color vision anomalies Flashcards
dichromat
2 color pigments
anomalous trichromat
abnormally shifted 3 color pigments
principle of univariance
once a photoreceptor absorbs a wavelength of light, all information about the wavelength is lost
a single PR cannot determine a color, color discrimination is based on the relative response of all 3 cone photoreceptors
protanamalous trichromat
the L cone (red) spectrum is shifted towards shorter wavelengths, meaning the eye is less sensitive to longer wavelengths (red). As a result, red, orange, and green all look similar and appear greener than how they appear to a normal trichromat. Reds will appear dimmer (similar to a protanope), but the effect is less pronounced. Protanomalous trichrtomats are described as “red weak”
deuteranomalous trichromat
the M cone (chlorolabe) spectrum is shifted towards longer wavelengths, meaning the eye is less sensitive to shorter wavelengths (green). As a result, red, orange, and green all look similar and will appear more red than how they appear to a normal trichromat. Deuteranomalous trichromats are described as being green weak
tritanomaly
the s cone spectrum is shifted towards longer wavelengths, meaning one eye is less sensitive to shorter wavelengths. This condition is very rare compared to red/green deficiencies
protanopes
missing the erythrolabe photopigment (L). They will confuse red, orange, yellow, and green because there is no overlap between the absorption spectra of the remaining S and M cones for those wavelengths of light. Reddish hues are also seen as very dim (almost gray) because of the poor sensitivity of the M cones to longer wavelengths of light. Colors that contain a mixture of red and another color (purple=red + blue), will be indistinguishable from the other color (purple will look like pure blue)
deuteranopes
missing the chlorolabe photopigment (M). similar to protanopes, they will confuse red, orange, yellow, and green because there is minimal overlap between the absorption spectra of the remaining S and L cones for those wavelengths of light (only L cones respond to longer wavelengths). In contrast to protanopes, deuteranopes do NOT have a noticeable dimming of red hues because the L cones are more sensitive to longer wavelengths of light
tritanopes
missing the cyanolabe photopigment (S). They tend to confuse blues and yellows because there is minimal overlap between the absorption spectra of the remaining M and L cones for those wavelengths of light (only M cones respond to shorter wavelengths of light
monochromatism
rare condition characterized by only one cone type or only rod photoreceptors. These patients cannot distinguish colors
normal on the Nagel Anomaloscope
17 brightness
45 mixture
protanopes and Nagel Anomaloscope
darken test brightness with pure red d/t dimming effect at pure 0
test field: 0-73
deuteranomaly and nagel anomaloscope
adds 546nm-closer to 0 d/t green weak
test field <45
protanomaly and nagel anomaloscope
adds more 670nm; closer to 73 d/t red weak
test field>45
deuteranopes
test field: 0-73
test brightness: 17
