How Do the Eyes Work?
To understand how the eyes work, it's helpful to compare the eyes to a camera. Cameras use a lens and film to produce an image, and in a way, so do the eyes.
Light comes in through the cornea, a clear tissue that covers the front of your eye. The pupil is the dark spot in the middle of your eye. It works like a camera shutter, controlling the amount of light that enters our eyes. When it's dark, the pupil dilates, or widens. When it's bright, the pupil gets smaller. Surrounding the pupil is the iris. This is the colored ring of muscle fibers that help the pupil change size.
When you look at an object, light rays enter your eyes. These light rays are bent and focused by the cornea, lens, and vitreous. The vitreous is a clear jelly-like fluid that fills the inside of your eye. The lens' job is to make sure the rays come to a sharp focus on the retina at the back of the eye. Think of the retina as the film in the camera. It's lined with light-sensitive cells, called photoreceptors, that capture, upside-down, the images in our visual field. The sensitive macula, critical for sharp focus, is the most active part of the retina. A healthy macula helps us read small print and see the images in our direct line of vision. When light rays reach the retina, they're converted into electrical pulses that travel through the optic nerve to your brain. It is there that the image gets flipped right-side up.
Vision Screening Guidelines
Guidelines for Adults
- At least one test between ages 20 and 29 and at least two between ages 30 and 39
- Vision tests every two to four years between ages 40 and 65 and every one to two years after age 65.
Guidelines for Children
- Children five years and younger should have their eyes checked each time they see their pediatrician. Teens should be examined once a year.
If you are experiencing any vision problems, it's a good idea to get checked more often.
Protecting the Eyes & Vision
While we can't control the risk factors that make us more vulnerable to vision problems, it's important to exercise caution:
- Know your family's medical history;
- Protect your eyes with sunglasses that absorb 100 percent of damaging ultra violet rays;
- Stay away from cigarettes which contain chemicals that can damage the eyes; and
- Eat a healthful diet.
Types of Vision Problems
It's normal for our vision to deteriorate as we age. Here are some very common vision problems that can usually be corrected with glasses or contacts:
- Farsightedness. This occurs when you can see well at a distance, but not close up.
- Nearsightedness. This is also called myopia. It occurs when you can see well close up, but not at a distance.
There are some vision problems that are much more serious and can even lead to blindness.
If you have a family history of eye disease, you'll have a higher risk of developing vision problems. You may also have other risk factors like previous eye injury, premature birth, diseases that affect the whole body, like diabetes, high blood pressure, heart disease, or AIDS. The only way for you to know for sure if you have serious eye problem is by having an eye exam given by an Optometrist (O.D.) or an Ophthalmologist (M.D.).
- Glaucoma. This occurs when the pressure of the fluid inside your eyes damages the fibers in your optic nerve, and causes vision loss. If left untreated, you can lose your eyesight altogether.
- Cataracts. A cataract means a 'clouding' of all or part of the normally clear lens within your eye, which results in blurred or distorted vision.
- Conjunctivis. This is commonly known as Pink Eye. It is caused by an inflammation of the conjunctiva. This is the thin, transparent layer that lines the inner eyelid and covers the white part of the eye. The inflammation is usually caused by a virus, and will resolve without any treatment. But, sometimes pink eye is caused by a bacterial infection and will require antibiotics.
- Eye Floaters. These may look like small dots or lines moving through your field of vision. They're actually tiny clumps of gel or cells inside the vitreous fluid in the eye. They may be a sign of retinal detachment and you should call your doctor right away.
- Macular Degeneration. This results from changes to the macula portion of the retina. The macula is responsible for clear, sharp vision. This condition can cause a blind spot in the middle of your sight line.
- Retinal Tears and Detachment. These affect the thin layer of blood vessels that supplies oxygen and nutrients to your retina. Initial symptoms are eye floaters. This condition must be treated immediately. If it isn't, it can lead to permanent vision loss.
Early detection is key to fixing problems with your sight. Don't take your eyes for granted. Get them checked regularly, and tell your doctor if you notice anything unusual.
Sources
Age Related Macular Degeneration. Bethesda, MD.: National Institute of Health, 2009. (Accessed October 18, 2009 at http://www.nei.nih.gov/health/maculardegen/index.asp.)
Vision Not Improved By Surgery for Complications of Age Related Macular Degeneration. Bethesda, MD.: National Institute of Health, 2008. (Accessed October 18, 2009 athttp://www.nei.nih.gov/news/statements/surgery_amd.asp.)
Vision Problems. Atlanta, GA.: A.D.A.M., 2008. (Accessed October 18, 2009 athttp://www.nlm.nih.gov/medlineplus/ency/article/003029.htm.)
HealthiNation offers health information for educational purposes only; this information is not meant as medical advice. Always consult your doctor about your specific health condition.
Reviewed by: Dr. Supriya Jain, Dr. Preeti Parikh and Dr. Holly Atkinson
Last Review Date: 08/29/2012
Host Reviewer: Dr. Roshini Raj
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