TINTS/RADIATION/FILTERS Flashcards
When is radiation damaging
When absorbed by the cells of the adnexa
Cornea absorbs
270nm - 3000nm
Aqueous absorbs
290 - 2700nm
Crystalline lens (old) absorbs
375 - 2500nm
Crystalline lens (young) absorbs
310 - 2500nm
Vitreous absorbs
290 - 1600nm
Transmittance
Light which passes through a medium, after losses by reflection and absorption, represents the Transmittance of the media
Spectral Transmittance
Fraction of luminous flux transmitted by a lens as a proportion of incident light, for a specific wavelength
Spectral Transmittance details
- tells us what a lens transmits for every wavelength
- expressed as %
- transmission curve produced by spectral transmission across a range of wavelengths
Luminous transmission (LTF)
Measures the transmission of a lens over the visual spectrum
LTF details
- considers standard light sources
- illuminant D65
- figure to compare tints
- BS states tints should be stated as LTF
LTF Formula
LTF = luminous flux reaching eye through lens / luminous flux reaching eye without lens
UVB
- 280-315nm
- most dangerous to ocular tissue
- suburn / BCC
- keratitis / snow blindness
UVA
- 315-380nm
- long term exposure absorbed by crystalline lens
- DNA damage/ wrinkles/ cataract
UV exposure
- welding
- physiotherapy
- snow/ sea/ sand reflects high amounts
- delayed symptoms (up to 12 hours)
- itching/ blisters/ lacrimation/ photophobia
IR exposure
- extends around 780-1000nm
- stimulates sensory nerves
- provides awareness
- thermal lesions produce in ocular tissue around 800-1400nm
- heat cataract/ bleaches photoretinal pigment
- causes macula and choroidal lesions
BS EN IS0 8930-3
Transmittance specifications and test methods
BS EN IS0 12312
Eye and face protection, sunglasses for genral use
