Lens (eye) facts for kids
The crystalline lens is a clear, curved part inside your eye. It works with the cornea (the clear front part of your eye) to bend light. This helps to focus the light onto the retina at the back of your eye. The lens can change its shape. This changes how your eye focuses, allowing you to see objects clearly whether they are far away or close up. This amazing ability of your lens to adjust its focus is called accommodation. It's a bit like how a camera adjusts its lenses to get a clear picture! The lens is flatter on the side facing the front of your eye.
The lens is also known as the aquula or crystalline lens. In humans, the lens does a lot of the eye's focusing work, providing about one-third of the eye's total focusing power.
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How the Lens is Built
The lens is located in the front part of your human eye. In front of the lens is the iris, which is the colored part of your eye. The iris controls how much light enters your eye by changing the size of your pupil.
The lens is held in place by tiny, strong fibers called the suspensory ligament. These fibers connect the lens to a muscle called the ciliary body. This muscle helps the lens change its shape for focusing. Behind the lens is a clear, jelly-like substance called the vitreous body. In front, there's a watery fluid called the aqueous humor. Both of these surround and protect the lens.
The lens has an oval, curved shape, like a small, clear bean. The front surface is a bit flatter than the back surface. In adults, the lens is usually about 10 millimeters (about 0.4 inches) wide and 4 millimeters (about 0.16 inches) thick. It's important to know that the size and shape of the lens can change when you focus. Also, the lens continues to grow throughout a person's life!
Parts of the Lens
The lens has three main parts:
- The lens capsule
- The lens epithelium
- The lens fibers
The lens capsule is the very outer layer, like a clear skin. The lens fibers make up most of the inside of the lens. The lens epithelium is a layer of cells found between the capsule and the fibers, but only on the front side of the lens. What's really cool is that the lens itself doesn't have any nerves, blood vessels, or connective tissue!
The Lens Capsule
The lens capsule is a smooth, clear membrane that completely covers the lens. It's like a stretchy, protective wrapper. This capsule is made of a strong protein called collagen. It's created by the lens epithelium. Because it's very elastic, the capsule allows the lens to become more rounded when the tiny fibers holding it aren't pulling on it. The capsule's thickness varies, being thickest near the middle edges and thinnest at the very back.
The Lens Epithelium
The lens epithelium is a layer of cells located on the front part of the lens, between the capsule and the lens fibers. These cells are super important because they control most of the lens's daily functions, like keeping it healthy and balanced. They help manage how water, nutrients, and other substances move in and out of the lens.
These cells also create new lens fibers! They are constantly making new fibers throughout a person's entire life, from when they are an embryo to an adult. This is how the lens keeps growing.
The Lens Fibers
The lens fibers make up the biggest part of the lens. They are long, thin, and clear cells, packed very tightly together. They are typically about 4 to 7 micrometers wide (that's super tiny!) and can be up to 12 millimeters long.
These fibers stretch from the back to the front of the lens. If you were to cut the lens horizontally, you would see the fibers arranged in concentric layers, just like the layers of an onion! If you cut it along the middle, it looks like a honeycomb. These tightly packed layers are called laminae. The lens fibers are connected to each other by special junctions that allow them to communicate and fit together like puzzle pieces.
The lens is divided into different areas based on how old the lens fibers are. Moving outwards from the very center (which has the oldest fibers), you'll find the embryonic nucleus, the fetal nucleus, the adult nucleus, and then the outer cortex. New lens fibers, which are made by the lens epithelium, are always added to this outer cortex. Once lens fibers are fully grown, they don't have many of the typical cell parts or nuclei that other cells have.
Related pages
Images for kids
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An image that is partially in focus, but mostly out of focus in varying degrees.
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MRI scan of human eye showing lens.
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Inside the front chamber of the eye.
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The crystalline lens, shown hardened and divided.
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A section through the edge of the lens, showing how the epithelium turns into lens fibers.
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The structures of the eye labeled.
See also
In Spanish: Cristalino para niños
