The US Preventive Services Task Force recently recommended vision screening for all children between the ages of three and five.

If you’ve logged a good amount of time trying to distinguish “C” from “O,” you might be wondering how your three-year-old could possibly sit still for an eye exam, let alone read one.

Childhood vision screening generally takes place in a pediatrician’s office. Here’s what your child’s pediatrician is looking for and what you can expect during the visit.

What your child’s pediatrician is looking for

Unlike your eye exams, which may include testing for glasses, your child’s vision screenings are generally looking for warning signs of future vision problems.

Your child’s pediatrician is specifically screening for evidence of amblyopia, which occurs when one eye is unable to communicate properly with the brain. The risk of amblyopia is low: according to the USPSTF, between one and six percent of kids under age six will have either amblyopia of a risk factor for amblyopia.

In its review, the USPSTF found there to be small but permanent improvements to vision in three- to five-year-olds when amblyopia is identified and treated. Because the tests for amblyopia and its risk factors are non-invasive, the USPSTF has determined that the benefits of vision screening outweigh any harms.

What to expect during the visit

A pediatrician may use many different tools to examine your child’s eye structure, coordination, and acuity. The following three tests are among the most common.

Tool 1: Red Reflex

What it measures: Your child has likely had a red reflex test before, as many kids have them before two months of age. The test helps identify any physical abnormalities in the back of the eye, ranging from cataracts to retinoblastoma.

The red reflex test is named after the color healthy eyes give off when viewed through an ophthalmoscope from about one foot away. That red color is easier to see in the dark, which is why your pediatrician may turn the lights off for this test.

The phenomenon is the same as the “red eye” you try to edit out of photographs. In fact, photographs featuring a single red eye have been used to identify serious eye conditions.

Tool 2: Cover/Uncover Test

What it measures: You’ve probably seen your child’s pediatrician do a fix and follow test, in which your child is instructed to look at the pediatrician’s finger and follow it around the room. That test examined how well your child’s eyes function together.

The cover/uncover test works a similar way. Your child will be asked to focus on an object in the distance, then the pediatrician will cover one of your child’s eyes. While your child is still looking at the object, the tester will uncover the eye and watch for movement.

The test is observing for strabismus (incorrectly aligned eyes), which is one risk factor for amblyopia.

Tool 3: Lea Symbols Chart

What it measures: You may have not spent a lot of time thinking about how the letters at your optometrist office get made. They are optotypes, specially designed tools for testing vision. The letters in an optotype are designed to all blur equally under the same conditions, which give examiners a better understanding of a patient’s visual acuity.

Pre-readers get their own special optotypes. Instead of letters, they’ll likely have four symbols: a square, a circle, a house, and an apple. Those symbols, called the Lea Symbols, have been shown to get more cooperation from kids than other eye tests.

The Lea Symbols test works much like the eye charts you see (or don’t see!) at your optometrist. The test measures kids’ visual acuity, and can determine whether or not your child may need glasses.