Flashcards in The pupil response 1 Deck (43):
What happens in low light level?
Mydriasis - dilation of the pupil in low light level
What is average dilation of pupil?
What happens in bright light level?
Miosis - constriction of the pupil in bright light level
What is average constricted pupil size?
How are pupils size determined?
What happens to pupils as we get older?
Constricted pupil so harder at night to read
what do you call large and small pupil sizes/
microcoria - small
What does genetic factors influence?
Resting pupil size
What is the resting pupil size of males>/
What is the resting pupil size in females?
What is the resting pupil size in children?
What was used to dilate pupil?
Why did womens use atropine?
Make eyes look larger and make them look younger
What happens to pupil in very bright light for long time?
in 200ms pupil gets smaller
takes 2 half second to constrict fully
as light levels get lower pupil response takes longer and constricts less
What is hippus?
The pupil oscillates around average steady state
What is the function of pupil?
To regulate the amount of light entering the eye
What is the difference between fully constricted and fully dilated pupil?
How much does fully dilated and fully constricted pupil alter the light entering the eye bye?
1.2 log units
What does constriction do?
Increases image quality by increasing depth of focus
and reduce amount of spherical aberrations
How can you reduce spherical aberrations?
By closing the pupil- make smaller and cut out any peripheral rays
How does the traid improve image quality? (3)
Accommodation focuses the object
convergence puts the image on fovea
pupil constriction increases depth of field
What does human pupil respond to?
Changes in illuminance
viewing near objects
cortical influences - girls
What does the iris contain?
Two smooth muscles - dilator and sphincter muscles
What is the orientation of the iris muscles?
sphincter- circular muscles
dilator - runs radially
Where is dilator muscle?
>Close to ris pigmented double epithelium (myoepithelium)
What is the dilator muscle innervated by ?
Sympathetic branch of autonomic nervous system
Where is the sphincter muscle?
separated from iris pigmented epithelium
What innervates the sphincter muscle?
Innervated by the parasympathetic branch of the autonomic nervous system
How do pupils respond to in animals without rods and cones?
Mice can also respond to light even without photoreceptors because they have melanopsin that contain retinal ganglion cells that respond in the same way
What is the initial stage of pupil constriction?
light absorbed by retinal photoreceptors
>rods and cones - lower intensity
>melanopsin containing retinal ganglion cells - high light levels
>ganglion cells leave retina and stimulate ganglion cells in optic nerve
What happens to pathway after optic nerve?
To the optic chiasm- decussation- project axons into thE LGN - synapse to optic radiation in visual cortex and results to conscious vision
Not all output goes to visual cortex where does it go?
not all vision is conscious
retinal projection to the OPN (bilateral ) and comes from both eyes
What is OPN?
Olivary Pretactal nuclei
What happens after OPN?
Fibres go directly to the ipsilateral Edingher Westphal nucleus and also to contralateral EWN to mediate consensual response vai the posterior commisure
Explain sensory limb of reflex ARC?
>Light absorbed by photoreceptors(rods, cones, melanopsin ganglion cells)
>activity in the ON
partial decussation at the chiasm
>Projection to OPN
Bilateral Projection to EWN
what is the motor innervation of the iris muscles?
Autonomic nervous system
what is the difference between sympathetic and parasympathetic ganglia?
Sympathetic ganglia are near spinal chord
Parasympathetic ganglia are located by effector
What is the sensory pathway of pupil constriction?
>Bilateral projection to OPN olivary pretectal nuclei from the retina
>fibres to EWN of both sides
What is the motor pathway of pupil constriction?
Preganglionic parasympathetic fibres travel from the EWN within the 3rd nerve to the ciliary ganglion
Postganglionic fibres innervate the iris sphincter muscle within short ciliary nerves
How do ciliary ganglion cells synapse ?
Ach as neurontransmittors
What does Ach bind to?
Where do parasympathetic fibres arise from?
Parasympathetic fibres mediating pupillary response arise in the EWN