Lecture 5 and 6 (starting pres 4-end) Flashcards
Which pathway is isolated using a high TEMPORAL frequency? What function does this allow us to obtain?
MAGNOcellular (aka luminance) pathway
-relative luminous efficiency function…plots shifts in the spectrum (normally 555nm) in those w/ CVDs
about where does a protanope’s peak wavelength lie on the relative luminous efficiency plot?
- the deuteranope’s?
- the tritanope’s?
protanope: 535nm (no L cones - shifts toward shorter wavelength) - 535 seen brighter, L wavelengths seen darker)
deuteranope: 560nm
tritanope: 555nm (same as normals)
for protanopes, how do long wavelengths appear compared to short and medium wavelengths?
-what about for protanomalies?
DARKER
protanomalies - result of intermediate curve b/w nml and dichromatic curve
a slow, flickering stimulus isolates which pathway? measures what?
PARVOcellular pathway. Measures detection thresholds
Topic: wavelength discrimination
-Which two wavelengths show OPTIMAL wavelength discrimination in a normal trichromat? i.e. where’s the MINIMA of the wavelength discrim. fxn?)
- Where is the optimum for pro/deutanopes?
- Wavelengths longer than ___nm can’t be discriminated in pro/deutanopes
trichromat: 500nm, 600nm (MOST sensitive to small changes in wavelengths at these wavelengths)
pro/deutanope: 495 (close)
-can’t discriminate above 540nm (where green starts)
**wavelength discrimination SEVERELY IMPAIRED in protanopes and deuteranopes
Tritanopes can’t discriminate b/w which two wavelengths?
between ~450-480nm (where blue is)
T/F: the major axes of trichromats do NOT converge to a single point, as they have a wide range of orientations
true (referencing macadam ellipses w/ different axes in color matching)
T/F: the major axes of ANY dichromat do NOT converge to a single point
FALSE - they DO converge to a single point - aka co-punctal points. They DON’T converge for a nml trichromat, giving them their excellent color discrimination
T/F: Misreads on Ishihara count as errors
-why (esp w/ Ishihara) might this happen?
FALSE- must be excluded in determining whether a CVD is present (i.e. 3/8, 5/6)
-SERIF font
how many errors on the first 16 plates of the 38-plate ishihara is considered a defect?
how about on the first 12 plates of the 24-plate edition?
38-plate: 3 errors = defect
24-plate: 2 errors = defect
Ishihara: excellent ___ and ___. Are these properties still good w/ HRR plates? When would you use HRR plates instead?
Ishihara: high sensitivity, and specificity (won’t miss anyone)
HRR - will miss 10% of CVDs…used for B/Y defect suspicion, OR for QUANTIFYING the type of defect
topic: detection threshold.
- saturation of ZERO produces what color? can two colors been seen as different?
equal energy WHITE - can’t discern until you start to increase saturation
An observer is shown a spot, then the chromaticity is changed around that spot and the observer says the second spot looks like the first. Where must this second spot be relative to the first?
-observers have a good ability to see changes in the __/__ region of the color space, but a poor ability in the ___ region (recall: variability)
within the same MACADAM ellipse.
-each ellipse has a major AXIS, and each axis has a WIDE range of orientations (around 180 degrees)
- GOOD: blue/purple
- POOR: green
Which type of dichromat has a co-punctal point OUTSIDE the color space
-All these lines converging to a single point are termed what?
deuteranope (point has a negative value)
-color CONFUSION lines (observers CAN’T tell the difference between the colors along that line)
which point divides the spectrum into two regions for dichromats?
the neutral point. Pro/deutanopes’ neutral point separates B/Y (since that’s all they can tell the difference between), and tritanopes neutral point separates (R/G)
Co-punctal point locations for:
protanopes?
deutanopes?
tritanopes?
(X,Y)
protanope: 0.75, 0.25 (reddish purple)
deutanope: 1.4, -0.4 (bluish purple)
tritanope: 0.17, 0 (violet)
how are vanishing plates designed?
background and number spots all fall on the same color confusion line; can’t be discerned as separate if CVD present. Amt of saturation = severity of defect (recall: MORE saturation=FARTHER from the color confusion line)
T/F: the spectral anomaloscope is the ONLY test that can diagnose a CVD fully.
True - PIC plates ID can’t identify, classify, and grade all types of CVD separately - anomaloscope does it all
How many plates technically needed for Ishihara for official “diagnosis” (even though it doesn’t diagnose)
16
What is a tetartan defect?
Defect of the vis PATHWAY itself - all three cones nml…post-receptoral connexns abnml
What is HRR GOOD at?
grading the severity
-considered COMPLIMENTARY to ishihara -suggested to do ishi to schreen, then HRR to classify/grade
T/F: the examiner w/ screening plates waits as long as it takes the pt to reply w/ an answer
false - 4 secs and move on. we ain’t got all day buddy..
