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how does the spectral sensitivity graph of a protanope looks like?
- the s and m cones overlap from 400nm to 545nm.
- they have monochromacy above 545nm
- this is their distinguishable spectrum
- neutral point =492
how does the spectral sensitivity graph of a deuteranope look like?
- similar to that of protanope overlap
- they won't be able to distinguish anything above 545 either (monochromacy)
- their neutral pt is 498nm though
how does the spectral sensitivity graph of a tritanope look like?
- they don't have monochromacy!! (lucky them)
- neutral pt=569nm
what is the genetics of tritanopes like?
- lack cyanolabe
- autosomal DOMINANT
- very few in both genders
- they can't distinguish blue from yellow but they can tell the difference in color using their red and green pigment
- confusion line = 569nm (aka neutral pt)
- yellow looks more pink and blue looks more green
what is the wavelength discrimination like for tritanopes?
they have poorer wavelength discrimination
what is tritanope's spectral sensitivity like?
- not as sensitive to lower wavelength of light cuz they don't have blue curve
- their luminous efficiency curve peaks at 555nm
- blue wavelength of light will look dimmer and they will need more intensity to detect them
how are we physiologically organized at the fovea?
- center of fovea only has L and M cones
what is trichromacy?
- got 3 cones
- can match any spectral color with some combo of three suitable primaries
- types: normal and anomalous
what are some types of anomalous trichomats?
- deuteranomlous trichromacy
what is anomalous trichromacy?
- protans and deutans are inTRAgenetic crossover defect
- result in abnormla gene (hybrid) for erythrolabe/chlorolabe
- they have shifted spectral sensitivity curve
- color matching, spectral sensitivity and wavelength discrimination characteristics as though they have less than normla amount of the affected pigment
- no confusion line - disorted macadams ellipse on CIE
- no co-punctal points
- no neutral points
what is deuteranomaly?
- abnormal gene for chlorolabe - spectral sensitivity shifted slighted towards red
- x-link RECESSIVE
- 5% male
- 498nm least saturated
what is protanomaly?
- abnormal gene for erytholabe
- Spectral sensitivity shifted slightly towards lower (greener) wavelengths.
- Or, erythrolabe is missing and there is a second M-cone (which is shifted towards longer wavelengths). They have two M cone genes, one of which is a hybrid that acts like an L cone photopigment
- x-link RECESSIVE
- 492 least saturated
what is tritanomaly?
- abnormal gene for cyanolabe
- autosomal DOMINANT
- max photopic sensitivity at 555nm
- 570 nm appears least saturated
- normal trichromats will see yellow, tritans will see white
what is the spectral saturation of anomalous trichromats like?
- able to distinguish color across the whole spectrum, but they need more saturation than normal trichromats
- can distinguish the wavelenghts dichromats can't (498, 498 and 569) but they need a lot of saturation to do it.
- the curve is shifted to the left and down
anomlous trichromats wavelength discrimination
- x-axis = wavelength
- y-axis =just noticeable difference
- anamalous trichromats still have the double hump line on the graph as the normal trichromats so their discrimination is similar to a normal trichromat but is reduced
what is color asthenopia?
- uncomfortable color vision
- Exhibited by some anomalous trichromats and even some normal trichromats
- Ability to discriminate among different wavelengths worsens with prolonged viewing until they behave as dichromat of the same "type" (i.e.,protan, deutan, or tritan).
what is color amblyopia?
- Poor color discrimination that is not associated with any documentable pathology or genetic defect
- May be transient or permanent
- Very rare. You have to rule out everything else before you diagnose them with this
what are some acquired color defects?
- We assume blue-yellow defect is acquired. They are very rare so it makes more sense clinically to assume that are acquired
- the disease progresses, so does the defect
what is Kollner's Rule?
- Acquired blue-yellow defects are from ocular media,
- choroid, & distal (outer) layers of the retina.
- Acquired red-green defects are from the optic nerve and more proximal (inner) parts of the visual pathway
how do you get acquired color defects?
- Optic nervedamage
- Occupational exposure (chemicals)
- Toxicity to medications
- - Antibiotics
- - Chloroquinines
what is chromatopsia?
- A distortion of color vision such that the entire visual world appears tinted, as though viewed through a lightly colored filter
- xanothopsia and cyanopsia
what is xanthopsia?
