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The Role of Rods and Cones in the Eye

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The role of rods and cones

Rods and cones are known as photoreceptors. They are specialized cells located in the retina in the back of the eye. They receive and process signals of light and colour which gives us our vision.

Rods are located throughout the eyes retina except in the centre which is called the fovea. They are responsible for night vision and specialize in picking up light signals and determine light and shadows they don't respond to different colours so only see in black and white and shades of grey. They don't register objects as clearly as cones .We have around 120 million rods (which are around 1000 times more sensitive than individual cones). Rods pick up signals from all directions thus improving our motion sensing, depth reception and peripheral vision.

Cones- there are between six and seven million cones in the retina. They are located mainly in the centre of the retina around the fovea. Cones are responsible for colour perception and daylight vision. They enable us to see things clearly sharply and in colour (they don't work well n low lght conditons). There are two types of cones red cones these account for around 64% of the total amount of cones. Green 32% and blue 2%. Cones are best at detecting fine details but can only work in bright light. The eyes constantly move as it causes light to fall on different spots on the retina to keep the colour perception steady.

Night and Stereoscopic vision

Stereoscopic vision is vision in stereo with both eyes. Each eye has strong peripheral vision due to the wide distribution of rods. This enables us to see in more than one directon at a time. It improves our depth perception and awareness of our surroundings.

Night vision is also known as scotopic vision. When we enter a dark place it takes a few minutes to become effective. The sensitivity of rods makes night vision possible. Rods do not perceive the colour red this is why most vehicles have red dash board lights so we can see the darkness outside as well as the lights inside.

Photoreceptors convert light into electrochemical impulses that are transmitted to the brain via nerves. Millions of impulses travel along the nerve fibres of the optic nerve at the back of the eye, to the visual cortex of the brain located at the back of the head. The electrochemical impulses are unscrambled and interpreted here. The image is re-invented so we can see the objet the correct way up.

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