How the eye works

The rays of light emitted from an certain object within the eye's viewing range, enters the cornea and is focused onto the lens which focuses the light onto the retina. The pupil can dilate and contract and contract to focus on an object. The Iris reduces the number of rays entering the eye and hence reduces the intensity. The image formed is upside down and the brain coverts the image to be upright. 



The retina contains cones and rods which detect colour and play a role in converting the image to neural signals (so the image can be sent to the brain). These are called photoreceptors. Of course cones and rods are not the one and only things that convert light signals to neural signals, there are seven layers of cells in the retina that convert the image seen. Below is a diagram of the complexity of the process. 


Rods detect light and dark. Cones detect colour, there are three types of cones which all detect different colours. There are cones which detect red, cones which detect  blue and cones which detect green. Anyone who has studied physics will know that these are the primary colours for light (these 3 colours can make any colour so therefore the eye can detect every colour). The the macula lutea is a region in the retina that contains a high concentration of cones but a low concentration of rods. Most light is focused on this region. This causes humans to have high resolution colour images. The fovea contains the highest concentration of cones and barely any or no rods, it is located in the macula lutea region.

The optic nerve where the messages get sent to the brain. No cones or rods are here so this is also referred to as a blind spot. You can locate your blind spot by closing your right eye and concentrating on the dot. Start at about 60cm from your monitor and gradually move closer to the monitor. At a point you should find that the cross will disappear. This is your blind spot.



As you can see, our eye is very complex and the way we see is quite remarkable. I hope you now have a basic understanding of how the eye works in context to colour blindness.

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