Session 12 Flashcards
(24 cards)
Characteristics of UVA? 2
315nm - 380nm,
Least harmful of the three
Characteristics of UVB? 2
290nm - 315nm
Shorter wavelengths and higher energy than UVA.
What can UVA cause? 1
Causes-
skin to tan
What can UVB cause? 4
Causes -
sunburn
photokeratitis
cataracts
retinal lesions
Characteristics of UVC? 2
200nm - 290nm
Higher in energy compared to UVA and UVB but is effectively filtered out by Earth’s ozone layer.
What is a normal transmission for sun lenses?
Between 15% and 30%
What happens if the lens transmits more than 30%?
May not help enough in full sunlight
What happens if the lens transmits less than 15%?
May cause problems with reflected glare from the back surface.
Any colour tint affects your visual acuity T/F
Can you wear sunglasses/Tint for Night Driving?
True
No- advise AR instead + Dry eye drops if AR still ‘does not’ work.
What are the 4 categories of Sunglass Tints?
Cosmetic - more oriented for fashion or indoor lighting (headache tint etc) Grade1
General Purpose - Most common - Grade 1+2
Very dark special purpose - Intense light situations- Less than 15%ltf
Strongly coloured special purpose - filters certain spectral colors more heavily than others.
What is an ideal tint? 5
-Reduces intensity of sunlight
- Eliminates parts of the optical spectrum that are hazardous + not required for vision.
-Provides enough protection so px dark adaption + night vision are preserved at night
-Maintains normal colour vision - so can distinguish traffic lights.
- Resist impact + scratching - minimum care.
What does a color-defective individual lack?
Lack in one of the three different types of retinal cones.
Does an AR coating added to a tint change the LTF of the tint?
Yes, it will transmit more light so it will be lighter
Where is the tint darkest in a High Minus rx (sph)?
Darkest in the edges, lightest in the middle.
Where is the tint darkest in a High Plus rx (sph)?
Darkest in the middle, lightest in the edges
Where is the tint darkest in a plano/high minus rx (sphcyl) rx?
Lighter along the lowered powered meridian, darkest along the strongest powered meridian
How does changing the tint help colour-defective?
The filter used selectively absorbs certain colors but not others. This changes the intensity of those colors, meaning the px can use light intensity cues to tell the colors apart.
What are negative effects of using color defective tints? 2
Colors which were once distinguishable may now be confused when viewed through the filter.
Difference between the two eyes can cause moving objects to appear wrongly located as to how far away they are.
What is a photochromatic lens?
A lens which changes color when exposed to UV
Name 4 considerations with Photochromatic lenses?
-Plastic photochromatic wear out. Glass photochromatic do not lighten in their clear state.
-The time is takes to change colour depends on how long overall they have been worn outside.
-The more the lens is worn outside the quicker it wears out.
-Do not replace just one lens as they age differently.
Which wavelengths are invisble to the human eye?
Ultraviolet (UV)
Infrared (IR)
Between which nm does UV. Visible light and Infrared sit on the spectrum.
UV - 200nm-380nm
VL - 380nm-750nm
IR - 750 onwards
What does ROY G BIV stand for?
Red
Orange
Yellow
Green
Blue
Indigo
Violet
What is the longest and shortest visible wavelength?
Red - longest
Violet - shortest
