Intraocular Light Scatter II Flashcards
What are the two refractive surfaces of the eye?
Cornea and lens
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
What parts of the eye cause forward scattering?
Cornea, sclera and iris, lens, vitreous humor
What parts of the eye cause backward scattering?
Retina
This gives us access to understand the function of the eye
What does scleral thinning cause?
Bluish appearance due to rayleigh scattering
Corneal light scattering is _______ for all healthy eyes, and for all ages
Identical (constant)
Corneal transmittance is _________ dependent
Wavelength
Rayleigh scattering
When the wavelength increases, the corneal transmittance _________
Increases
Contact lens wearers experience a _______________
Significantly higher light scatter
On average, contact lens scatter is ___________ higher than spectacle wearers
0.22 log units
Corneal light scatter may increase __________
Post laser refractive surgery
Light scatter in the cornea
- constant in all healthy eyes
- wavelength dependent
- increases with contacts and corrective surgery
For radial keratotomy (RK) mean stray light increases by a factor of ______ in eyes with 4mm pupil and a factor of _________for 8mm pupil.
1.4
2 (0.3 log units)
Photorefractice keratotomy (PRK) does what for light scattering in the cornea?
Corneal backscattering of light, which correlates with visible haze, is significantly stronger after PRK
Laser assisted in situ keratomileusis (LASIK) does what for corneal light scatter?
Epithelial ingrowth after LASIK can cause an increase in straylight
Corneal refractive therapy (CRT) and corneal light scatter
Reported decreased scatter in the follow ups
Which refractive procedure reduces decreased scatter in the cornea?
CRT
What does a pigmented iris do to scattering?
Decreases it
As angle of scatter increases, scatter ________ in blue eyes a lot
Increases
Are the scare and iris opaque?
Not totally, some pigment is here as well as in the iris
What do the sclera and iris due since they do have pigment
Diffusely transmit long wavelengths due to the color of pigments in the scleral wall and iris
For a dark brown eye of pigmented individuals, transmission is lower by _________
Two orders of magnitude
The amount of scatterin/stray light in the eye depends also on ________
Pigmentation of the fundus
Fundus has a stronger reflectance of __________ wavelengths due to the pigments and the blood
Longer (red)
Blue eyes cause greater what?
Back scattering of light from fundus and more light transmission through the eye wall
What pupil size has the highest scatter?
2-3 mm
What happens to scatter in pupils with 4-10mm pupils?
Scatter remains the same
Light scattering by the crystalline lens and age
Increases significantly with age and much higher for cataracts
- increases by 2x by age of 65
- increases by 3x by age 77
Results 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
Glistening
What kind of lens has less scatter than a normal healthy eye
Monofocal
What does glistening cause
Stronger glare, especially when driving
What does scatter reduce?
-contrast and VA
Introduced IOLS to reduce the amount of blue light transmission in the eye
Blue light blocker
Light scatter is stronger with _____
Blue
Benefits of blue light blocker
- drastically reduces light scatter
- blocks blue iChat harmful to retina
- reduce aberrations of the eye
- do not affect VA, CS, and color vision
What are some potential side effects of reduction in blue light?
Color vision disturbance
Decreased scoptopic sensitivity
-sleep-wake timing disruption
Effects of light scattering: cornea
- constant
- forward scattering
Effects of light scattering: sclera and iris
- pigmentation
- diffuse transmission of red
Effects of light scattering: lens
- forward light scattering
- age and cataract dependent
Effect of light scattering: vitreous
- forward scattering
- age
Effect of light scattering: retina
- backward scattering
- pigmentation
- fundus reflectance
Radiation of sharp needles of light that is perceived subjectively around a bright point light source that originates from light scattering by small particles
Ciliary corona
Color banded, much like the rainbow, perceived surrounding a bright spot of light at a mean distance of 3 degree radius.
Lenticular halo
Originates from the fibrous structure of the eye lens
Lenticular halo
The lens fibers form a diffraction grating, arranged in a circular fashion, much like the spokes of a wagon wheel
Lenticular halo
Appears only for larger pupil sizes, depending on the subject
Lenticular halo