- Yellowish tint to visual world
- Temporary side-effect of fluorescein angiography
- Also associated with digitalis poisoning
what is cyanopsia
- bluish tink to visual world
- frequently desribed by patients immediately after nuclear sclerotic cataract extraction
what are some things you might see with acquired color vision anomalies?
- Nearly always associated with disease or injury
- May be monocular or more severe in one eye than the
- May vary in severity over time
- May not exhibit typical deutan, protan, or tritan characteristics or test findings
- More likely to present with errors in color naming
- Equally prevalent among males and females
Kollner's Rule of Thumb
- Blue-Yellow (tritan)
- - ocular media (nuclear sclerotic caratact)
- - outer r & choroid (ARMD)
- - diabetic retinopathy (this is inner retina so it's an exception)
- Red-Green (protan or deutan)
- - inner retina (toxic amblyopia; papillitis; Stargardt's)
- - optic nerve and neural pathways (optic neuritis MS)
what are some exceptions to Kollner's Rule of thumb?
Glaucoma, papilledema, and dominantly inherited optic atrophy (all are optic nerve disorders) may be associated with B/Y (tritan) color vision deficits rather than the predicted R/G deficits
hm... Kollner’s Rule is a “Rule of Thumb” (which rhymes with dumb)
- Many if not most (if not ALL) acquired red-green defects also exhibit blue-yellow defects
- Exceptions to Kollner’s Rule include glaucoma,
- papilledema, & all optic nerve disorders, which maybe associated with a blue/yellow defect
- Acquired defects may be UNILATERAL
- Congenital are always bilateral
what is blackbody radiator?
a (theoretical) perfect radiator of electromagnetic energy, the spectral characteristics of which are defined entirely by the blackbody’s temperature
what is color temperature?
- The color temperature of a light source is that temperature (in degrees Kelvin) of a blackbody radiator that produces the same spectral output as that of the real light source.
- “Color temperature” should be used to describe only incandescent light sources
what is correlated color temperature?
The correlated color temperature is the temperature of a blackbody radiator that produces an output that most closely matches the color of the light emitted from a real non-incandescent source
what are some CIE "standard illuminants"?
- illuminant A
- illuminant B
- illuminant C
- D (daylight) illuminants (D55, 65, 75)
- We need a standardized light source when doing color testing so we have consistent results. We want a light source that emits all wavelengths of light as equally as possible so it won’t affect the testing
what is spectural locus on CIE?
the curved part of the CIE that has all the spectral wavelengths
what is purple locus of CIE?
the straight part at the bottom
what are non-spectral purples?
these colors are not made up by a single wavelength.You have to mix more than one wavelength to get these colors
what is Planckian Locus of CIE?
- the line of various standard illuminants
- all of these are considered white light
- blackbody radiator "color temperature"
explain illuminant A
- Definition: Blackbody radiator at 2856° K
- CIE Source: Gas-filled coiled-tungsten filament lamp with a fused-quartz envelope or window operating at 2854° K
- Function: Serves as standard for illuminants B & C
explain illuminant B
- color temp: 4874° K
- CIE Source: Illuminant A + 1 cm thick double cell optical glass container (Davis-Gibson filter) filled with liquid chemical solutions B1 and B2
- Function: Mimics direct sunlight at noon (poorly)
explain illuminant C
- Color Temperature: 6774° K
- CIE Source: Illuminant A + 1 cm thick double cell optical glass container (Davis-Gibson filter) filled with liquid chemical solutions C1 and C2
- Function: Mimics average direct Northern sunlight but lacks power in near UV range important for fluorescent materials
- Illuminant C is the illuminant for which nearly all clinical color vision tests were designed (approx best by MacBeth lamp)
explain illuminant D
- Represent measured spectra under different conditions of natural daylight
- Correct for weaknesses of the other standard illuminants (A, B, & C) in near UV
- The D illuminants have no standard sources ( Instead, there are standard tests to be passed)Illuminant D65 is an acceptable substitute for Illuminant C for color vision testing
explain illuminant D65
- Recommended for “Natural” Daylight
- Correlated Color Temperatures: 6500° K
- Fluorescent sources
- CIE Standard Source: NONE → functional tests are provided
- Acceptable substitute for Illuminant C in clinical color vision testin
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