What is Refraction?


Refraction is the bending of light as it passes through one object to another. Vision occurs when light rays are bent (refracted) as they pass through the cornea and the lens. The light is then focused on the retina. The retina converts the light-rays into messages that are sent through the optic nerve to the brain. The brain interprets these messages into the images we see.

Refractive Error Screening

What are Refractive Errors?

In refractive errors, the shape of the eye prevents light from focusing on the retina. The length of the eyeball (longer or shorter), changes in the shape of the cornea, or aging of the lens can cause refractive errors.

HYPEROPIA - FARSIGHTNEDNESS

What is Hyperopia?

Hyperopia, also known as farsightedness, is a common type of refractive error where distant objects may be seen more clearly than objects that are near. However, people experience hyperopia differently. Some people may not notice any problems with their vision, especially when they are young. For people with significant hyperopia, vision can be blurry for objects at any distance, near or far.

hyperopia image

Causes and Risks

How does hyperopia develop?
Hyperopia develops in eyes that focus images behind the retina instead of on the retina, which can result in blurred vision. This occurs when the eyeball is too short, which prevents incoming light from focusing directly on the retina. It may also be caused by an abnormal shape of the cornea or lens.

Who is at risk for hyperopia?
Hyperopia can affect both children and adults. It affects about 5 to 10 percent of Americans. People whose parents have hyperopia may also be more likely to get the condition.

Symptoms and Detection

What are the signs and symptoms of hyperopia?
The symptoms of hyperopia vary from person to person. Your eye care professional can help you understand how the condition affects you.
Common signs and symptoms of hyperopia include:

  • Headaches
  • Eyestrain
  • Squinting
  • Blurry vision, especially for close objects

How is hyperopia diagnosed?
An eye care professional can diagnose hyperopia and other refractive errors during a comprehensive dilated eye examination. People with this condition often visit their eye care professional with complaints of visual discomfort or blurred vision.

Treatment

How is hyperopia corrected?
Hyperopia can be corrected with eyeglasses, contact lenses, or surgery.

Eyeglasses are the simplest and safest way to correct hyperopia. Your eye care professional can prescribe lenses that will help correct the problem and help you see your best.

Contact Lenses work by becoming the first refractive surface for light rays entering the eye, causing a more precise refraction or focus. In many cases, contact lenses may provide clearer vision, wider field of vision, and greater comfort. They are a safe and effective option if fitted and used properly. However, contact lenses may not be the best option for everyone.

If you certain eye conditions you may not be able to wear contact lenses. Discuss this with your eye care professional.

Refractive Surgery aims to permanently change the shape of the cornea which will improve refractive vision. Surgery can decrease or eliminate dependency on wearing eyeglasses and contact lenses. There are many types of refractive surgeries and surgical options should be discussed with an eye care professional.

MYOPIA - NEARSIGHTEDNESS

What is Myopia?
Myopia or nearsightedness, is a common type of refractive error where close objects appear clearly, but distant objects appear blurry.

Myopia image

The cornea and lens bend (refract) incoming light
rays so they focus in front of the retina.

How does nearsightedness develop?
Nearsightedness develops in eyes that focus images in front of the retina instead of on the retina, which results in blurred vision. This occurs when the eyeball becomes too long and prevents incoming light from focusing directly on the retina. It may also be caused by an abnormal shape of the cornea or lens.

Who is at risk for nearsightedness?
Nearsightedness can affect both children and adults. The condition affects about 25 percent of Americans. Nearsightedness is often diagnosed in children between 8 and 12 years of age and may worsen during the teen years. Little change may occur between ages 20 to 40, but sometimes nearsightedness may worsen with age. People whose parents are nearsighted may be more likely to get the condition.

What are the signs and symptoms of nearsightedness?
Some of the signs and symptoms of nearsightedness include:

  • Headaches
  • Eyestrain
  • Squinting
  • Difficulty seeing distant objects, such as highway signs

How is nearsightedness diagnosed?
An eye care professional can diagnose nearsightedness and other refractive errors during a comprehensive dilated eye examination. People with this condition often visit their eye care professional with complaints of visual discomfort or blurred vision.

How is nearsightedness corrected?
Nearsightedness can be corrected with eyeglasses, contact lenses, or surgery.

Eyeglasses are the simplest and safest way to correct nearsightedness. Your eye care professional can prescribe lenses that will correct the problem and help you to see your best.

Contact lenses work by becoming the first refractive surface for light rays entering the eye, causing a more precise refraction or focus. In many cases, contact lenses may provide clearer vision, wider field of vision, and greater comfort. They are a safe and effective option if fitted and used properly. However, contact lenses may not be the best option for everyone.
If you certain eye conditions you may not be able to wear contact lenses. Discuss this with your eye care professional.

Refractive surgery aims to permanently change the shape of the cornea which will improve refractive vision. Surgery can decrease or eliminate dependency on wearing eyeglasses and contact lenses. There are many types of refractive surgeries and surgical options should be discussed with an eye care professional.

PRESBYOPIA

What is presbyopia?
Presbyopia is a common type of vision disorder that occurs as you age. It is often referred to as the aging eye condition. Presbyopia results in the inability to focus up close, a problem associated with refraction in the eye.

Presbyopia Image

Can I have presbyopia and another type of refractive error at the same time?
Yes. It is common to have presbyopia and another type of refractive error at the same time. There are several other types of refractive errors: myopia (nearsightedness), hyperopia (farsightedness), and astigmatism.

An individual may have one type of refractive error in one eye and a different type of refractive error in the other.

Causes and Risk Factors

How does presbyopia occur?
Presbyopia happens naturally in people as they age. The eye is not able to focus light directly on to the retina due to the hardening of the natural lens. Aging also affects muscle fibers around the lens making it harder for the eye to focus on up close objects. The ineffective lens causes light to focus behind the retina, causing poor vision for objects that are up close.
When you are younger, the lens of the eye is soft and flexible, allowing the tiny muscles inside the eye to easily reshape the lens to focus on close and distant objects.

Who is at risk for presbyopia?
Anyone over the age of 35 is at risk for developing presbyopia. Everyone experiences some loss of focusing power for near objects as they age, but some will notice this more than others.

Symptoms and Detection

What are the signs and symptoms of presbyopia?
Some of the signs and symptoms of myopia include:

  • Hard time reading small print
  • Having to hold reading material farther than arm's distance
  • Problems seeing objects that are close to you
  • Headaches
  • Eyestrain

If you experience any of these symptoms you may want to visit an eye care professional for a comprehensive dilated eye examination. If you wear glasses or contact lenses and still have these issues, a new prescription might be needed.

How is presbyopia diagnosed?
Presbyopia can be found during a comprehensive dilated eye exam. If you notice any changes in your vision, you should visit an eye care professional. Exams are recommended more often after the age 40 to check for age-related conditions.

Treatment

How is presbyopia corrected?
Eyeglasses are the simplest and safest means of correcting presbyopia. Eyeglasses for presbyopia have higher focusing power in the lower portion of the lens. This allows you to read through the lower portion of the lens and see properly at distant through the upper portion of the lens. It is also possible to purchase reading eyeglasses. These types of glasses do not require a prescription and can help with reading vision.

ASTIGMATISM

What is astigmatism?
Astigmatism is a common type of refractive error. It is a condition in which the eye does not focus light evenly onto the retina, the light-sensitive tissue at the back of the eye.

Astigmatism image

Causes and Risk Factors

How does astigmatism occur?
Astigmatism occurs when light is bent differently depending on where it strikes the cornea and passes through the eyeball. The cornea of a normal eye is curved like a basketball, with the same degree of roundness in all areas. An eye with astigmatism has a cornea that is curved more like a football, with some areas that are steeper or more rounded than others. This can cause images to appear blurry and stretched out.

Who is at risk for astigmatism?
Astigmatism can affect both children and adults. Some patients with slight astigmatism will not notice much change in their vision. It is important to have eye examinations at regular intervals in order to detect any astigmatism early on for children.

Symptoms and Detection

What are the signs and symptoms of astigmatism?
Signs and symptoms include:

  • Headaches
  • Eyestrain
  • Squinting
  • Distorted or blurred vision at all distances
  • Difficulty driving at night

If you experience any of these symptoms, visit your eye care professional. If you wear glasses or contact lenses and still have these issues, a new prescription might be needed.

How is astigmatism diagnosed?
Astigmatism is usually found during a comprehensive dilated eye exam. Being aware of any changes in your vision is important. It can help in detecting any common vision problems. If you notice any changes in your vision, visit your eye care professional for a comprehensive eye dilated examination.

Can you have astigmatism and not know it?
It is possible to have mild astigmatism and not know about it. This is especially true for children, who are not aware of their vision being other than normal. Some adults may also have mild astigmatism without any symptoms. It's important to have comprehensive dilated eye exams to make sure you are seeing your best.

Treatment

How is astigmatism corrected?
Astigmatism can be corrected with eyeglasses, contact lenses, or surgery. Individual lifestyles affect the way astigmatism is treated.

Eyeglasses are the simplest and safest way to correct astigmatism. Your eye care professional will prescribe appropriate lenses to help you see as clearly as possible.

Contact Lenses work by becoming the first refractive surface for light rays entering the eye, causing a more precise refraction or focus. In many cases, contact lenses provide clearer vision, a wider field of vision, and greater comfort. They are a safe and effective option if fitted and used properly. It is very important to wash your hands and clean your lenses as instructed in order to reduce the risk of infection.
If you certain eye conditions you may not be able to wear contact lenses. Discuss this with your eye care professional.

Refractive Surgery aims to change the shape of the cornea permanently. This change in eye shape restores the focusing power of the eye by allowing the light rays to focus precisely on the retina for improved vision. There are many types of refractive surgeries. Your eye care professional can help you decide if surgery is an option for you.


The National Eye Institute (NEI) is part of the National Institutes of Health (NIH) and is the Federal government's lead agency for vision research that leads to sight-saving treatments and plays a key role in reducing visual impairment and blindness.