How do they test toddlers vision?

I often see very small children (1.5-2.5 years old) wearing eyeglasses and wonder what kind of tests they administer to them.
Since they can’t talk yet how do they get responses to the usual “which is sharper, A or B” or get them to read an eye chart?

IIRC, the use the letter E. It can be oriented so that the three bars are up, down, left, or right (the usual orientation) and you ask the child which way the bars point.

They can use pictures too, and as questions like “what’s this a picture of?” or “which one of these is a horse?”

My son had his eyes checked before he knew his letters. Since the doctor watched him watch TV, I’m guessing he just wanted to see how he focused on anything rather than what that thing actually was.

Pediatric ophthalmologists are amazing. They use dilation and “test lenses” to measure how light passes through the cornea to the retina. Our Peds Dr. is a very sweet, VERY petite, attractive woman, who is absolutely unscary to the little patients. She’s also very good with the special needs community, including nonverbal adults. My son is almost 14, completely nonverbal (and noncompliant) and she checks his eyes.

Littlest baby I ever fit for glasses was 4 months old. I still see him a few times a year, and his prescription gets a little less severe each time. I’m pretty sure he’s had some surgery too. He’s 5 now.

What I remember about my pre-literate eye tests (glasses since age 2), the doc would do the pictures thing then give me a sedative to put me out. Obviously, I don’t remember what happened until I woke up at home a couple of hours later.

Of course, this was 40+ years ago and things might have changed since then.

When I was little they would have the letter E pointed in different directions. I would than use my first thing fingers to tell the doctor which way the E was pointing. As I got older it seems they have changed the sign. They now use pictures. The only one I can remember off hand is a sailboat

They can test babies by showing them 2 pictures, one of a single color and one of a bunch of wavy lines that look like the single color if the picture is held far enough away. Under those circumstances, the baby can be expected to look at both pictures equally. If they gradually bring the pictures closer and closer, eventually the baby recognizes that the picture with the wavy lines is, well, a picture with wavy lines. Since even newborns prefer to look at patterns vs. a solid color, the baby will start looking at the wavy lines picture more. The point at which the baby starts preferring the wavy lines picture tells the tester how good the baby’s eyesight is. If memory serves, a newborn’s eyesight is about 20/200. However, it starts getting better immediately; improvements can be measured in mere hours.

We had our daughter’s eyes checked at six months of age.* The optometrist used what looked like the test lenses WishIHadACoolName referred to, and drops to dilate her eyes. I think she was just making sure that eye control and object-following was appropriate for the age, and was also checking focus on the retina.

    • While I was getting my own eye exam, I asked the doctor when she recommended kids be checked out. Her reply surprised me: First exam at six months, another at three years, and then one right before starting school.

I participate in school vision screenings, often at Head Start programs. Retinoscopy is a tool that works on children (and adults) to give an objective value of the refractive state of their eyes:
http://en.wikipedia.org/wiki/Retinoscopy
We use Lea charts, which have shapes, so the kids just have to say “square” or “circle” or “apple” or what have you. Nearpoint vision tests work the same way.

It’s still tricky to prescribe glasses to children. They often have substantial refractive errors that will disappear in the next few years. I’m not by any means an expert on this (though hopefully I’ll have some more knowledge by the time I graduate!) but conventional wisdom is that at a young age, low refractive errors aren’t too much of a problem, so long as they are equal in both eyes. Research shows even one diopter of difference in hyperopic (that is, far-sightedness) refractive error in a child can lead to development of amblyopia if uncorrected.