Diagnosing Refractive Error

Ophthalmologists and optometrists at NYU Langone diagnose refractive errors in adults and children after performing a comprehensive eye exam. This exam takes place in a doctor’s office and is not uncomfortable, although some tests—for example, those that use eyedrops that widen your pupils—may make your eyes feel a bit strange and blur your vision for an hour or two. 

Our eye doctors recommend having an eye exam if you experience blurred vision. You should also have your eyes examined if you find yourself frequently squinting or straining to see objects that are far away, such as street signs, or up close, such as text in a book or on a computer screen. 

In children, common symptoms of refractive error include not being able to see learning materials at the front of a classroom or difficulty reading, which may indicate an inability to see text up close. Squinting and straining can cause headaches. Children may also be observed repeatedly rubbing their eyes while reading or watching TV if they have trouble seeing clearly.

Our doctors examine people of all ages and diagnose refractive error after performing an eye exam. Children receive diagnosis of refractive error through Hassenfeld Children’s Hospital at NYU Langone.

Medical History

Your doctor asks a variety of questions about your eyesight and overall health as part of an eye exam. For example, an eye doctor may ask whether you have trouble seeing objects that are far away, close up, or both, and when you first started to notice that your vision was sometimes blurry.

He or she may also ask if anyone else in your family wears glasses or contact lenses or has been diagnosed with another eye condition, such as glaucoma, which leads to damage of the nerve that connects the eye to the brain, or cataract, which clouds the lens of the eye. People who have a refractive error—especially myopia—may be at an increased risk of developing these conditions. In some instances, diabetes may also cause refractive error if not managed properly. 

Occasionally, the changes in hormones, metabolism, and blood circulation that occur during pregnancy can cause a change in vision. Women may find that they become slightly nearsighted or farsighted while pregnant and nursing. Vision almost always shifts back to normal after the baby is born or after a woman has stopped breastfeeding. 

Eye doctors recommend an eye exam early in pregnancy to ensure that any changes in the eye are minor and don’t require medical attention. Women who develop gestational diabetes, a form of diabetes that occurs during pregnancy, should have routine eye exams while pregnant.

Eye and Vision Tests

Your eye doctor performs a series of painless tests to evaluate your vision as well as the overall health of your eyes. Based on the results of these tests, he or she can determine the type of refractive error affecting your vision and recommend treatment with either corrective lenses or surgery.

Visual Acuity Testing

A visual acuity test assesses how well you can see at a standardized distance. Eye doctors have determined what “normal” vision is when reading at this distance and compare this with your vision.

To conduct the test, your doctor uses an eye chart positioned 20 feet away that displays rows of letters in increasingly smaller sizes. Your doctor asks you to read as many of the lines as you can without squinting, sometimes while covering one eye. If you can see all of the letters clearly, you are considered to have 20/20 vision. 

The doctor may also ask you to read a few lines from a preprinted card or sheet of newspaper. This simple test gives the specialist information about how well you can see close up and helps to confirm a diagnosis of refractive error.

Corneal Topography

If your doctor notices anything unusual about the shape of your cornea, the outermost layer of the eye, he or she may use corneal topography to map the surface of this area.

To conduct this painless test, your doctor asks you to rest your chin and forehead against an instrument with a bowl-shaped indentation and look at the illuminated pattern displayed in the bowl. A digital camera located in the center of the bowl captures the way this pattern is reflected off your cornea.

This information is sent to a computer that converts it to a three-dimensional image of your eye. Corneal topography can help doctors measure the shape of your eyes for contact lens fitting or to guide a doctor’s approach during laser surgery. 

After your doctor has completed the eye exam, he or she provides you with a prescription that indicates the type of refractive error you are diagnosed with, the lens power required to correct your vision, and whether your right and left eyes have different corrective needs. This prescription can be for eyeglasses or contact lenses, based on your preference.