1) A pupil regulates the incoming light, like the diaphragm of a camera. In brighter places, it closes, avoiding an “overdose” of light. Already in the dark, it dilates. The variation ranges from 2 to 8 mm in diameter – which is equivalent to magnifying the amount of light reaching the eye by up to 30 times.
two) Who contracts or dilates the pupil is the iris, a type of muscle tissue. When we are born, it is usually clear, almost blue. Over time, it receives pigments that can turn the eye green or brown. the deposition of the pigments and iris relief are never the same, making them unique, like our fingerprints.
3) The cornea and the crystalline they work like a set of lenses in a camera, focusing light rays sent to the retina at the back of the eye. Because it is a lens that refracts light, it forms an inverted image.
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4) At retina, there are about 100 million photoreceptors that convert light into electrical impulses. But only one type of them, the cones, detect color. Another type, the rod, helps us see in dim light. The retina uses a vitamin A derivative to absorb light at night. This is why a lack of this nutrient can lead to night blindness.
5) The electrical impulses with the codes of color, luminosity and limits of the shape of the observed object travel through the optic nerve up to the brain. The cortex translates these impulses, perceives the movements and creates an image in our mind.
6) At the connection of the optic nerve with the retina, there is a stain – it is our «blind spot». But we don’t see a black hole, because the brain compensates for the flaw, covering it with the image captured by the other eye.
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better than a camera
The human eye has greater capacity than digital cameras
We can see in almost complete darkness, because our vision is 600 times more sensitive to light than the most modern digital cameras (if we were an analog camera, instead of traditional ISO 100 film, we would have ISO 60,000 film!) a 50mm camera lens has an average field of view of 32 degrees. The human eye would correspond to a 22.3 mm lens, with a field of view of around 150 degrees. However, we only see an area of just 10 degrees in focus.
daily blindness
Brain compensates for vision failure
Every time the eye changes focus (between one object and another, for example), the nervous system stops receiving visual information for about 0.1 second. But we don’t realize it, because the brain fills these moments with artificial images that give us the feeling of continuous movement. Adding these moments, it’s like we spend four hours a day blind!
changing the tone
Tonality with which we see the world changes with age
- Birth: Newborns see very poorly, seeing the blurry world. In addition, they cannot direct their eyes to a fixed place.
- 2 months: We see in colors since we were born, but it’s only around that age that we can distinguish similar tones, such as red and orange.
- Four months: We can identify faces and babies develop depth perception, knowing if something is near or far
- 8 months: Our vision is complete but shaky. The eye continues to grow, which can cause lifelong maladjustments such as astigmatism and myopia.
- 8 years: Neuronal connections are stabilized. Learned visual functions are no longer forgotten. We see the world in a bluer tone
- 23 years: It is the age at which a man’s eye finally stops growing (for women, it is at 25). Therefore, it is at this age that myopia surgery is suggested.
- 40 years: From that time on, the crystalline lens starts to lose its elasticity and it is difficult for us to see up close.
- 60 years: The lens begins to become cloudy and yellow, causing cataracts. As a result, we begin to see the world in more red and yellow tones.
CONSULTANCY Paulo Henrique Ávila Morales, ophthalmologist at the Federal University of São Paulo
SOURCES Books Musical Hallucinations It is An Anthropologist on Mars, by Oliver Sacks; BBC documentary human senses; newspapers BBC News, Daily Californian It is The Guardian; and website TechWorld