How do I know if my child needs glasses?

Adult patients can sit at a phoropter to have their refractive error -- need for glasses -- measured.

If your child doesn’t seem to see well — whether they are holding things very close to see them, or complaining that their vision is blurry, or if something just seems “off” — bring them in for an eye exam!

Determining whether glasses are needed is part of any complete eye exam, and includes measurements of a child’s current visual abilities as well as their “refractive error.”

What is “refractive error,” you ask? Well, it’s the medical term for how “out of focus” the eyes are. Our eyes have a tremendous ability to focus, but it is rarely perfect. Most everyone has some degree of refractive error as a result. For the majority of people, this “out of focus” is minimal and not enough to need glasses. For others, it is enough to make vision blurry, and glasses are needed. Of course, not every eye problem is due to refractive error, so glasses don’t fix every possible type of eye problem.

The cool thing about refractive error is that, like a shoe size, it can be measured, even for kids who aren’t old enough to cooperate very well or even speak!

Unlike adults, who can easily sit behind a device called a phoropter (see photo) and reliably tell you whether "Number 1 is clearer" or "Number 2 is clearer," children have their glasses prescription measured in a different way.

By using a handheld device called a retinoscope, the eye doctor can accurately measure not only whether a child needs glasses, but also what the prescription should be.

The physician turns on the retinoscope, generating a bar of light, and then looks at each eye, moving the bar of light up and down and side to side. This creates a reflex of light within the patient's eye. Handheld lenses -- just like the ones in the dials of the phoropter -- are held up in front of the patient's eye, and the physician looks for the light reflex to stop moving as he or she moves the bar of light. The lenses that allow this light reflex to stop moving are used to determine the patient's prescription. In the hands of an experienced examiner, this method of prescribing glasses is very accurate.

A standard retinoscope, used to measure glasses prescriptions in children.