A Review of Rods and Cones of the Eye in Relation to Color Blindness

Rods and cones are two different types of photoreceptors and photoreceptors are cells that absorb light and color and send those signals to the retina which in turn send them to the brain which allows us to see colors. Rods work at low light levels which allows us to see low levels of light in situations where it Is dark. Rods also do not allow us to see color which explains the reason behind humans not being able to see color at very dark locations.

Also, rods are not very sensitive which means that it is hard to detect small changes in light in dark spaces. Rods in addition to that only have 1 type of pigment which also explains why we cannot see color with them.

Cones on the other hand do see color and are what we use most of the time to see color. There are 3 different pigments of cones, blue, green, and red and the human eye has around 6 million cones.

Also, humans can see the color white only when all the cones are stimulated which the brain recognizes as “white”. We can see colors other than the pigments’ colors due to some of the different pigments of cones being more stimulated than others. For example, you can see brown because your green and red cones are being stimulated while as your blue cones are not. The shade of the color depends on how much light they are absorbing and the wavelength of light that is passing through them.

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Color blindness is an inherited condition which makes the patient lack some photoreceptors which causes the brain to interpret some colors differently. Color blindness may be caused by some of your cones missing for example, the red cone which would prevent you from seeing red and some other colors because the cones’ colors mix to create other color. E.g. red and green mixes to make brown, so if your red cone was missing you would not be able to see brown in addition to red. There are 3 main classes of colors blindness; monochromacy: the total color blindness which is caused by 2 or 3 of your 3 cones missing. This would make you see only 1 colors depending on which cone is missing or it could make you see no colors and only in monochrome. Dichromacy is the absence of one of your 3 cones which doesn’t allow you to see some colors e.g. red. Anomalous Trichromacy is another type of colors blindness which causes alteration in one of your 3 cones’ pigments. This causes alteration in colors rather than total loss of colors which would be dichromacy. This is by far the most common type of color blindness.