20: Pupil

Question 1

where is the sphincter muscle located

Answer 1

in the stroma of the pupillary zone

Question 2

contraction of sphincter muscle causes

Answer 2

pupil constriction 
(annular fibers)

Question 3

the sphincter muscle receives ____ input

Answer 3

parasympathetic

Question 4

the iris has what kind of surface

Answer 4

a posterior double-epithelial surface

Question 5

smooth muscle fibers extend into the iris stroma and form the:

Answer 5

dilator muscle

Question 6

dilator muscle receives ____ input

Answer 6

sympathetic

Question 7

contraction of the dilator muscle causes

Answer 7

pupil dilation

radial fibers

Question 8

what is low transmittance important for

Answer 8

to prevent debilitating intraocular scatter

Question 9

location of the iris aperture vs. the entrance pupil

Answer 9

the entrance pupil is anterior to the iris aperture and is magnified slightly (about 113%)

Question 10

pupil magnification is the

Answer 10

ratio of entrance pupil diameter to iris aperture diameter (depends on corneal aberration, including distortion)

Question 11

pupil magnification is ______ for an 8mm pupil (slightly less than paraxial value)

Answer 11

109.5%

Question 12

where is the pupil center located

Answer 12

about 0.5mm nasal to the optical axis (on average)

Question 13

how does the shape of the pupil change if it is viewed from an oblique viewing angle?

Answer 13

a circular pupil becomes elliptical from an oblique viewing angle

Question 14

what is anisocoria

Answer 14

unequal pupil diameters in the two eyes

Question 15

what percentage of people can have anisocoria and how much of it?

Answer 15

about 17-18% of healthy individuals have anisocoria greater than 0.4 mm

Question 16

describe the differences in pupil response time to light and dark

Answer 16

the reaction period if longer in dim light and shorter in bright light

Question 17

pupil diameter changes with age

Answer 17

pupil diameter decreases with age (about 0,04mm per year)

Question 18

retinal illumination changes as a factor of pupil size

Answer 18

retinal illuminance increases in proportion to the square of pupil radius

Question 19

_____ pupils allow for greater depth of field

Answer 19

smaller

Question 20

how does a small pupil increase depth of focus

Answer 20

a small pupil can reduce the blur circle diameter despite the presence of dioptric defocus

Question 21

how does diffraction become important for small pupils only?

Answer 21

for pupil diameters less than about 2mm, diffraction affects the transfer of high spatial frequencies

Question 22

the effects of monochromatic aberrations generally _____ with pupil size

Answer 22

increase

Question 23

the effects of monochromatic aberrations are small for pupil diameters ___ mm or less

Answer 23

3 mm or less

Question 24

retinal illuminance _____ (increases/decreases) for a smaller pupil

Answer 24

decreases

Question 25

what does the contrast sensitivity function show for retinal illuminance changes

Answer 25

low spatial frequencies are more robust to changes in retinal illuminance

Question 26

4 conditions for smaller pupil

Answer 26

1. better depth of focus
2. more diffraction
3. less monochromatic aberration
4. lower retinal illuminance

Question 27

4 conditions for larger pupil

Answer 27

1. smaller depth of focus
2. less diffraction
3. more monochromatic aberration
4. higher retinal illuminance