Topic 5: Iris & Pupil Flashcards
name the transmission of information from Eye > Brain and Brain > Eye
afferent and efferent respectively
what causes pupillary constriction / miosis
contraction of sphincter muscle, shining light onto the retina, changing fixation from distance to near
explain direct reflex
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
explain consensual reflex
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)
explain near reflex
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
explain anisocoria
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
explain steps in pupillary examination (PERRLA MG)
(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
explain light-near dissociation
abnormal light reflex, normal near reflex
possible even if input for near stimulus is different from light stimulus, because efferent pathway is the same
explain marcus gunn pupil
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