23 Sep Understanding How Your Eyes Work
Your eye works in a similar way as a camera. When you look at an object, light reflected from the object enters the eyes through the pupil and is focused through the optical components within the eye.
The front of the eye is made of the cornea, iris, pupil and lens, and they focus the image onto the retina. The retina is the light sensitive membrane that covers the back of the eye. This membrane consists of millions of nerve cells which gather together behind the eye to form a large nerve called the optic nerve.
When the light enters the eye, it is focused to a pinpoint on the macula, a small area in the center of the retina at the back of the eye. The macula is responsible for central detailed vision, allowing you to see fine detail and color, read and recognize faces.
When light stimulates the nerve cells in the retina, messages are sent along the optic nerve to the brain. The optic nerves from the two eyes join inside the brain. The brain uses information from each optic nerve to combine the vision from the two eyes allowing you to see one image.
To see clearly, the cornea and the lens must bend (refract) light rays so they focus on the retina. If the light rays don’t properly focus on the retina, the image you see will be blurry. When this happens, it is called a refractive error.
Refractive errors are caused by an imperfectly shaped eyeball, cornea or lens — or in the case of presbyopia, a lens that can’t change shape enough to focus on close objects — and are of these basic types:
- Myopia is another word for nearsightedness, where only nearby objects are clear.
- Hyperopia is another word for farsightedness, where only objects far away are clear.
- Astigmatism is when images are blurred, regardless of whether they are near or far.
- Presbyopia is a common condition that typically develops between ages 40 and 50 and makes it more difficult to see very close. It can be corrected with bifocals or reading glasses, but usually can’t be corrected by LASIK or some other refractive surgery.
Glasses, contact lenses and refractive surgery such as LASIK try to reduce these errors by making light rays focus on the retina.