By Dr. Mark Page · · 4 min read
This is the conversation I have most often, and it is the reason I ended up writing a book for parents. It goes like this. A parent brings a child in for their annual exam. The prescription has gone up again, for the third year running. The parent asks whether that is normal, and the honest answer is yes.
And then the conversation usually stops, because normal sounds like reassurance. It is not. Normal and harmless are different words, and the gap between them is where the useful information lives.
What is actually happening
Nearsightedness is not a weakness in the eye. It is a shape problem. A myopic eye has grown too long from front to back, so light entering it comes to a focus slightly in front of the retina rather than on it. Distant things blur. Near things stay clear, because near light focuses further back.
Each year that the eye grows a little longer, the prescription gets a little stronger. That is all a rising prescription means. The lens in front of the eye is compensating for a physical dimension that keeps changing.
The eye stops growing in the late teens for most people, and wherever the prescription is at that point is roughly where it stays.
Why the final number matters
Here is the part that rarely gets explained. The retina lining the back of the eye has to stretch to cover a larger eye. Stretched retinal tissue is thinner and more fragile, and that is the mechanism behind essentially every long-term risk associated with high myopia.
The risk is not a cliff at some threshold. It is a slope, rising with each additional dioptre. That is genuinely good news, because it means any amount of slowing produces a real reduction in lifetime risk. Halving the rate of progression does not merely delay the problem, it changes where your child ends up.
An adult who finishes at minus two and an adult who finishes at minus six do not have the same eyes. They have different lifetime probabilities of retinal detachment, of glaucoma, and of myopic macular degeneration, which is untreatable.
Things that do not cause it
- Wearing glasses. This is the most persistent worry parents raise and it is completely unfounded. Glasses correct the light entering the eye and do not affect how it grows.
- Wearing a prescription that is slightly too strong. Under-correcting was once thought to help and the research went the other way.
- Reading in dim light. This is folklore.
- Sitting close to the television. Sitting close is usually a symptom of myopia rather than a cause of it.
What does influence it
- Genetics, which is the largest single factor. If one parent is nearsighted the risk roughly doubles, and with two it roughly triples.
- Age at onset. Earlier onset predicts a higher final prescription, simply because there are more growing years ahead.
- Time spent outdoors, which is one of the more consistent findings in the research. Roughly two hours a day is the figure most often cited, and the effect appears strongest for delaying onset.
- Sustained near work, which is associated with faster progression, though the relationship is less clean than the outdoor one.
What can actually be done
This is the part that has changed within my career. Twenty years ago the answer was a stronger prescription each year and a shrug. Now there are four approaches with real evidence behind them.
- Orthokeratology
- A rigid lens worn overnight that reshapes the cornea while your child sleeps. They see clearly all day with nothing on their eyes. It corrects the vision and slows progression at the same time, which is why it appeals to parents of children in sport.
- Low-dose atropine
- A single diluted drop at bedtime. No lens to handle, which makes it the easiest option for younger children and for families not ready for contact lenses. Used with ordinary glasses.
- Myopia-control soft lenses
- Daily disposables with an optical design that creates peripheral defocus, signalling the eye to slow its growth. Worn by day, thrown away at night.
- Myopia-control spectacle lenses
- Glasses with a treated peripheral zone producing a similar signal. No lens handling at all, and a sensible conservative starting point.
The window, and why it does not reopen
Myopia usually appears between six and twelve and progresses fastest in the years just after onset. Treatment works by influencing growth that has not happened yet, which means you cannot recover progression that has already occurred.
That is the single most important practical point in this article. A parent who starts treatment at eight has considerably more to work with than one who starts at thirteen. Both are worth doing. They are not equivalent.
If one or both parents are nearsighted, an early baseline exam is worth booking even with no complaints, because a child will not tell you their vision is changing. They have no basis for comparison.
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Read about myopia managementThis article is general educational information, not medical advice or a diagnosis, and it is not a substitute for an examination. If you are experiencing sudden vision loss, eye pain or an eye injury, contact us immediately or go to an emergency room.