Eyes specialize in focusing light from the surroundings, and sending a signal to the brain. Human eyes are especially complex and the way they collect and focus light uses similar principles as a microscope.

Our eyes are designed to see things in air, which means that they don’t see that well in water. Other mammals such as seals have eyes that work better in water than in air.

Many factors affect eyesight, and scientists don't know for sure exactly how they all work. Here are some current theories about things that affect your eyesight.

Scientists think that repeated eyestrain can damage your vision. So if you can't quite read something, it's better to move closer before you try again, instead of squinting and trying harder. Also make sure to work under normal light, instead of straining your eyes in the dark or in very bright light.

Scientists think that normal exposure to daylight can protect your vision. This includes being exposed to sunlight during the day, and being in the dark at night. So it's better to use your eyes during the daytime and sleep at night, instead of using electrical lights when it's dark outside.

Finally, part of your eyesight just comes from your parents. A lot of people can't help becoming nearsighted as they grow up. Luckily, technology can still help nearsighted people see clearly. Common uses of technology are glasses, contact lenses and vision correction surgery (or laser eye surgery).