Scattering Flashcards
- Scattering of light is caused due to the in-homogeneities in a medium
- in-homogeneities = _______
particles
Two MAIN types of scattering
Incoherent
Coherent
CONDITIONS for Incoherent Scattering:
1
2
white light
particles far apart
Incoherent scattering depends on :
size of particles
distance btw particles
strenght of interaction:- refractive index
absorption strength
Mie scattering, Tyndale scattering, or Rayleigh scattering?
particle size > wavelength of light
M
Mie scattering, Tyndale scattering, or Rayleigh scattering?
particle size = wavelength of light
T
Mie scattering, Tyndale scattering, or Rayleigh scattering?
particle size < wavelength of light
R
Mie scattering, Tyndale scattering, or Rayleigh scattering?
• reflection & refraction
causes scattering
M
Mie scattering, Tyndale scattering, or Rayleigh scattering?
Example: halos seen through
a fogged up car window
T
Mie scattering, Tyndale scattering, or Rayleigh scattering?
• forward direction scattering
M
Mie scattering, Tyndale scattering, or Rayleigh scattering?
dipole re-radiation causes
scattering
R
Mie scattering, Tyndale scattering, or Rayleigh scattering?
stronger dependence at
shorter wavelength (blue)
than on the longer
wavelength
R
Mie scattering, Tyndale scattering, or Rayleigh scattering?
spread light out in more
direction
T
Mie scattering, Tyndale scattering, or Rayleigh scattering?
wavelength independent
M
Mie scattering, Tyndale scattering, or Rayleigh scattering?
• interior wave effects causes
scattering (diffraction)
T
Mie scattering, Tyndale scattering, or Rayleigh scattering?
Examples: Blueness of the sky
R
Mie scattering, Tyndale scattering, or Rayleigh scattering?
wavelength dependent
T
Mie scattering, Tyndale scattering, or Rayleigh scattering?
Example: whiteness of the
clouds
M
Mie scattering, Tyndale scattering, or Rayleigh scattering?
isotropic in direction (all)
scattering profile shows forward and backward scatter
R
_________Scattering is an elastic scattering,
as the scattered photons’ energy do not
change
Rayleigh
Inelastic scattering of particles is called
______ Scattering.
Raman
________ Scattering theory applies for particles both absorb and scatter.
Mie
- Techniques based on scattering theory are used in several studies in the understanding of optical
properties of biological tissues like skin, brain, breast, bone, other soft tissues, other fibrous tissues and
fatty tissues, and even blood cell
Mie
The bluer the light the more the light_______
and the larger the area of
________
scatters
glare
Mie scattering produces ______ scattered light
unpolarized
Rayleigh : when reflected and transmitted light are perpendicular , get strong _________
polarization
In 1882, _________published Le Rayon Verte – the Green Ray – in which he
dreamed up an old Scottish legend that says
anyone who sees a green flash will never
again make a misstep in matters of the heart.
Jules Verne
Coherent scattering: When the particles are
___________
than the coherence length of the light,
________and _______interference occurs
between the waves scattered from different
particles
much closer together
constructive and destructive
Coherent scattering:
Particles much_____ than the wavelength of the light
• Each particles acts as a ________ for the coherent
scattered waves
• Scattered waves propagate ______ and overlap.
• Acts as ‘diffraction ______
smaller
source
outward
grating
Many coherent scattered waves interfere…
______ in most directions
•________ in two directions
• _____to incident light (forwardscatter)
• Refract _______ to incident wave
(phase shifted)
• Destructively
Constructively
Parallel
relative
Intraocular Light scatter: leads to deleterious visual effects, like • Glare while \_\_\_\_\_\_\_\_\_\_ • Hindrance from \_\_\_\_\_\_\_ during daytime • \_\_\_\_\_\_\_recognition problems • \_\_\_\_\_\_\_of vision • Color and contrast \_\_\_\_\_
night driving
low sun
Facial
Haziness
loss
Light going into the
eye?
• Forward scatter (FWS) –
Light reflecting
back from the fundus?
• Backward scatter (BWS) – Light reflecting
back from the fundus
Small protein particles (α-crystallin) and rough
surface reflectance dominate ________light
scattering
• Whereas, large sized protein particles
dominate________ scattering.
backward
forward
____________consists of Collagen Fibrils (parallel
bundles) which are less than wavelength of the light.
• Incomplete destructive interference causes about 10%
scattering in cornea.
• Corneal scattering helps in slit-lamp examination of the
cornea.
