Eye

The eye is an organ used for vision, which means seeing the world around us. Humans usually have two eyes placed on the front of the head. The main job of the eye is to detect light and send information to the brain. The brain then turns this information into images. Many animals also have eyes, though their shape and ability can be different. Some eyes can see colors, while others can only see light and dark.

Light enters the eye through the cornea, which is a clear outer layer. Behind it is the pupil, a dark round opening in the center of the eye. The pupil controls how much light enters. In bright light, the pupil becomes smaller. In dim light, it becomes larger. Around the pupil is the iris, which is the colored part of the eye. The iris moves to change the size of the pupil.

After passing through the pupil, light goes through the lens. The lens is clear and flexible. It changes shape to focus light. This process is called focusing. Focused light then reaches the retina, a thin layer at the back of the eye. The retina contains special cells that react to light. These cells are called rods and cones. Rods help with seeing in low light. Cones help with seeing colors and details.

The retina changes light into electrical signals. These signals travel through the optic nerve to the brain. The optic nerve is like a cable made of many nerve fibers. The brain receives the signals and creates an image. This image appears upright, even though the light entering the eye is upside down. The brain corrects the image without us noticing.

Eyes need protection because they are sensitive. Eyelids, eyelashes, and tears help protect them. Eyelids close to block dust or strong light. Eyelashes stop small particles from entering. Tears keep the eye moist and wash away dirt. Blinking spreads tears across the surface of the eye. This helps keep vision clear.

Different animals have eyes that work in different ways. Birds of prey can see very far. Cats can see well in the dark. Insects have compound eyes made of many small parts. These eyes are good at detecting movement. Even though eyes vary widely, their basic purpose is the same: to receive light and help the brain understand the surroundings.