is near reflex? what are the 3 processes that occur during near reflex?

Answer 4

near reflex occurs when we change fixation from distance to near. At near, both pupils will constrict.
***near reflex is independent of change in illumination, will occur regardless of illumination settings

3 processes that occur together (triad reflex)

1. pupillary constriction (contraction of sphincter muscle)
2. accommodation (contraction of ciliary muscles and relaxation of susp. ligaments result in increasing focusing power in lens)
3. convergence (action of medial recti muscle cause eyes to converge)

Question 5

what is the difference between afferent and efferent pathways?

Answer 5

afferent: transmission of signals from eye to brain
efferent: transmission of from brain to eye

!! remember A=Eye

Question 6

what is anisocoria? what are the 2 types of anisocoria?

Answer 6

it is the difference in pupil size between 2 eyes

physiological (ppl born with it, rare only 15%) and pathological (acquired)

Question 7

what are the characteristics of physiological anisocoria?

Answer 7

1. present since birth
2. amount of anisocoria in bright and dim illumination is the same
   * *3. difference in pupil size is the same in bright and dim !! bc fellow pupil still constricts!

Question 8

what are the characteristics of pathological anisocoria?

Answer 8

it is acquired due to:
1. efferent pathway defects (brain to eye, can be sym or parasym)
2. pupillary muscle defect (sphincter/dilator)
3. difference in pupil size is different in bright
and dim!! bc the fellow pupil does not constrict at all!

Question 9

what is miosis? what muscle causes miosis and what pathway is it mediated by?

Answer 9

it is pupillary constriction. it is caused by the contraction of the sphincter muscle and mediated by the parasympathetic pathway

Question 10

what are some factors that cause miosis?

Answer 10

1. light shining onto retina

2. change of fixation from dist to near

Question 11

what are the steps involved in pupillary evaluation ?

Answer 11

PERRLA MG

1. pupils
2. equal
3. round
4. reacting to light
5. light reflex
6. accommodation
7. marcus gunn

Question 12

What is Marcus Gunn pupil (RAPD)? what causes the defect?

Answer 12

It is the relative afferent pupillary defect and it is caused by:

1. optic nerve/extensive retinal damage
2. asymmetric damage (different severity) in both eyes

Question 13

How is MG detected? what is the reflex detected?

Answer 13

It is detected using the swinging light test

reflex detected will be abnormal direct and normal consensual reflex in affected eye

Question 14

why cant a px have both MG and anisocoria?

Answer 14

Anisocoria is a efferent pathway defect while MG is an afferent pathway defect.
Anisocoria is diff pupil size but MG has abnormal direct and normal consensual reflex

Question 15

what causes light near dissociation? what reflex is observed?

Answer 15

the input for near stimulus is different from light stimulus

Abnormal light reflex but normal near reflex is seen

Question 16

what happens during light near dissociation reflexes?

Answer 16

the pupils do not react to light
-do not constrict in bright light, neither do they dilate in dim illumination (pupil size will remain the same)

however they constrict when fixating from distant to near