Corneal stroma
The Collagen fibers (random order) in _____have larger
spacing than the wavelength of light.
• Due to large particle incoherent forward scattering, ________
appears whitish.
sclera
sclera
Case: ________ Fibers get smaller and sclera takes
on a bluish due to Rayleigh-type scattering.
Scleral thinning.
:
• Yellow pigments in the lens scatter more light (forward
scatter).
• Cataract is formed when protein in the lens clumps
together forming fluid pools causing additional
scattering.
• Cataract formation degrades vision by scattering. The
amount of scatter increases with the cataract growth.
Crystalline lens
• With the coalescing of ‘collagen fibers’ in _______due to
aging causes fluid packets and thereby developing a
localized scattering.
• This causes patients to see floating specks and threads.
Vitreous humor
________ scatters light as much as cornea.
• When blood circulation/supply is interrupted, the ______
integrity is damaged, and edema fluid starts collecting in
the nerve fiber layer. This increases______light scattering
turning the area into milky gray (cotton wool spots).
retina
retinal
retinal
Sources of Ocular scattering:
5:
Sources of Ocular scattering:
- Cornea
- Sclera and Iris
- Lens
- Vitreous humor
- Retina
\_\_\_\_\_\_\_\_\_\_ scattering is identical for all healthy eyes, and for all ages. (Constant)+
Corneal light
__________ wearers experience a significantly higher light scatter.*
Contact lens
Corneal light scatter may increase after _____________
laser refractive surgery
surgery type?
– Mean stray light increase by a factor of 1.4 in eyes with 4 mm
pupil and a factor of 2 (0.3 log units) for 8mm pupil.
Radial Keratotomy (RK)*
surgery type? –corneal backscattering of light, which correlates with
visible haze, is significantly stronger after _____
•
• Photorefractive keratotomy (PRK)*
surgery type?– Epithelial ingrowth after ________can cause an
increase in straylight.
•
Laser-assisted in situ keratomileusis (LASIK)*
surgery type? - Reported decreased
scatter in the follow ups.
Corneal Refractive Therapy (Orthokeratology or Corneal reshaping)*
The amount of scattering/stray light in the eye depends also on the pigmentation in the
_________
fundus.
• Sclera and iris are not totally opaque.They diffusely transmit long wavelengths due to the________ in the scleral
wall and iris.
color of the pigments
For a light-blue eye effective transmission of the iris was___%for red and ___% for green
light. Also the eyewall around the iris transmits a significant amount of light.
1%
0.2
Fundus has stronger reflectance of ____ wavelength ____ due to the pigments, and
also the blood.
• Blue eyes, blue-green eyes causes greater________ of light from fundus and
more light transmission through the eye walls.
longer
red
back scattering
For the dark-brown eyes of pigmented individuals transmission is lower by____orders
of magnitude.*
Dark brown eye has abundant melanin pigments which absorbs strongest at ______
wavelength.#
two
shorter
For natural pupils (between
2 and 7 mm diameter),
scatter _______depends on
pupil diameter
weakly
Light scatter by \_\_\_\_\_\_\_\_\_\_\_\_\_ increases significantly with age and much more higher for cataract eyes
crystalline lens
___________ are the result of water absorption and
subsequent phase separation within the IOL matrix and
are clinically observed in almost all types of IOL material,
including hydrophobic and hydrophilic acrylics,
silicone, and PMMA.
Glistenings
:
Radiation of sharp needles of light that is
perceived subjectively around a bright point light
source.
• Originates from light scattering by small particles.
Ciliary Corona
• The ________ is a colored band, much like the rainbow,
perceived surrounding a bright spot of light at a mean
distance of 3° radius.
• it originates from the fibrous structure of the eye lens.
• the lens fibers form a diffraction grating, arranged in a
circular fashion, much like the spokes of a wagon wheel.
• the_______ appears only for______pupil sizes,
depending on the subject
lenticular halo
lenticular halo
larger
: are introduced
IOLs to reduce the amount of blue
light transmission in the eye (Natural
Chromophore).
blue light blocker*
blue light blocker benefits
Drastically reduces the light scatter (see below) • Blocks Blue light harmful to retina • Reduce the effect of chromatic aberrations of the eye. • Do not affect VA, CS, & Color vision
blue light blocker side effects
Potential side effects of a reduction in blue-light
transmission include color-vision disturbance,
decreased scotopic sensitivity (which can lead
to poorer performance in dim lighting conditions),
and sleep–wake timing disruption.
