Colour vision

Question 1

What is colour vision?

Answer 1

Colour vision is an illusion
Colour vision is created by the interactions of neurons in our eye and visual cortex, it is projected onto the world we see

Question 2

Why did colour vision develop?

Answer 2

Permet d’offrir plus d’information sur les objets
- Form perception colour : distinguish surfaces on basis of energy and wave length
- Food
- Mating
- Pollination

Question 3

Fraction visible d’une champ électromagnétique perçu par les yeux?

Answer 3

Eye sensitive to small fraction of the energy : spectrum between 400-700 nm

Ondes plus longues : radio waves, microwaves
Ondes plus courtes : x-rays, gamma-rays

Question 4

Quelle molécule contient les opsins?

Answer 4

Retinal
Light sensitive opsins contain a molecule « retinal » which changes shape when it absorbs a photon of light

Question 5

Quels sont les 4 types de photorécepteurs dans la human retina?

Answer 5

S-cone : short wavelength (blue) = 420 nm
M-cone : medium wavelength (green) = 534 nm
L-cone : long wavelength (rouge) = 564 nm
Rods = 498 nm

Question 6

Rods versus cones peak of densities

Answer 6

Rod peak : 18° de la fovea
Cone peak : fovea

Question 7

Combien de récepteurs différents faut-il minimalement pour avoir une colour vision?

Answer 7

Colour vision requires at least 2 different types of light receptor which response optically to different wavelengths of light

Question 8

Que signifie tricromacy?

Answer 8

Trichromacy : depends on 3 classes of retinal cone photoreceptors
Each type of cone covers a range of frequencies.
Primarily sensitive to a particular portion of the spectrum.
S-cones : bluish-violet light
M-cones : bluish-green
L-cones : yellowish-green

Question 9

Quels sont les types de cones les plus fréquents sur la rétine?

Answer 9

Majority of cones in the retina are L-cones and M-cones.
The ratio of L to M cones varies across individuals
L and M cones have a random spatial arrangement across the retina
Foveal pit contains mainly L & M cones

Question 10

% de photorécepteurs s-cones sur la rétine?

Answer 10

S-cones account for 8-10% of all retinal photoreceptors
S-cones have a very low density in the foveal region (3-5% of total cone population)
Maximum density of 12-15% on the foveal slope (1 degree from foveal pit)
8% of the total cone population elsewhere in the retina
Most sensitive to blue-violet light

Question 11

Vrai ou Faux concernant les cones :
1. Ratio of S to L & M cones is CONSTANT
2. Ratio of L to M VARIES

Answer 11

Réponse : VRAI pour les deux énoncés

Question 12

Vrai ou Faux : Chromatic contrast requires large areas

Answer 12

Vrai

Question 13

What are the two types of colour opponent ganglion cells?

Answer 13

Several PR may send their information to one ganglion cell.
Certains colours are NEVER seen in combination.
Cannot see reddish green or bluish yellow.
There are two types of colour ganglion cells :
- Red/Green
- Yellow/Blue

Question 14

Quels cones inhibent versus activent les Blue/Yellow ganglion cell?

Answer 14

The Blue/Yellow ganglion cell is EXCITED by BLUE cone stimulation and INHIBITED by the sum M and L cone activation.

Question 15

Quels cones inhibent versus activent les Red/Green ganglion cell?

Answer 15

Red light stimulates red cone, which INCREASES firing in Red/Green ganglion cell

Green light stimulates the green cone, which decreases firing the Red/Green ganglion cell

Question 16

Types de congenital deficits des couleurs

Answer 16

Protanopia (longer wavelength : red/green confusion)
Deutanopia (middle wavelength : red/green confusion)
Tritanopia (short wavelength : blue/yellow confusion)
Rod monochromacy
S-cone monochromacy

Red-green le plus fréquent : 7-10% chez les H, X-linked

Question 17

What is Köllner’s rule for acquired colour deficits?

Answer 17

Patients with RETINAL disease develop BLUE-YELLOW discrimination loss, whereas OPTIC NERVE disease causes RED-GREEN discrimination loss
- BLUE-YELLOW : Rétine
- RED-GREEN : ON

Exceptions include glaucoma (initially blue-yellow), central cone degeneration (may be red-green)

Question 18

Zones du cortex impliquées dans les couleurs?

Answer 18

Colour and form : V1 + V2
Mainly colour : V4

Cerebral achromatopsia is due to damage to brain areas responsible for colour processing (V4, temporal lobe)

V2 et V4 are highly metabolically active; more than other areas of the cerebral cortex. Therefore they are prone to effects of reduced oxygen delivery which might result from stroke

In rod monochromatism, there is an absence of cones. Vision is monochromatic and visual acuity is poor. In contrast, in cerebral achromatopsia the retina is not damaged and the patient may have excellent acuity.

Question 19

Quels déficits en couleur permet de détecter l’Ishihara?

Answer 19

N colour vision can read numbers : 25, 6, 8, 56, 29, 45
Protanopes and deuteranopes peuvent seulement lire : 25 et 26
A

Question 20

Quels déficits en couleur permet de détecter l’Ishihara?

Answer 20

N colour vision can read numbers : 25, 6, 8, 56, 29, 45
Protanopes and deuteranopes peuvent seulement lire : 25 et 26
Tritanopia can read all numbers … permet pas pas de Dx

DONC Ishihara pour common RED-GREEN colour vision defects

Versus HRR permet de tester pour les 3 axes de couleurs : protan, deutan et tritan