Absorptive Lenses Flashcards
ultraviolet range in nm
295nm - 400nm
visible light in nm
400nm- 800nm
infrared light in nm
800nm- 1200nm
UV-C range in nm
100-280 nm
UV-B range in nm
280-315 nm
UV-A range in nm
315-400 nm
cornea absorbs what % of
- incident UVC
- incident UVB
- incident UVA
- UVC: 100%
- UVB: 90%
- 60% incident UVA
the majority of the remaining ____ is absorbed by the lens
UVA
does UVA reach the retina?
small portion of UVA reaches the retina
how much of the high energy visible light (HEV) passes through the cornea and lens?
85-90%
effects of UV absorption of the cornea
- photokeratitis
- pterygia
cataracts from UV-A and UV-B light exposure
cortical cataracts: small, 10% increased risk with higher lifetime sunlight exposure, mechanism not fully understood
cataracts from infrared light exposure
glass blowers cataract
cataracts from high energy microwave
cataracts formed by direct damage to lens fiber cell membranes
retinal light damage is from
UV and HEV (photo thermal, photomechanical, photochemical)
what type of light is related to macular degeneration?
high energy visible light
how can high energy visible light causes macular degeneration?
- short wavelength and blue light cause significant oxidative stress to the RPE
- need further studies and clinical trials to understand fully
3 things infrared radiation
- absorption of high energy IR radiation causes vibrational changes in molecules
- increased temperature on tissue causes denaturation of proteins
- results in loss of function of proteins and enzymes critical to metabolic processes
effects of infrared radiation on cornea, iris, lens, retina
- cornea: corneal burns
- iris: de-pigmentation & atrophy
- lens: glass blower’s cataract
- retina: burns
total light transmission through a lens=
incident light (I) - (reflection + absorption)
medications causing increase sensitivity
- tetracycline
- sulfa drugs
- birth control
- diuretics
- tranquilizers
protection from UV can be from:
absorptive- metal oxide
or reflective- reflective coating
discomfort glare causes:
discomfort but does not affect visual performance
disability glare (Veiling glare)
decrease in contrast causing decrease visibility or resolution such as cataracts, UV absorption by the lens, and cornea scarring
dazzling glare can cause
photophobia
how do glare control lenses work?
block short wavelengths to increase contrast
disadvantages of glare control lenses?
may have an effect on color vision, depending on amount of visible spectrum that is absorbed by the lens
glass photochromic lens contain
silver halide, breaks into silver and halogen when activated by UV, rebinds to silver after exposure to UV stopped
plastic photochromic lenses contain
indolino spiroazines (ISN), this material penetrates the lens surface at about 150 microns, when activated ISN changes structure and darkens- reduces transmittance
what does AR coating reduce and increase?
reduces reflection
increases light transmission through the lens
the ___ the index, the more light is reflected off the surfaces and therefore the less light transmitted
higher
labert’s law of absorption
same % of light is absorbed regardless of intensity of incident light through homogenous substance
the intensity of transmitted light varies exponentially as a function of
the length of the light path in the absorbing media
