Lec 12: chromatic aberration

Question 1

There are many more optical defects in the eye than simply sphere, cylinder, and prism. what are they?

Answer 1

• correct sphere and cylinder

- correct additional aberrations

Question 2

What kind of optical defects do eyes have?

Answer 2

1. Sphere and cylinder refractive error
2. chromatic aberrations (LCA & TCA)
3. Monochromatic aberrations (Zernike forms)
4. Diffraction (1.22 λ/ d )

Question 3

due entirely to the fact that the watery medium of the eye has a refractive index that varies with wavelength.

Answer 3

Chromatic aberration

Question 4

Non-normal rays are refracted differently because ne varies with wavelength.

Answer 4

dispersion

Question 5

As a result, the angle of refraction varies with what?

Answer 5

wavelength

Question 6

short wavelength is refracted _______ than long wavelength light

Answer 6

more

Question 7

The net effect is a _______________ (i.e., chromatic difference of focus) and _______________ in the point of intersection of isolated rays (chromatic difference of position).

Answer 7

longitudinal shift in focal length and a transverse shift

Question 8

chromatic difference of focus

Answer 8

longitudinal chromatic aberration

Question 9

transverse chromatic aberration

Answer 9

chromatic difference of magnification

Question 10

where is the longitudinal ca?

Answer 10

optical axis

Question 11

where is the transverse ca?

Answer 11

retinal surface

Question 12

Dispersion of water is not constant, but varies by about ____ across visible spectrum

Answer 12

1%

Question 13

high refractive index is associated with short wavelength. what does light do?

Answer 13

light bends more

Question 14

there is variation of power with wavelength in the reduced eye filled with water (T/F)

Answer 14

true

Question 15

0.1 n change is equal to what diopter of refractive error?

Answer 15

13D refractive error

Question 16

difference for prediction from reduced eye

Answer 16

1.76 D

Question 17

difference for best fit data from pts of the real eye

Answer 17

2.1 D

Question 18

Which has bigger difference in D (reduced eye or real eye)?

Answer 18

real eye

Question 19

Luminous efficiency of white light: the narrow sensitivity profile of photoreceptors helps mitigate against what?

Answer 19

against chromatic defocus effects on vision

Question 20

Conclusion of relative luminance vs wavelength

Answer 20

Conclusion: our narrow sensitivity profile of photoreceptors helps mitigate against chromatic defocus effects on vision.

Question 21

what explains why color is not observed easily when viewing a white point source? Our vision is dominated by the central, bright, well focused core.

Answer 21

Narrow spectral width of the luminous efficiency curve

Question 22

If your patient looks at a purple spot and sees a red spot surrounded by a blue halo, you should do what?

Answer 22

prescribe minus lenses b/c we need to move focused retinal plane onto blurry retinal plane

Question 23

Retinal image of white point object will be composed of colored, concentric rings due to what?

Answer 23

chromatic aberrations of the eye.

Question 24

what do we do if short wave is more in focus than long wave?

Answer 24

put plus lens; need to move it forward (cue for eye to accommodate)

Question 25

what wavelength retinal image (relative to the long-wavelength image) is a cue to accommodate?

Answer 25

a higher contrast of the short-wavelength

Question 26

what wave length retinal image (relative to the long-wavelength image) is a cue to relax accommodation?

Answer 26

a lower contrast of the short-wavelength

Question 27

what is LCA?

Answer 27

due entirely to the fact that the watery medium of the eye, like all dieletric media, has a refractive index that varies with wavelength

Question 28

Chromatic difference of magnification (CDM) is what?

Answer 28

a variation in the retinal image size with wavelength.

Question 29

what is z? what is typical z value?

Answer 29

z = distance between nodal point and entrance pupil of eye; 4 mm

Question 30

what is CDM?

Answer 30

0.84%

Question 31

WHAT happens when we increase z? How do we do this?

Answer 31

CDM increases

put pinhole lens (aperture replaces major iris-creates new entrance pupil)–> z will increase –> cdm increases

Question 32

when two eyes are involved, how will u perceive the red and blue?

Answer 32

if pinhole is more temporal: red appears to pop out

if pinhole is more nasal: blue appears to pop out