The human eye is one of the most complex systems in a human body. It contains roughly two thirds of the body’s sensory receptor cells. The human eye can distinguish around 10 million different colours, and is not shaped as a perfect sphere, but instead curves more at the front. The human eye is responsible for allowing us to the see the world we live in.

Eye(127183)Credit: morguefile

How We See

How to eyes judge distance?

Because your eyes are spaced apart, each eye will see things from a slightly different angle. It is the brains job to sort out these two different images to establish a clear picture. As these images of what you are viewing travel down the optic nerve and reach the brain, they are actually upside down. The brain turns the image the right way up, allowing you to see things as they should be.

The Difference In Eye Colour

Why are some eyes blue and others brown?

Eye colour is determined by the amount of pigment, known as melanin, they contain. Brown eyes have high levels of melanin, while blue eyes have very little. Our melanin levels are determined by our genetic make-up that we inherit from our parents. When both parents have the same eye colour, usually their child will inherit the same colour. Brown eyes tend to dominate. So when one parent has blue eyes and the other parent has brown eyes, generally the child will be born with brown eyes. However, because of the complex nature of the genetic make-up of our eyes, there are exceptions to this rule.

There is also cases of people who two different coloured eyes, which is known as heterochromia of the eye. There are two types of heterochromia, ‘complete’ means that one iris is a different colour from the other iris, and ‘partial’ means that only part of an iris is a different colour from the rest of the iris.

Glasses and Laser Surgery

There are two main types of vision conditions that are corrected through glasses – near-sightedness and far-sightedness. People who have normal vision have eyes that focus light straight onto the retina at the back of their eye. In cases of near-sightedness, people have eyes that focus light in front of the retina, so they can’t see things that are far away. In cases of far-sightedness, people have eyes that focus light behind the retina, so they can’t see that are close and have to have glasses to be able to read. In both cases, lenses in the prescription glasses are designed to re-focus the light back onto the retina.

Laser treatment has fast become a possible procedure to fix some eye conditions. During the procedure, a laser is directed on to the cornea, where the laser can then reduce the thickness of the cornea, enabling the eyes to correctly focus on to the retina instead of before or beyond it.

Eye Facts

  • If you could add up all the time you spent blinking during your lifetime, you would have spent 1.2 years blinking.
  • Only one sixth of the eyeball can be seen outside the body.
  • Sailors used to believe that a gold earring would improve your eyesight. This is defintely not true. 

If you are interested in finding out more interesting facts about the human body, you can continue learning about muscles or hair.