Myopia — short-sightedness, explained

If your prescription starts with a minus sign, you are short-sighted. Distance is blurry, near is naturally sharp, and the number tells you how much lens power it takes to move the focus back onto your retina.

What is physically happening

In a myopic eye, light from far away comes to a focus slightly in front of the retina rather than on it. Usually the eyeball is a little too long front-to-back; sometimes the cornea is a little too steep. Either way, distant objects blur while close ones — whose light arrives at a steeper angle — still land correctly. That is why short-sighted people often read comfortably without glasses.

How the number reads

• Up to −3.00 D — mild. You navigate a room fine; you lose signs, faces across a street, a whiteboard.
• −3.00 to −6.00 D — moderate. Correction becomes the default rather than task-specific.
• Beyond −6.00 D — high myopia. Worth following closely: it carries a raised lifetime risk of retinal detachment, glaucoma and myopic maculopathy, independent of how well the glasses correct vision.

That last point is the one most people are never told. High myopia is not just a stronger prescription — it is a structurally longer eye, and length is what the risk tracks.

In children, it usually progresses

Childhood myopia typically starts between about 6 and 14 and increases while the eye is still growing, often stabilising in the late teens or early twenties. Because of that growth window, myopia management — specialised contact lenses, low-dose atropine, particular spectacle designs — aims to slow the rate, and every one of those decisions is made by comparing measurements over time. Axial length, where it is measured, matters even more than the prescription.

Does it ever go away?

Not on its own. It can appear to shift in later life: cataract formation can temporarily make an eye more myopic (occasionally restoring some near vision — "second sight"), and refractive surgery changes the prescription without changing the underlying eye length or its risks. Keeping the pre-surgery prescription on record matters for exactly that reason — a surgeon planning a cataract lens implant decades later will want the original numbers.