Spectacle Transmission Flashcards
1-4
A-D
to denote color density
as number ascends…_
transmission reduces
high plus or minus lenses have different transmission throughout lens; darker where _
thicker
visible spectrum:
380-760 nm
much UV and IR light doesn’t reach retina; it’s absorbed by:
cornea, aqueous humor, lens, vitreous humor
less than 400 nm is considered:
what end is most harmful:
UV radiation
shorter wavelengths
ocular damage caused by UV:
high burst
a single dose of high level UV radiation
Welders burn
excessive exposure to UV causes:
photokeratitis (snow blindness)
it takes _ hrs after a burn to feel pain
-heals in _ hrs
6
6 to 24
long term low dose UV results in:
cataracts
_ are at risk for retinal problems due to UV
aphakic (macular degeneration)
IOLs are _
UV absorbing
best method to reduce UV related eye disease is:
sunglasses early in life
only lens materially that inherently does not come with UV filter?
can do what?
CR-39
UV dye
good quality polarizing lenses filter _
UV radiation
Do photochromic lenses protect against UV light?
yes - in their darkened state
glare control lenses block _
short blue wavelengths
_ measure UV absorption
photometers
How to test if lens absorbs UV?
place test lens over an unedged plastic photochromic lens and expose to sunlight - if photochromic darkens, test lens does not absorb it all
frame selection for UV:
_ lens area
fits _
_ style
large
close to face
wrap
when UV radiation combines with blue light and IR, causes lens opacification called:
glass blower’s cataracts
sources of IR radiation:
molten substance (glass, metal)
arc lamps
IR lamps
lenses that block IR
NoIO
IREX
transmission for sunglasses is:
15-30%
sunglasses that transmit less than 15% may present problems because of _
reflected glare from back surface (back surface AR fixes this)
according to ANSI standards, sunglasses used for driving should not be darker than:
8%
special purpose 3% transmission may be used for:
rock climbing, beach, skiing
single exposure to ordinary bright light for 2-3 hours caused dark adaptation to start _ minutes later
caused normal night vision to be delayed by _
10
several hours
dark adaptation loss can be prevented with sunglasses that have transmission between:
10-15%
normal 20/20 through glass windshield: _ through 82% transmission pink lenses: _ green tinted windshield: _ together: _
20/32
20/40
20/46
20/60
Does a light tint reduce glare at night? Use what?
no (they do reduce internal reflections)
AR - increase transmission, increase contrast sensitivity
crown glass and plastic transmit _%
92
pink lens benefit?
transmit light uniformly (no color distortion)
reduces glare because it reduces internal reflections
yellow are advocated for _ driving because they enhance contrast
fog/haze, night driving
most common color used in germany, higher absorption in shorter wavelengths like with yellow lenses
brown
lens color that has a transmission curve close to color sensitivity of human eye, good UV and IR too
green
green is a very _ tint
comfortable
most popular color for sun protection
gray
gray offers _ transmission
uniform
best lens color for color vision deficient patients
gray
4 categories for sunglasses
- cosmetic
- general purpose
- very dark
- strongly colored (selective filtration)
color deficient individuals cannot discriminate red and green traffic signals through _ lens color
brown
tinting plastic lenses:
longer dip = _
_ color
darker
uniform
lenses are darker in the upper portion of lens
gradient tinting
_ does not tint at all, all tint is absorbed by scratch coating
polycarb
advantage of color coating lenses:
uniform density regardless of thickness
color coating lenses results in smoothness of its _
transmission curve
Do internally tinted or color coating lenses allow more transmission?
color coating
sunglass wearers can experience reflections on back surface from behind during the day, what would fix this?
back surface AR
reflections on front surface from behind is noticeable at night from _, results in _
bright light source from behind, ghost images
adjustments that can alleviate ghost images: (2)
pantoscopic
faceform
(neither eliminate)
regardless of source, _ reduce ALL reflections
AR coatings
mirrors are applied just like _
AR coatings
mirror coatings _ transmission due to high amount of reflections, what %
reduce (by 15%)
mirrors can be used in conjunction with _ to provide extra protection from intense sunlight
tints
4 types of mirror lenses:
- full mirrors
- gradient mirrors
- double mirrors
- flash coatings (just a hint)
