Stronger glasses every year? See where your child's myopia is heading.

In children wearing ordinary single-vision glasses, a 2012 review of 20 studies found an average change of about 0.55 diopters a year at age 9 for children of European ancestry and 0.82 for Asian children. Younger children change faster, and girls slightly faster than boys.

In the COMET study, which followed 469 children for up to 11 years, myopia stopped climbing at 15.6 years of age on average, at an average of –4.87. The spread is wide: some children settle in their early teens, others keep changing into their twenties.

It sits in the middle of the published range for children in ordinary glasses. What it adds up to depends on age: half a diopter a year from age 7 is a very different total by 16 than the same pace from age 13. The tool above does that arithmetic.

Myopia control is the name optometrists use for anything meant to slow the yearly climb: special spectacle lenses, soft multifocal contact lenses, overnight lenses (orthokeratology), low-dose atropine drops, and more time outdoors. It is judged by how much it lowers the yearly change compared with ordinary glasses.

Studies across many countries find that children who spend more time outdoors become nearsighted less often. Daylight appears to be what matters, not exercise. The effect on myopia that has already started is smaller and less consistent.

Regular eye exams are part of tracking the yearly number. See a licensed professional promptly for a sudden drop in vision, one eye turning in or out, pain, flashes, new floaters, or a child who squints or covers one eye to see.