Lec 12: chromatic aberration Flashcards
There are many more optical defects in the eye than simply sphere, cylinder, and prism. what are they?
- correct sphere and cylinder
- correct additional aberrations
What kind of optical defects do eyes have?
- Sphere and cylinder refractive error
- chromatic aberrations (LCA & TCA)
- Monochromatic aberrations (Zernike forms)
- Diffraction (1.22 λ/ d )
due entirely to the fact that the watery medium of the eye has a refractive index that varies with wavelength.
Chromatic aberration
Non-normal rays are refracted differently because ne varies with wavelength.
dispersion
As a result, the angle of refraction varies with what?
wavelength
short wavelength is refracted _______ than long wavelength light
more
The net effect is a _______________ (i.e., chromatic difference of focus) and _______________ in the point of intersection of isolated rays (chromatic difference of position).
longitudinal shift in focal length and a transverse shift
chromatic difference of focus
longitudinal chromatic aberration
transverse chromatic aberration
chromatic difference of magnification
where is the longitudinal ca?
optical axis
where is the transverse ca?
retinal surface
Dispersion of water is not constant, but varies by about ____ across visible spectrum
1%
high refractive index is associated with short wavelength. what does light do?
light bends more
there is variation of power with wavelength in the reduced eye filled with water (T/F)
true
0.1 n change is equal to what diopter of refractive error?
13D refractive error
difference for prediction from reduced eye
1.76 D
difference for best fit data from pts of the real eye
2.1 D
Which has bigger difference in D (reduced eye or real eye)?
real eye
Luminous efficiency of white light: the narrow sensitivity profile of photoreceptors helps mitigate against what?
against chromatic defocus effects on vision
Conclusion of relative luminance vs wavelength
Conclusion: our narrow sensitivity profile of photoreceptors helps mitigate against chromatic defocus effects on vision.
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.
Narrow spectral width of the luminous efficiency curve
If your patient looks at a purple spot and sees a red spot surrounded by a blue halo, you should do what?
prescribe minus lenses b/c we need to move focused retinal plane onto blurry retinal plane
Retinal image of white point object will be composed of colored, concentric rings due to what?
chromatic aberrations of the eye.
what do we do if short wave is more in focus than long wave?
put plus lens; need to move it forward (cue for eye to accommodate)
what wavelength retinal image (relative to the long-wavelength image) is a cue to accommodate?
a higher contrast of the short-wavelength
what wave length retinal image (relative to the long-wavelength image) is a cue to relax accommodation?
a lower contrast of the short-wavelength
what is LCA?
due entirely to the fact that the watery medium of the eye, like all dieletric media, has a refractive index that varies with wavelength
Chromatic difference of magnification (CDM) is what?
a variation in the retinal image size with wavelength.
what is z? what is typical z value?
z = distance between nodal point and entrance pupil of eye; 4 mm
what is CDM?
0.84%
WHAT happens when we increase z? How do we do this?
CDM increases
put pinhole lens (aperture replaces major iris-creates new entrance pupil)–> z will increase –> cdm increases
when two eyes are involved, how will u perceive the red and blue?
if pinhole is more temporal: red appears to pop out
if pinhole is more nasal: blue appears to pop out
