Answer to Question #321497 in Human Anatomy and Physiology for Vicky

Question

How does the mammalian eye focus an image? In your description name the important physical structures in image formation, define the focal point and explain what accommodation is and why it's important? (30)

Answer 1

All the different parts of your eyes work together to help you see.

First, light passes through the cornea (the clear front layer of the eye). The cornea is shaped like a dome and bends light to help the eye focus.

Some of this light enters the eye through an opening called the pupil (PYOO-pul). The iris (the colored part of the eye) controls how much light the pupil lets in.

Next, light passes through the lens (a clear inner part of the eye). The lens works together with the cornea to focus light correctly on the retina. The crystalline lens changes shape (due to ciliary muscle) to accommodate near or far targets. The ability of the eye to change the shape of its lens and its focus is known as accommodation. Think of it as one of the most important functions of the vision system: your natural response to trying to examine something nearby.  Thanks to accommodation, the eyes automatically zero in on the text on your smartphone. When accommodation works right, you see fine details up close in clear focus. 

When light hits the retina (a light-sensitive layer of tissue at the back of the eye), special cells called photoreceptors turn the light into electrical signals.

These electrical signals travel from the retina through the optic nerve to the brain. Then the brain turns the signals into the images you see.

So,

• You focus light with your cornea and lens.
• Your curved cornea bends the light into your eye.
• Your lens changes shape to bring things into focus.
• When you look at things that are far away, muscles in your eye relax and your lens looks like a slim disc.
• When you look at things that are close, muscles in your eye contract and make your lens thicker.