ametropia

The cornea and lens of your eye helps you focus. Refractive errors are vision problems that happen when the shape of the eye keeps you from focusing well. The cause could be the length of the eyeball (longer or shorter), changes in the shape of the cornea, or aging of the lens.

Four common refractive errors are:

• Myopia, or nearsightedness - clear vision close up but blurry in the distance
• Hyperopia, or farsightedness - clear vision in the distance but blurry close up
• Presbyopia - inability to focus close up as a result of aging
• Astigmatism - focus problems caused by the cornea

The most common symptom is blurred vision. Other symptoms may include double vision, haziness, glare or halos around bright lights, squinting, headaches, or eye strain.

Glasses or contact lenses can usually correct refractive errors. Laser eye surgery may also be a possibility.

NIH: National Eye Institute

Amblyopia, or "lazy eye," is the most common cause of visual impairment in children. It happens when an eye fails to work properly with the brain. The eye may look normal, but the brain favors the other eye. In some cases, it can affect both eyes. Causes include:

• Strabismus - a disorder in which the two eyes don't line up in the same direction
• Refractive error in an eye - when one eye cannot focus as well as the other, because of a problem with its shape. This includes nearsightedness, farsightedness, and astigmatism.
• Cataract - a clouding in the lens of the eye

It can be hard to diagnose amblyopia. It is often found during a routine vision exam.

Treatment for amblyopia forces the child to use the eye with weaker vision. There are two common ways to do this. One is to have the child wear a patch over the good eye for several hours each day, over a number of weeks to months. The other is with eye drops that temporarily blur vision. Each day, the child gets a drop of a drug called atropine in the stronger eye. It is also sometimes necessary to treat the underlying cause. This could include glasses or surgery.

NIH: National Eye Institute

Your cornea is the outermost layer of your eye. It is clear and shaped like a dome. The cornea helps to shield the rest of the eye from germs, dust, and other harmful matter. It also helps your eye to focus. If you wear contact lenses, they float on top of your corneas.

Problems with the cornea include:

• Refractive errors
• Allergies
• Infections
• Injuries
• Dystrophies - conditions in which parts of the cornea lose clarity due to a buildup of cloudy material

Treatments of corneal disorders include medicines, corneal transplantation, and corneal laser surgery.

NIH: National Eye Institute

Your eyes are an important part of your health. Most people rely on their eyes to see and make sense of the world around them. But some eye diseases can lead to vision loss, so it is important to identify and treat eye diseases as early as possible. You should get your eyes checked as often as your health care provider recommends it, or if you have any new vision problems. And just as it is important to keep your body healthy, you also need to keep your eyes healthy.

There are things you can do to help keep your eyes healthy and make sure you are seeing your best:

• Eat a healthy, balanced diet. Your diet should include plenty or fruits and vegetables, especially deep yellow and green leafy vegetables. Eating fish high in omega-3 fatty acids, such as salmon, tuna, and halibut can also help your eyes.
• Maintain a healthy weight. Being overweight or having obesity increases your risk of developing diabetes. Having diabetes puts you at higher risk of getting diabetic retinopathy or glaucoma.
• Get regular exercise. Exercise may help to prevent or control diabetes, high blood pressure, and high cholesterol. These diseases can lead to some eye or vision problems. So if you exercise regularly, you can lower your risk of getting these eye and vision problems.
• Wear sunglasses.Sun exposure can damage your eyes and raise your risk of cataracts and age-related macular degeneration. Protect your eyes by using sunglasses that block out 99 to 100% of both UV-A and UV-B radiation.
• Wear protective eye wear. To prevent eye injuries, you need eye protection when playing certain sports, working in jobs such as factory work and construction, and doing repairs or projects in your home.
• Avoid smoking. Smoking increases the risk of developing age-related eye diseases such as macular degeneration and cataracts and can damage the optic nerve.
• Know your family medical history. Some eye diseases are inherited, so it is important to find out whether anyone in your family has had them. This can help you determine if you are at higher risk of developing an eye disease.
• Know your other risk factors. As you get older, you are at higher risk of developing age-related eye diseases and conditions. It is important to know you risk factors because you may be able to lower your risk by changing some behaviors.
• If you wear contacts, take steps to prevent eye infections. Wash your hands well before you put in or take out your contact lenses. Also follow the instructions on how to properly clean them, and replace them when needed.
• Give your eyes a rest. If you spend a lot of time using a computer, you can forget to blink your eyes and your eyes can get tired. To reduce eyestrain, try the 20-20-20 rule: Every 20 minutes, look away about 20 feet in front of you for 20 seconds.

