How much should a child's eye power increase each year?

When a child’s glasses get stronger at every visit, the question every parent asks is the same: is this normal, or is it rising too fast? It is the right thing to ask, because the rate of change matters more than any single number. Here is how to read it.

First, why it rises at all

Short-sight (myopia) in children rises because the eyeball is growing slightly too long as the child grows. It isn’t caused by reading in dim light, watching TV, or “weak eyes,” and it can’t be reversed by food or exercise. The eye lengthens, the number goes up. The aim of treatment is not to shrink it back, it is to slow how fast it lengthens.

So how much change is “normal”?

There is no single textbook figure. As a rough guide:

• A change of around -0.50 dioptre a year is common and fairly typical in a growing, short-sighted child.
• Around -0.75 to -1.00 a year is a faster pace that’s worth watching closely.
• More than -1.00 a year, or jumps that keep getting bigger, is fast progression, and the situation where acting early matters most.

Two caveats. Younger children (say 6–9) tend to progress faster than teenagers, so the same number means more in a younger child. And the glasses prescription is a slightly blunt tool, which is why it is not relied on alone.

The better measurement: axial length

The glasses number can wobble visit to visit. A more direct measure is axial length, the length of the eyeball, measured on an optical biometer. It shows whether the eye is still growing too fast, and whether treatment is working. Each measurement is compared to the last.

Why the rate matters so much

It isn’t about vanity or thicker glasses. A higher final power in adulthood carries a higher lifelong risk of serious eye problems, including retinal detachment and earlier glaucoma. Every dioptre prevented lowers that risk. The aim of slowing progression is not to remove the glasses, but to protect the eye long term.

When to act

Have your child assessed by an eye doctor if:

• Their power has risen two years running, or jumped noticeably in one year.
• They were under 10 when they first needed glasses.
• Short-sight runs in the family (one or both parents).

If fast progression is confirmed, low-dose atropine drops, myopia-control lenses and daily outdoor time can slow it in many children. Results vary. If it is not progressing fast, monitoring alone is usually enough.