Intraocular Scatter 1 Flashcards
When the scattering particles size is about the same size as the wavelength of light
Tyndall scattering (colloidal particle scattering)
What does tyndall scattering act like?
More like rayleigh
When ____________ are about the size of a wavelength wave effects result in tyndall scattering
Transparent particles
Tyndall scattering is _______ dependent scattering (almost)
Wavelength
Scattering profile of tyndall scattering
Scattering in more directions, not just forwards and back
There is no dramatic changes due to the _____ during tyndall scattering
Absorption. More like rayleigh
Tyndall scattering in opal
Tyndall scattering at these in-homogeneities leads to a bluish color in reflected light
What gives blue eyes there blue appearance?
Tyndall scattering in the iris stroma
Why does some of the light scatter back out of the eye in blue eyed people
In the absence of melanin, the translucent stroma scatter some of the light back out of the eye
Tyndall scattering in a blue takes place to a greater extent at the _____ wavelengths and it viewed against the dark background of the iris pigmented epithelium
Shorter
The blue iris is an example of a _________ color, unlike a pigmented color
Structural
Why do albinos have red eyes?
They do not produce melanin. Their eyes color is red because the blood vessels behind the eyes are visible
The incoherent scattering depends on the ________ size
Particles
Is there is a smaller wavelength, what kind of scattering?
Mie
What causes scattering in mie scattering?
Reflection and refraction Caucasus scattering
Direction of scattering mie scattering
Forward
Mie scattering is _______ independent
Wavelength
Example of mie scattering
Whiteness of the clouds
What kind of scattering has particle size equal to the wavelength of light
Tyndall
What causes the scattering in tyndalll
Interior wave effects causes scattering (diffraction)
Direction of scattering in tyndall
Spread light out in more direction
Tyndall scattering is ________ dependent
Wavelength
Examples of tyndall scattering
Halos seen though a fogged up car window
If the particle size is smaller than that of the wavelength, what type of scattering?
Rayleigh
What causes scattering in rayleigh
Dipole re-radiation causes scattering
What direction does rayleigh scattering have?
All directions
What kind of wavelength dependence does rayleigh scattering have?
Stronger dependence at shorter wavelengths (blue) than on the longer wavelength
Example of rayleigh scattering
Blue sky
What kind of scattering is responsible for the sky looking whiter near the sun?
Mie
What scattering scatters roughly equally in all directions
Rayleigh
When reflected and transmitted light are perpendicular in rayleigh scattering gives strong _________
Polarization
Orange sunset is what type of scattering?
Multiple
Green flash at sunset
Red and yellow go above the observer, blue goes below and green goes right to the observer. Must be very clear atmosphere with no pollution.
When the particles are much closer together than the coherence length of the light, constructive and destructive interference occurs between the waves scattered from different particles
Coherent scattering
In coherent scattering, particles are much _______ than the wavelength of the light
Smaller
Each particle acts as a _____ for the coherent scattered waves
Source
Scattered waves propagate _______ and overlap in coherent
Outward
Coherent scattering acts as a
Diffraction grating
Many coherent scattered waves interfere destructively in ______ directions
Most
Many coherent scattered waves interfere constructively in _____ directions
Two
Constructive coherent scattering in 2 directions
- Parallel to incident light (forward scatter)
- refract relative to incident wave (phase shifted)
Light scatter leads to deleterious visual effects like
- glare while night driving
- hindrance from low sun during daytime
- facial recognition problems
- haziness of vision
- color and contrast loss
Sources of ocular scatter
- cornea
- sclera and iris
- lens
- vitreous humor
- retina
Forward scattering (FWS)
Light going into the eye
Backward scattering (BWS)
Light reflecting back from the fundus
Eye is assessed by ______ light scatter, using slit lamp mainly
Backward
______ light scatter is studied in vitro in human donor lenses
Forward
What is BWS used for
Dx
What is FWS used for
Function of vision, human donor lenses
What does the corneal endothelium do
Pumps excess water out of the cornea into the aqueous humor
Reasoned for scattering in cornea
Loses its transparency and takes on grayish appearance, scar tissue on the cornea
The collagen fibers in sclera have ______spacing than the wavelength of light, causing what kind of scattering
Larger
Mie scattering
Due to ___________, sclera appears whitish
Large particle incoherent forward scattering
Sclera thinning
Fibers get smaller and sclera takes on a bluish color due to rayleigh type scattering
Functional effect
Melanin and scleral function
Although the function of sclera is to block the light entering the eye, they are not totally opaque. Light can get through sclera depending on the level of pigmentation and density of the structures generating intraocular scattering
Those without melanin may experience more scattering
______ pigments in the lens scatter more light (forward scatter)
Yellow
Functional effect
Cataract and scattering
Fluid pools
Floaters
Coalescing of collagen fibers causes fluid packets, developing a localized scattering, this causes floating specks and threads
Retina scatters light as much as the ______
Cornea
1/3 bws
How does rental scattering increase
When blood circulation/supply is interrupted, the retinal integrity is damaged, and edema fluid starts collecting in the nerve fiber layer. This increases retinal light scattering turning the area into milky gray (cotton wool spots)
