20: Pupil Flashcards
where is the sphincter muscle located
in the stroma of the pupillary zone
contraction of sphincter muscle causes
pupil constriction (annular fibers)
the sphincter muscle receives ____ input
parasympathetic
the iris has what kind of surface
a posterior double-epithelial surface
smooth muscle fibers extend into the iris stroma and form the:
dilator muscle
dilator muscle receives ____ input
sympathetic
contraction of the dilator muscle causes
pupil dilation
radial fibers
what is low transmittance important for
to prevent debilitating intraocular scatter
location of the iris aperture vs. the entrance pupil
the entrance pupil is anterior to the iris aperture and is magnified slightly (about 113%)
pupil magnification is the
ratio of entrance pupil diameter to iris aperture diameter (depends on corneal aberration, including distortion)
pupil magnification is ______ for an 8mm pupil (slightly less than paraxial value)
109.5%
where is the pupil center located
about 0.5mm nasal to the optical axis (on average)
how does the shape of the pupil change if it is viewed from an oblique viewing angle?
a circular pupil becomes elliptical from an oblique viewing angle
what is anisocoria
unequal pupil diameters in the two eyes
what percentage of people can have anisocoria and how much of it?
about 17-18% of healthy individuals have anisocoria greater than 0.4 mm
describe the differences in pupil response time to light and dark
the reaction period if longer in dim light and shorter in bright light
pupil diameter changes with age
pupil diameter decreases with age (about 0,04mm per year)
retinal illumination changes as a factor of pupil size
retinal illuminance increases in proportion to the square of pupil radius
_____ pupils allow for greater depth of field
smaller
how does a small pupil increase depth of focus
a small pupil can reduce the blur circle diameter despite the presence of dioptric defocus
how does diffraction become important for small pupils only?
for pupil diameters less than about 2mm, diffraction affects the transfer of high spatial frequencies
the effects of monochromatic aberrations generally _____ with pupil size
increase
the effects of monochromatic aberrations are small for pupil diameters ___ mm or less
3 mm or less
retinal illuminance _____ (increases/decreases) for a smaller pupil
decreases
what does the contrast sensitivity function show for retinal illuminance changes
low spatial frequencies are more robust to changes in retinal illuminance
4 conditions for smaller pupil
- better depth of focus
- more diffraction
- less monochromatic aberration
- lower retinal illuminance
4 conditions for larger pupil
- smaller depth of focus
- less diffraction
- more monochromatic aberration
- higher retinal illuminance
