ametropia

The cornea and lens of your eye bend (refract) light rays to focus them on the retina. Refractive errors happen when the shape of your eye prevents light from focusing correctly on the retina. This causes blurry vision. Changes in the eye's shape affect how light rays bend and focus, leading to vision problems.

Refractive errors can happen when:

• The eyeball is too long or too short.
• The cornea changes shape.
• The lens becomes less flexible as you age.

Each type of refractive error is different, but they all make it hard to see clearly.

Four common types of refractive errors include:

• Nearsightedness (myopia), blurred vision when looking at faraway objects.
• Farsightedness (hyperopia), blurred vision when looking at close-up objects.
• Astigmatism, blurred or distorted vision at all distances, which can make night vision harder.
• Presbyopia, difficulty seeing things up close because the lens becomes less flexible with age. It affects adults in middle age and older and often begins around age 45.

Anyone can have refractive errors. It's the most common type of vision problem. You may be more likely to have one if other family members wear glasses or contact lenses.

Most types of refractive errors start in childhood or are present at birth. Presbyopia is different. Nearly everyone develops it as they age, typically starting around age 45.

Sometimes you may not notice vision changes right away, which is why regular eye exams are so important.

The most common symptom is blurred vision. Other symptoms may include:

• Double vision
• Haziness
• Glare or halos around bright lights
• A need to squint to see clearly
• Headaches
• Eye strain or tired eyes
• Difficulty focusing when reading or using a computer

If you already wear glasses or contact lenses and notice these symptoms, you may need a new prescription. Tell your eye care specialist if your vision changes or if you have problems with your glasses or contact lenses

An eye care specialist can diagnose refractive errors during a comprehensive eye exam. You'll be tested to see how well you can see at different distances, both with and without corrective lenses (glasses or contact lenses). Your provider may also use special eye drops to dilate (widen) your pupils to check for other eye conditions.

Different eye care specialists may be involved in your care. Here are some of the most common:

• Ophthalmologists are medical doctors who treat eye diseases, prescribe glasses or contact lenses, and perform eye surgery.
• Optometrists perform eye exams, diagnose vision problems, and prescribe glasses or contact lenses.
• Opticians fit or adjust glasses or contact lenses based on a prescription from your eye care specialist.

Refractive errors are usually easy to correct with:

• Glasses
• Contact lenses
• Laser eye surgery, in some cases

Your eye care specialist can help choose the best treatment for your vision and lifestyle.

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

Eye care is about keeping your eyes healthy through good daily habits, regular checkups, and treatment when needed. Your eyes are an important part of your health. You rely on them every day to see and understand the world around you. Some eye diseases can lead to vision loss without early warning signs, so it's important to catch them as soon as possible. Get your eyes checked as often as your health care provider recommends, or if you notice new vision problems. Just like caring for the rest of your body, it's important to keep your eyes healthy.

There are many things you can do to protect your eyes and see your best:

• Give your eyes a rest. Spending long hours on a computer or other digital screens can make you blink less, causing dryness and tired eyes. To reduce eyestrain, try the 20-20-20 rule: Every 20 minutes, look away about 20 feet in front of you for 20 seconds.
• 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 eyewear. 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 rubbing your eyes. Rubbing your eyes can transfer dirt and bacteria that may cause irritation or lead to an infection.
• Use good lighting. Brighten your space to reduce strain and help you see comfortably.
• If you wear contacts, take steps to prevent eye infections. Wash your hands 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.

What you eat and how you take care of your body can have a big impact on your eyes and vision:

• Eat a healthy, balanced diet. Your diet should include plenty of fruits and vegetables, especially dark leafy green vegetables like spinach, kale, or collard greens. 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. Regular exercise helps lower your risk.
• 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 (passed down through families), 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 your risk factors because you may be able to lower your risk by changing some behaviors.

Everyone needs their eyesight tested to check for vision and eye problems. Children usually have vision screening, also called an eye test, in school or at their provider's office during a checkup. This is a brief test that mainly checks how well you can see things up close and far away. 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 eye exam includes several tests:

• Test your side (peripheral) vision with a visual field test. Losing peripheral vision may be a sign of glaucoma.
• Check how well you see at various distances with a visual acuity test, where you read an eye chart about 20 feet away.
• Follow an object with your eyes during an eye muscle function test to check for problems with the muscles that control your eyes.
• Shine a light into your eyes with a pupil response test to see how your pupils react to light.
• Measure the pressure inside your eyes with tonometry. This test helps to detect glaucoma.
• Dilate (widen) your pupils with special eye drops allows more light to enter the eye. Your eye care provider then uses a special magnifying lens to clearly see 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.

How often you need eye exams depends on your age, race, risk factors, and overall health. For example, Black/African American adults are at higher risk for glaucoma and may need to start exams earlier. If you have diabetes, you should have an exam every year. Check with your provider about when you need these exams.

See an eye care specialist right away if you have symptoms like sudden loss of vision, double vision, blurred vision with eye pain, flashes of light, black spots or halos around lights. These symptoms may represent a serious medical or eye condition.

Even if your eyes feel healthy, you could have a problem and not know it. That's why regular eye exams are so important. Refractive errors are the most common type of vision problem that makes it hard to see clearly. But some eye conditions or diseases don't have any symptoms and can lead to a permanent loss of vision.

Some common eye diseases and conditions include:

• Cataracts, which happens when the clear lens in the front of your eye becomes cloudy. Cataracts are common as you get older and can lead to vision loss.
• Optic nerve disorders, which includes glaucoma. Glaucoma usually happens when the fluid pressure inside your eyes slowly rises.
• Retinal disorders, which are problems with the nerve layer at the back of your eye.
• Macular degeneration, which is a disease that destroys your sharp, central vision.
• Diabetic eye problems, which can cause vision loss and blindness.
• Conjunctivitis, which is an infection also known as pink eye. It can cause pink or red itchy eyes. Some types of pink eye can spread very easily.

Some eye conditions and diseases do not always have symptoms. Early detection through a comprehensive dilated eye exam could help your eye care provider detect diseases in the early stages. Proper treatment could help slow or prevent vision loss.

Get regular eye exams and call your eye care professional right away if you notice any of these symptoms:

• A sudden change in vision
• Everything looks dim
• Flashes of light
• Eye pain
• Double vision
• Fluid coming from your eye
• Inflammation (swelling)

Getting older increases your risk of some eye diseases. Other things that may put you at a higher risk of some eye diseases can include if you:

• Are overweight or obese
• Have a family history of eye disease
• Are African American, Hispanic, or Native American
• Have certain health conditions such as Diabetic eye problems, or high blood pressure

Treatment may depend on the eye condition or disease but can include:

• A new prescription for eyeglasses or contacts
• Use of bright lights or magnifying lenses for reading and other activities
• Medicines
• Prescription eye drops or ointments
• Laser treatment
• Surgery

Depending on your eye condition or disease, treatment may slow vision loss but may not restore vision. Talk to your provider about what treatment is best for you.

Your best defense is to have regular checkups. Be sure to tell your provider if any eye diseases run in your family.

You can also help take care of your vision by making lifestyle changes to lower your risk of health conditions that can cause vision problems. This could include by:

• Protecting your eyes from the sun
• Wearing protective eyewear while using tools or playing certain sports
• Getting regular physical activity
• Staying at a healthy weight
• Quitting smoking (or not starting)
• Eating a healthy diet

NIH: National Eye Institute

Eyewear 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.