Lecture 3

Question 1

what gives the iris an opaque appearance?

Answer 1

due to the melanin granules in the epithelium and sometimes the stroma

Question 2

does the iris have optical power?

Answer 2

no

Question 3

what are the 4 important optical roles of the iris?

Answer 3

defines pupil by blocking undesirable light, regulates retinal illuminance, controls depth of field, and aides in controlling retinal blur

Question 4

what makes a brown iris different from blue/green?

Answer 4

brown = melanin granules in stroma and epithelium
blue/green = granules only in epithelium

Question 5

what limits the brown iris transparency?

Answer 5

absorption by pigmentation

Question 6

what inhibits the transparency in the blue iris?

Answer 6

scatter (Rayleigh) by molecules in iris

Question 7

what is the luminance range for the human visual system?

Answer 7

10-log

Question 8

how does the pupil size affect the brightness of the retinal image?

Answer 8

image brightness is proportional to the pupil area (not diameter)

Question 9

how much brighter is an image in an 8mm pupil vs. 2mm pupil?

Answer 9

8mm pupil will pass 16x more light = (8mm)^2/(2mm)^2

Question 10

how much does the pupil contribute to the 10-log luminance range of the eye?

Answer 10

only 1.2 log (rest comes from dark adaptation and photoreceptors)

Question 11

what determines depth of field and depth of focus?

Answer 11

maximum size of acceptable blur at the retina

Question 12

what 3 things does the depth of field ultimately set?

Answer 12

refractive state of the eye measured, focusing optical instruments, accuracy of accommodation system

Question 13

what happens to the depth of field and focus with a small pupil?

Answer 13

they both increases (larger pupil = decreased)

Question 14

what is the depth of field most textbooks use?

Answer 14

1/2 to 1 diopter

Question 15

what is the equation to find depth of field?

Answer 15

2/pupil size

Question 16

what is the clinical significance for depth of field for presbyopes?

Answer 16

increased depth of field with increased ambient light

Question 17

what is a downside for small pupils?

Answer 17

more sensitive to nuclear cataracts

Question 18

what 2 things are compromised by small pupils?

Answer 18

accommodative amplitude and subjective refraction

Question 19

can a pinhole lens correct a refractive error?

Answer 19

no but it ca help make the image more clear

Question 20

what happens to the blur size on the retina with a change in pupil diameter?

Answer 20

a decrease in pupil diameter = decrease in geometric blur size at retina

Question 21

what happens to aberrations with an increase in pupil size?

Answer 21

larger pupil = more aberrations (more retinal blur)

Question 22

will a large slit or a small slit cause more diffraction to occur?

Answer 22

a small slit generates more diffraction

Question 23

what is the image blur size for a point object?

Answer 23

1.22 (wavelength) f/d

Question 24

what happens at a 3mm pupil to diffraction and aberrations?

Answer 24

less than 3mm = diffractions have a larger role

more than 3mm = aberrations have a larger role

Question 25

what is a real pupil?

Answer 25

defines the bundle of light rays that pass from object to retinal image (we cannot see this)

Question 26

what is an entrance pupil?

Answer 26

image of the real pupil formed by cornea (erect, virtual image that resides 0.5mm in front of real pupil)

Question 27

what is an exit pupil?

Answer 27

image of real pupil formed by lens (erect, virtual image that resides 0.1mm behind the real pupil)

Question 28

how much bigger are the entrance and exit pupils compared to real pupil?

Answer 28

entrance pupil = 13% bigger

exit pupil = 3% bigger

Question 29

what type of magnification is given with Snell’s law?

Answer 29

angular magnification

Question 30

which equation is for linear magnification?

Answer 30

mag = h’/h = L’/L = nl’/n’l