How does the eye lens focus light onto the retina?
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The eye's lens plays a crucial role in focusing light onto the retina, which is at the back of the eye. To understand how it works, it's helpful to know a little about the structure of the eye.
The lens is a transparent, flexible structure located just behind the iris (the colored part of the eye). It is held in place by small ligaments and is able to change its shape to adjust the focal length.
Here's how the lens focuses light onto the retina:
1. Light enters the eye through the cornea, which is the clear, dome-shaped front surface of the eye.
2. The cornea bends, or refracts, the light to a certain degree. However, the refractive power of the cornea alone is not enough to focus the light sharply onto the retina.
3. As the light passes through the pupil (the opening in the center of the iris), its diameter can change to regulate the amount of light entering the eye.
4. After passing through the pupil, the light reaches the lens. The ciliary muscles, located around the lens, adjust the curvature or shape of the lens as needed.
5. When the eye needs to focus on a nearby object, the ciliary muscles contract, allowing the lens to become thicker and more curved. This increase in curvature increases its refractive power, which helps to bring near objects into focus on the retina.
6. Conversely, when the eye needs to focus on a distant object, the ciliary muscles relax, causing the lens to become thinner and less curved. This decrease in curvature reduces its refractive power, allowing distant objects to come into focus on the retina.
Overall, it's the ability of the lens to change shape that enables it to adjust the focal length and focus light onto the retina, making clear vision possible.