Everyone needs to have their eyesight tested to check for vision and eye problems. Children usually have vision screening in school or at their health care provider's office during a checkup. Adults may also get vision screenings during their checkups. But many adults need more than a vision screening. They need a comprehensive dilated eye exam.

Getting comprehensive dilated eye exams is especially important because some eye diseases may not have warning signs. The exams are the only way to detect these diseases in their early stages, when they are easier to treat.

The exam includes several tests:

• A visual field test to measure your side (peripheral) vision. A loss of peripheral vision may be a sign of glaucoma.
• A visual acuity test, where you read an eye chart about 20 feet away, to check on how well you see at various distances
• Tonometry, which measures your eye's interior pressure. It helps to detect glaucoma.
• Dilation, which involves getting eye drops that dilate (widen) your pupils. This allows more light to enter the eye. Your eye care provider examines your eyes using a special magnifying lens. This provides a clear view of important tissues at the back of your eye, including the retina, macula, and optic nerve.

If you have a refractive error and are going to need glasses or contacts, then you will also have a refraction test. When you have this test, you look through a device that has lenses of different strengths to help your eye care professional figure out which lenses will give you the clearest vision.

At what age you should start getting these exams and how often you need them depends on many factors. They include your age, race, and overall health. For example, if you are African American, you are at higher risk of glaucoma and you need to start getting the exams earlier. If you have diabetes, you should get an exam every year. Check with your health care provider about if and when you need these exams.

Some eye problems are minor and don't last long. But some can lead to a permanent loss of vision.

Common eye problems include:

• Refractive errors
• Cataracts - clouded lenses
• Optic nerve disorders, including glaucoma
• Retinal disorders - problems with the nerve layer at the back of the eye
• Macular degeneration - a disease that destroys sharp, central vision
• Diabetic eye problems
• Conjunctivitis - an infection also known as pink eye

Your best defense is to have regular checkups, because eye diseases do not always have symptoms. Early detection and treatment could prevent vision loss. See an eye care professional right away if you have a sudden change in vision, if everything looks dim, or if you see flashes of light. Other symptoms that need quick attention are pain, double vision, fluid coming from the eye, and inflammation.

NIH: National Eye Institute

Eye wear protects or corrects your vision. Examples are:

• Sunglasses
• Safety goggles
• Glasses (also called eyeglasses)
• Contact lenses

If you need corrective lenses, you may be able to choose between contacts or glasses. Either usually requires a prescription. Almost anyone can wear glasses. Contact lenses require more careful handling.

Many jobs and some sports carry a risk of eye injury. Thousands of children and adults get eye injuries every year. Most are preventable with proper eye protection. Everyone is at risk for eye damage from the sun year-round. It's important to regularly use sunglasses that block out at least 99% of UV rays.

For many people, laser eye surgery can correct their vision so they no longer need glasses or contact lenses. Laser eye surgery reshapes the cornea, the clear front part of the eye. This changes its focusing power.

There are different types of laser eye surgery. LASIK - laser-assisted in situ keratomileusis - is one of the most common. Many patients who have LASIK end up with 20/20 vision. But, like all medical procedures, it has both risks and benefits. Only your eye doctor can tell if you are a good candidate for laser eye surgery.