Chromatic Aberrations In The Human Eye Flashcards by Sarah Heath

What are the types of monochromatic aberrations

Defocus
Astigmatism
Coma 
Trefoil 
Spherical aberration

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What are the chromatic aberrations

Longitudinal (LCA)

Transverse (TCA)

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What are the two things we care about in LCA

Chromatic difference of power (focus, defocus, blur..)

- chromatic difference of refraction

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What two things do we care about in transverse chromatic aberration (TCA)

Chromatic difference of position

- chromatic difference of magnification

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What is said about the stimulus if red is focused on the retina

It is low stimulus, object far away

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What is said of the stimulus of the blue is in focus

Object is close, high stimulus

-may cue accommodation

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Significance of chromatic defocus (LCA) depends on what

Luminance

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What does the autorefractor measure people

Hyperopic

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What is the LCA average (distance from red to blue)

2.1D

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At what wavelength do people become hyperopic

580nm

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What happens to the refractive error with higher wavelengths

Increases

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What do short wavelengths make people

Myopic

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What do long wavelengths do to people

Make them hyperopic

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The chromatic difference of focus (CDF) reduces retinal image contrast by _____ of defocus

- relatively minor

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What is the amount of defocus in the chromatic difference of defocus equivalent to

The amount of defocus is equivalent to the depth of field of the human eye

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What does the chromatic difference of focus do for vision

Reduces contrast moderately

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Effect of chromatic defocus on VA

Minor effect on the VA

- any attempt to correct would only provide marginal benefit and surface new problems

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The chromatic difference of magnification for two wavelengths of light has what kind of relationship with the axial distance (z) from the pupil to nodal point

Proportional

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What is the equation for the chromatic difference of magnification

Change in mag=z(2D)

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What is the change in mag usually

0.8%

Considered insignificant

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What does the magnitude of the effect depend on

Axial distance Z

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When can magnification be 0

Only if the pupil and nodal point are at the same place

0 axial length

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What is the axial length we look at for magnification

Pupil to nodal point

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When is magnification significant

Looking through optical instrument. 
Depth perception (3D glasses)

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CDM (chromatic difference in mag) and depth perception

Red and blue have different focuse and magnification. -if one eye view through short wavelength light, the visual system may interpret the different sized retinal images as a difference in relative depth resulting in a distorted perception of 3D world

The chromatic difference of position is directly proportional to

- stimulus eccentricity (certain field angle) | - lateral displacement (foveal vision)

How much is the pupil decentered

0.5mm nasally

CDP (chromatic difference of postion) for stimulus eccentricity

For object points off the achromatic axis, the amount of TCA as a function of axial location of pupil z, CD-R, and the angle of eccentricity

What happens when you increase eccentricity to TCA?

Increases it just slightly

Equation for stimulus eccentricity

TCA=(z)sin(e)(2D) Z=axial length E=eccentricity 2=given, LCA

Chromatic difference of position induces ________________ which affect image contrast (visual performance)

Wavelength depends spatial phase shifts

What does chromatic phase shift affect

- defining color | - luminous contrast in the image

CDP (chromatic difference position) for displaced pupil

If the limiting aperture is displaced by amount 'h' from the visual axis, then the magnitude of TCA present at the fovea is h(2D)

What does a 1mm displaced pupil do to TCA

There is 7.2arcmin of TCA

1mm of displacement of external pupil is equivalent to ____ of eccentricity for the naked eye. Both generate same amount of TCA

15 degrees

What is a major limiting factor for foveal vision

Displaced aperture -limitations due to ocular chromatic aberrations may arise due to clinical assessment of visual function using a misaligned optical instrument with respect to the visual axis

Effect of TCA on VA

-the ocular chromatic aberration accounts for most of the acuity loss suffered when viewing through a displaced pupil

The vVA drops from 20/20 to 20/60 when the test instrument is displaced _____ from the visual axis

3mm

What will all points on the retina image suffer

From the combined effect of lCA and TCA

What point on the retina will it not suffer from combined effects of LCA and TCA

The location on the retinal image when eyes achromatic axis intersects with the retina where TCA=0

LCA reduces image contrast how

Blur

TCA reduces image contrast how

By inducing phase shifts

Which reduces image contrast more, LCA or TCA?

TCA

What happens when the pupil is displaced

A large amount of TCA results, causing the image to be spread out horizontally like a tiny rainbow

When the pupil is displaced and you are myopic, what color will be in focused when a white light source is shown

Green

When the pupil is displaced and you are hyperopic, what color will be in focus if a white light source is shown to you

Red

If the pupil is displaced and you are emmetropic, what color will be in focus when you see a white light source

Yellow

What happens to VA if you increase target vergence (increase defocus)

Decreases

What could help lessen the affect of that increased target vergence has on VA?

Corneal inlay

How large is a corneal inlay

1.6mm

What happens if the inlay is displaced even 1-2mm

Dramatic VA decrease

What is a good way to reduce displacement of a corneal inlay

Use perkinje 1 when laying inlay -you will still get chromatic aberration 0use aberrometer and make sure TCA=0 during surgery

A point object emitting two wavelengths of light will produce a double retinal image whihc gives rise to the perception of a double object, a condition called

Chromatic diplopia

Chromatic diplopia is the basis for what

Chromostereopsis

A stereoscopic illusion in which a differently colored object located at the same viewing distance appear to lie at a different distance (3D movies)

Chromostereopsis

________ is an effect of TCA combined with binocular vision

Chromostereopsis

In chromostereopsis, what color appears closer

Red

What is a good example of chromostereopsis?

Stained glass trans illuminated by sunlight

In chromostereopsis, if the pupil is displaced temporally, what color will appear closer

Red

In chromostereopsis, if the pupils are displaced nasally, what color appears closer

Blue

What two things can we fix that will give us the minimum creation to VA

Defocus + astigmatism (lower order aberrations)

What thing that if we could fix, would correct our VA the best

Higher order monochromatic aberrations + chromatic aberrations

When only monochromatic aberrations are corrected, the contrast sensitivity of the eye is improved by a factor of

When only monochromatic and chromatic aberrations are corrected, the contrast sensitivity of the eye is improved by a factor of

3.2 to 5

Optical elements are based on

Abbe number and refractive index

What quantity of light a material disperses

Abbe number

Is it better to have a higher or lower abbe number

Higher

Separation of white light into component elements is referred to as

Chromatic dispersion

Dispersion of water accounts for about _____ across visible spectrum according the water eye model

Variation of power with wavelength is chromatic difference of

Power (focus, blur, defocus) | -LCA

Power of ______ when measuring in object space

Refraction

Power of ____ when measuring on retina

Power

TCA may be specified by ____ for a different wavelength

Angle

True or false, TCA of the human eye does not change over life

True

Change in chromatic berration is determined by _____ of medium

Dispersions | NOT RI

Determine chromatic difference of magnification if axial distance is 0.25

0. 25 X 2 | 0. 50

Changes at different positions induces _____ which affect image contrast

Phase shift TCA

When viewing a trans illuminated stained glass window, if the chromostereopsis makes blue appear close, the pupils re displaced how

Nasally

What does the epsilon in the equation for CDP by eccentric stimulus stand for

Eccentricity =zsin(E)(2.1) Convert to arc min!

Chromatic Aberrations In The Human Eye Flashcards

(79 cards)