Myopia (short-sightedness) is a refractive error: the eye sees clearly up close but blurry in the distance. It is the most common vision problem in the world, and it is becoming more frequent. This five-step guide explains simply what happens inside the eye, why myopia appears, how it is diagnosed, how it progresses and what the treatment options are.
Orange dot: where light rays meet. Orange line: the retina.
Key points
- Myopia blurs distance vision; near vision usually remains good.
- It most often comes from an eye that is slightly too long, more rarely from a cornea that is too curved.
- It is measured in negative dioptres: -1, -3, -6…
- Glasses and contact lenses compensate for it; refractive surgery can correct it in adults with stable vision, after a full assessment.
What happens inside the eye
To see clearly, the cornea and the lens must focus light rays exactly on the retina, the light-sensitive layer at the back of the eye. In a myopic eye, these rays meet in front of the retina: the image reaching the retina is blurred.
In most cases the cause is anatomical: the eye is slightly longer than normal (axial myopia). One extra millimetre of length corresponds to about three dioptres of myopia. More rarely, the cornea is too steep.
Degrees of myopia
Myopia is expressed in dioptres (D), with a minus sign on the prescription. It is usually classified as:
- low myopia: up to -3 D;
- moderate myopia: -3 to -6 D;
- high myopia: beyond -6 D (some international classifications use -5 D).
It is often associated with astigmatism, and from around age 45 with presbyopia.
Good to know
Short-sighted people often see better up close without their glasses: this is normal, and it is why many myopes over 45 take off their glasses to read.
A very common condition
About one person in three is estimated to be short-sighted worldwide, and projections published in the journal Ophthalmology suggest almost one in two by 2050. This rapid increase, too fast to be purely genetic, is largely explained by lifestyle: more time spent on near tasks and less time outdoors.
How can it be corrected?
Glasses and contact lenses compensate for myopia without changing it. Refractive surgery reshapes the cornea (LASIK, PRK, SMILE) or adds a lens inside the eye (implant). It is intended for adults whose myopia is stable and whose eyes are healthy, after a full assessment. The options are described in step 5 of the guide.
Further reading
Frequently asked questions
It is first of all an optical error, corrected with glasses, contact lenses or surgery. High myopia, however, calls for regular examination of the retina, because it carries a higher risk of certain retinal complications.
No treatment shortens a myopic eye. Glasses and lenses compensate for it; refractive surgery corrects the refraction durably in most cases, but does not change the length of the eye.
Prolonged near work, on screens or paper, and too little time outdoors are associated with a higher risk of myopia in children. The specific causal role of screens is still debated.
A short-sighted eye sees the distance blurred because the image forms in front of the retina. A long-sighted (hyperopic) eye has to make an effort to see, especially up close, because the image forms behind the retina.
This general information does not replace a consultation: only an eye examination can establish a diagnosis and discuss a suitable treatment.