Talk:Overview of Low Vision

Rough notes from Laura (may be too much technical info, we will see...)

Types of color vision disabilities. Typically a decreased ability to see color or a decreased ability to tell colors apart.
The term "colorblind" is frequently misleading as it seldom means a person sees in greyscale, which is rare.
Cones are the cells that let people perceive color.
Each cone contains a photopigment that is stimulated by blue, red or green wavelengths in the spectrum.
When stimulated, the signals are mixed in the brain and recognized as color.
- Trichromatic = full color vision; all 3 cones
- Dichromatic color vision = entire group of photopigments missing
- Monochromatic = can't distinguish color.
Basically 4 types of color disabilities exist: protanopia, deuteranopia, tritanopia and rod monochromacy.

Absence of L (red) cone: protanopia. Red color waves read as "no signal", or "black". Difficulty distinguishing green–yellow–red. Red, orange and yellow brightness is reduced.
1. Malfunctioning L (red) cone: protanomaly.
Absence of (green) M-cone: deuteranopia. Difficulty distinguishing green–yellow–red. Medium tones of red are likely to be confused with oranges and yellows.
1. Malfunctioning (green) M-cone: deuteranomaly.
Absence of S-cone (blue): tritanopia. Difficulty distinguishing blue-green and yellow-violet.
1. Malfunctioning (blue) S-cones (tritanopialy).
Cones don't work (achromatopsia or monochromacy). Cannot perceive color. Can only distinguish light, dark and some shades of grey. Relies solely on the rods.

Illustrations of how the 4 types would perceive an image along with trichromats. (Aaron Leventhal's NoCoffee vision simulator could be used: https://chrome.google.com/webstore/detail/nocoffee/jjeeggmbnhckmgdhmgdckeigabjfbddl?hl=en-US). Alternatively Ishihara plates could be referenced.

User needs related to color perception are addressed in the following section: