How Do We See?

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Astigmatism: a defect of the eye (usually involving the lens) that causes blurry vision.

Hyperopia: also called farsightedness; a condition caused by short eyes and corneas that curve too little; a person with hyperopia will have a difficult time clearly seeing objects close to them...more

Myopia: also called nearsightedness; a condition caused by long eyes and stretched corneas; a person with myopia will have difficulty seeing objects that are far away.

Opthamologist: a medical doctor who can test vision, give patients prescriptions for glasses or contact lenses, or perform surgery to fix problems associated with the eye.

Optometrist: a medical professional who can test vision and give a prescription for glasses or contact lenses.

Do You Need Glasses?

You squint your eyes, lean forward a bit, and close one eye. You open that eye, close the other, squint again, and pull your head back. No matter what you seem to do, the sign still looks blurry. Did someone make a blurry sign? Or might you need glasses? Lots of people have problems with vision that can be corrected with glasses or contact lenses. To get these, you should visit the eye doctor.

Vision chart

A typical eye chart. Click for more detail.

There are two types of vision experts that you can see to have your eyes checked. An optometrist has special training to examine eyes and can give prescriptions for glasses and contact lenses. An ophthalmologist is a doctor who, in addition to checking your eyes and giving prescriptions for glasses and contact lenses, can also perform surgeries to fix eyes that have been injured.

Some people go to an eye doctor each year to check that their eyes are healthy. During an exam, the eye doctor will usually ask a patient if they have any trouble seeing things up close, far away, and when it is dark. The doctor might also take a picture of the inside of a patient’s eye by having them look into some fancy binoculars. This picture is called a retinal scan and lets the eye doctor see the retina and check that the blood vessels and tissue look healthy. During the next part of the exam the patient will be asked to look at an eye chart and to cover one of their eyes to see how well they can read the letters with the uncovered eye. How does this let them know that the patient needs glasses?

Near Sightedness

Myopic simulation

People with myopia can only focus on items closer to them. Click for more detail.

A person who has good vision when viewing something up close, but blurry vision when viewing something far away, is probably near sighted. What does “Near Sighted” actually mean? Near sightedness, or “Myopia,” is a condition that occurs when the eye has a long shape or the cornea is too curved.

This causes light to enter the eye and create an image in front of the retina. To treat this problem, the eye doctor will need to prescribe glasses that will refocus the light onto the retina and not in front of it.

Far Sightedness

A person who can clearly see objects that are far away, but cannot read print on a page that is close to their eyes, is likely far sighted. Far sightedness, or “Hyperopia,” is a condition that occurs when the eye is short or the cornea curves too little. The image that is projected into the eye would be in focus behind the retina. In order to see in focus, the eye doctor will need to prescribe glasses that refocus the light onto the retina and not behind it.

Astigmatism

Astigmatism

An image showing astigmatism. Click for more detail.

Occasionally there can be something wrong with the lenses in the eye. If the lenses are not smooth or extra thick or thin in some areas, this will change the way that the image is projected into the eye. This is called astigmatism.

If the image does not lay flat on the retina then the final picture that the brain sees will be blurry in spots. Special lenses can be designed so that light coming into the eye will focus correctly on the retina.


Additional images via Wikimedia Commons.

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Bibliographic details:

  • Article: Do You Need Glasses?
  • Author(s): Page Baluch, Ashleigh Gonzales
  • Publisher: Arizona State University School of Life Sciences Ask A Biologist
  • Site name: ASU - Ask A Biologist
  • Date published: July 1, 2015
  • Date accessed:
  • Link: https://askabiologist.asu.edu/fr/do-you-need-glasses

APA Style

Page Baluch, Ashleigh Gonzales. (2015, July 01). Do You Need Glasses?. ASU - Ask A Biologist. Retrieved from https://askabiologist.asu.edu/fr/do-you-need-glasses

American Psychological Association. For more info, see http://owl.english.purdue.edu/owl/resource/560/10/

Chicago Manual of Style

Page Baluch, Ashleigh Gonzales. "Do You Need Glasses?". ASU - Ask A Biologist. 01 July, 2015. https://askabiologist.asu.edu/fr/do-you-need-glasses

MLA 2017 Style

Page Baluch, Ashleigh Gonzales. "Do You Need Glasses?". ASU - Ask A Biologist. 01 Jul 2015. ASU - Ask A Biologist, Web. . https://askabiologist.asu.edu/fr/do-you-need-glasses

Modern Language Association, 7th Ed. For more info, see http://owl.english.purdue.edu/owl/resource/747/08/
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