L5 iris and pupil

Question 1

explain more about the iris’s muscles (iris sphincter and iris dilator)

Answer 1

1. sphincter pupillae
   - iris sphincter contracts, dilator muscles dilate, pupil constricts (miosis), innervated by the parasympathetic
2. dilator pupillae
   - iris sphincter dilates, dilator muscle constricts, pupil dilates (mydriasis), innervated by the sympathetic pathway

Question 2

what is the 2 neutral information involved in pupillary control?

Answer 2

afferent : transmission of signals from eye to brain

efferent : transmission of signals from brain to eye

Question 3

what are the administrator types of pupillary reflexes?

Answer 3

1. light (direct and consensual) reflex

2. near reflex

Question 4

describe light reflex

Answer 4

1a. direct reflex
- when we shine line onto the retina, the pupil on the same side will constrict

eg when we shine light onto the right retina, the right pupil constricts. This indicates direct reflex on the right eye

1b. consensual reflex
- when we shine light onto the retina, the opposite side pupil will constrict, indicating left consensual reflex
- this is seen because of the partial crossing of nerve fibers/partial decussation, half of the nasal fibres cross over to the temporal side in the mid-brain

Question 5

describe near reflex

Answer 5

• it is seen when fixation changes from distance to near
• • this is independant of illumination
• near reflex is seen in any illuminations (normal,dim or bright) as long as fixation changes to near

-> pupillary constriction, accommodation and convergence will occur together

pupillary constriction
- action of the iris sphincter muscle

accommodation
- action of the ciliary muscles result in increased focussing power of the lens

convergence
- action of the medial recti muscle

Question 6

describe anisocoria

Answer 6

• the difference in pupil size between 2 eyes
• only seen in efferent pathway defects
• > this is because right brain communicates with only the right side and vice versa for the left brain

-> 2 types: physiological and pathological

Question 7

describe the two types of anisocoria

Answer 7

1. physiological anisocoria
   - congenital (since birth)
   - amount of anisocoria is the same in bright and dim illumination

-> difference in pupil size is the same in dim and bright illumination

2. pathological
   - not congenital (not since birth)
   - acquired due to:
   a. efferent pathway defects (parasympathetic/sympathetic)
   b. pupillary musculature defects (sphincter/dilator)
   - pathological aniscoria is NOT the same in bright and dim illumination

-> difference in pupil size is different in bright and dim illumination

Question 8

what are the steps involved in pupillary examination?

Answer 8

PERRLA & MG

P: pupils (if there is any) 
E: equal (if pupils r equal size) 
R: round (if pupils r round)
R: reacting to light, & 
L: light reflex, chcking fr direct&consensual reflexes
A: accommodation 

MG: marcus gunn pupils

Question 9

describe abnormal pupil responses

Answer 9

-> Light-near dissociation
- seen in efferent pupillary defects
* is abnormal light reflex and normal near reflex
-> for light and dim illumination:
pupil size remains the same in both bright and dim illumination

• > for near illumination:
• ** pupils constrict when fixation changes from distance to near
• pupils do not react to light
  (the pupils do not constrict in bright light neither do they dilate in dim illumination, but they constrict whenever fixation changes from distance to near)

Question 10

describe Marcus-Gunn pupil/ relative afferent pupillary defect (RAPD)

Answer 10

• is an abnormal light reflex and normal near reflex
• > RAPD is not light-near dissociation, only the direct reflex is affected

**afferent defect, no anisocoria
(optic nerve or extensive retinal damage)
- with asymmetric damage in both eyes (damage in eyes are different in each eye)
-> will NOT be seen if both eyes are equally damaged

• seen in optic nerve lesions
• detected with swinging light test