…but seriously-hesitation IS CONSIDERED and error, may indicate slight CVD
What’s unique about the C’s seen in the cambridge color test?
three different chromaticities fall on the protan/deutan/tritan color confusion lines
- pt must identify where GAP is
- uses a COMPUTER screen - expensive. research purposes only.
hue discrimination tests (farnsworth D15, 100 Hue, LD15) are for more (mild/mod/severe) CVDs
severe
will someone with a slight CVD pass the Farnsworth D15?
probably. Forms TWO groups of test subjects: nml-slight CVD (pass) and mod-severe CVD (fail)
- used for vocational testing
The desaturated Farnsworth (LD15) detects the ____ of the CVDs (picks up on more subtle ones). Useful in (congenital/acquired) CVDs?
severity
acquired!
-color quality control workers - must be precise
Farnsworth 100 Hue will only identify pts w/ ___ and ___ CVDs.
- Do these caps fall on color confusion lines as seen with the D15?
- Where would a CVD subject make mistakes w/ the 100 Hue test?
moderate-severe only
- NO (color confusion lines’ colors would be in different boxes)
- errors where caps are ADJACENT to confusion lines, where confusion lines are TANGENT to the color circle
Munsell 100 Hue: typical axes of confusion for:
- protan
- deutan
- tritan
-grading system? (assume no errors exist around specific axes)
protan: 17, 64
deutan: 15, 58
tritan: 5, 45
superior: 100
How does the city university test relate to the D15?
- does it detect mild CVDs?
- Do protans or deutans make more errors?
- Can this test grade protans?
uses 4 caps: protan/deutan/tritan color conf lines, and the 4th cap is the next cap color from the D15
- nope: only MODERATE-SEVERE (like d15 etc)
- DEUTANS = more errors (>5 errors =severe deuteranomalous)
- NO - can’t grade protans
Anomaloscope - GOLD STANDARD for testing CVDs. Two types: R/G and B/Y: names? Which one can be used for tritan defects?
- In the upper half, ____ is FIXED (try to match it on the bottom)
- in the bottom half, ____ is fixed
Nagal, Neitz, Oculus –> Oculus can be used for tritans
- upper: luminance
- bottom: hue
hue mixture field (upper half): 0-73 (546nm-670nm) -which two colors are at these wavelengths?
-how does this relate to the fact that a trichromat imitates a dichromat because of this?
546-pure green
670-pure red
S-cones are NOT sensitive to anything in this range - it’s as though they don’t exist! Only using M and L cones to detect deutan or protan defects!
anomaloscope: trichromats act as dichromats (d/t isolation of S-cones), and dichromats act as ___chromats - they only have to change what parameter to get the colors to match?
monochromats - change LUMINANCE only!!
so a TRICHROMAT using the anomaloscope must use an appropriate combination of HOW many wavelengths? How about a dichromat?
trichromat: combo TWO wavelengths
dichromat: only ONE wavelength, and they can match it by changing ONLY the luminance value (on the bottom)
The anomaloscope uses what fxn to classify whether a pt is a protanope or deutanope?
relative luminous efficiency
- if pt is a PROtanope, they’ll DIM the luminance of the middle wavelength (dim the YELLOW) (b/c they see the longer wavelength as DIMMER and want to match it w/ the middle wavelength)
- deutanopes will set the luminance value close to NORMAL (since their color vision is pretty close to nm) - nml luminance value ~17
What does the Moreland equation measure?
B/Y defects. Don’t need to memorize the formula
Can lanterns be used to identify CVDs?
NO- only to tell whether the observer can tell the two colors apart (maritime, military, avation)
Among the following options, who is most likely to FAIL the lantern test: protanomalous, deuteranomalous, or dichromats?
DICHROMATS (need 3 opsins to discern the difference) -
-anomalies may pass the test - unfortunately, only 75% sensitivity means that 25% of pts will PASS the Farnsworth lantern
Three causes of ACQUIRED CVD?
1) systemic pathology
2) intracranial injury
3) therapeutic drugs
-interesting = acquired might be MONOcular or BINOcular, and also might be SECTIONAL depending on where they affect the retina
acquired CVDs usually present w/ reduced visual ___ and visual ____
- more likely to be what type of defect?
- preference b/w males and females?
reduced visual acuity and visual field
- usually TRITAN defect
- equal prevalence males/females
According to Kollner’s rule, are B/Y or R/G more likely to change first? Based on the principle that what part of the eye is affected first?
B/Y FIRST (inner retina)
R/G LATER (optic nerve)
-Note: important: R/G actually noticed MORE
all of the following can produce an acquired CVD:
DM, Gl, AMD, MS, CSR (central serous), alcoholism (competitive inhibition in liver for conversion to 11-cis retinal), leukemia, sickle cell, dominant optic atrophy
Name 4 drugs that can cause a CVD:
-which test becomes IMPORTANT when you have a pt taking these drugs?
- Digoxin, Ethambutol (both deutan)
- Chloroquine/thioridazine (blue)
- Viagra, Vitamin A deficiency (blue)
FM-100 Hue test (score would keep increasing above 100 if defect is present)
Define:
- color agnosia:
- color anomia:
- cerebral achromatopsia:
agnosia: can’t assc color w/ object
anomia: can’t NAME color (can see them no prob)
achromatopsia: V4 lesion
What’s the main factor in color vision alteration produced by aging changes?
increased LENS density (absorption of short wavelengths)
Name a few occupations with ESSENTIAL trichromatic CV:
military, aviation, electricians, cops, navigation (fishermen, pilots), color matchers (textile workers)
