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Which of the following spectrum of colour is highest visualized due to central cones?

A Red Blue
B Blue Red

C Blue Green
D Red Green

Ans. D Red Green

a. Colour vision:-

i. The appreciation of colours is a function of the cones and occurs only in photopic vision.

ii. Young — Helmholtz theory of the colour vision: -

b. Three types of cones: -

i. Short wave pigment or Blue sensitive or cyanolabe à absorbs Light maximally in blue- violet portion spectrum.

ii. Middle wave or green sensitive or chlorolabe — absorbs maximally in green portion

iii. Long wave pigment or red sensitive or Erythrolable à absorbs maximally in the yellow portion

c. “Blue, green and red are the primary colours but the cones with their maximal sensitivity in the yellow portion of sensitive enough in red portion to respond to red light at a lower threshold than green”.

d. Ref. Samson à Written that à

i. “The peak sensitivity of scotopic vision (twilight vision, function of rods) is approximately 500 nmQ, whereas that of photopic vision (daylight, function of cones) lies at about 560 nm Q ” This differenece accounts for the so called Purkinije-shift Q— a difference in the luminosity of colours in light of different intensity.

ii. Wavelength spectrum of colour à

Basic Tastes Areas Of Tongue

Sweet At the tip of the tongue Q

Sour Along the edges of the tongue Q

Bitter On the back of the tongue Q

Salt On the anterior dorsum of the tongue Q

e. Red + green = yellow: Blue + yellow. = white

f. The colors best appreciated by central cones of foveo-macular area are Red and green Q

g. Conclusion

Since peak sensitivity of photopic vision (cones) lies at about 560 um (yellow — colour) Q and yellow= Red + green, Q Hence answer is Red — green

h. Colour blindness: -

a. Red — green blindness is more common in congenital type.

b. Protonope à red sensation missing Q

i. Deuteranope à green sensation missing Q

ii. Tritanope à blue sensation missing Q

c. Test for colour blindness

i. Isihara’s test à for routine testing particularly for —green blindness. Q

ii. Farnsworth Munsell 100 hue test àScientifically most accurate

iii. Edridge - Green - Lantern test àmainly important for engine drivers

iv. Holmgren’ s wools test

v. Negel’s anomaloscope

Vision Flashcard List

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