How the Eye Works

There are few parts of the human body more amazing than our eyes. We often take them for granted, but these tiny cameras spend every day processing millions of pieces of information at lightning-fast speeds – and turns them into the simple images we see almost instantly.

In reality, this process is anything but simple. The eye has several distinct parts, each of which has specific responsibilities that work together like a machine.

How exactly does this process work, and what are the major parts of the eyeball involved in creating vision? Let’s find out.

 

Like a Camera

The eyeball is just like a camera. In fact, within the scientific community, human eyes are part of a classification known as “camera-type eyes.” And just like a camera, it can’t function without the presence of light.

As light hits the eyes, it’s focused by the eye in a way similar to a camera lens. This process allows the images we see to appear clear and sharp rather than blurry.

Early Process

There are specific parts of the eye that make this focusing process possible. Each beam of light that hits the eye goes through a series of steps:

• 1. Light passes through a thin layer of moisture
• 2. Light hits the cornea, also referred to as the eye’s “front window.” The cornea is transparent, and is the first layer to begin focusing light within the eye. The cornea is connected to the sclera, which is a tough fiber on the outside of the eye that acts as protection.
• 3. Behind the cornea is another liquid layer known as the aqueous humor. Its job is to maintain pressure levels in the front of the eye as light is passing through.
• 4. Once light has passed through the aqueous humor, it has finally reached the pupil. The pupil is the entryway to the iris, and most people are familiar with the pupil because of the way it changes its size when differing amounts of light are cast into the eye.
• 5. Once the pupil determines how much light it will let inside your eye, the job passes to the lens. The lens factors in the amount of light the pupil lets in, and figures out how far away you are from the object that the light is reflecting off of, or the object you’re trying to see. From there, the lens shapes your image into an accurate view of what you’re looking at. Part of this process is controlled by muscles in the lens called ciliary muscles, which expand and contract to pull on the lens and allow it to gauge distance properly.

Finishing the Picture

When light reaches the center of the eye, it’s ready to be processed. It first passes through another layer of moisture, called the vitreous, or vitreous humor. After that, it reaches the final stop in the process: The retina.

The retina is the back of the eye. If the lens in your eye is most like a camera, the retina is most like its film – this is where the final product is projected. The retina has several parts:

• Macula: The center of the retina. The center point of the macula is called the fovea, and it has the most nerve endings of any part of the eye.
• Photoreceptors: Split into two designations – rods and cones. Rods are used for limited light and color, and cones are used for specific color detail. The rods and cones take light and convert it into electronic signals for the brain to process.
• Retinal pigment epithelium: Abbreviated RPE, this is a tissue layer below the rods and cones which absorbs any extra, unneeded light.
• Choroid: The choroid is behind the retina, and is in charge of making sure the retina and RPE have enough nutrition blowing from small blood vessels.

Once the photoreceptors have converted light into an electronic signal, they send a signal to the brain’s visual command center and you have vision. It’s amazing what even small parts of our bodies can do. 

 

Revere Health Ophthalmology offers patients the best in eye care, from glasses and contacts to treatment of eye-related diseases and conditions.

 

Sources:

“Vision Basics: How Does Your Eye Work?” WebMD. http://www.webmd.com/eye-health/amazing-human-eye
“How the Human Eye Works.” LiveScience. http://www.livescience.com/3919-human-eye-works.html