Being short-sighted: definition, how a short-sighted person sees and how myopia progresses

Being short-sighted (myopia) means having an eye that is too long, or a cornea that is too steeply curved, which forms the image of distant objects in front of the retina: you see clearly up close and blurred in the distance. It is the most common vision defect: half of the world’s population could be short-sighted by 2050. Myopia most often appears in childhood and stabilises in young adulthood. Glasses, contact lenses and surgery correct it; in children, treatments can slow it down.

UNDERSTANDING

What is myopia?

In an eye with no refractive error, called emmetropic, the cornea and the crystalline lens bring light from distant objects to a focus exactly on the retina. In a short-sighted eye, this focal point falls in front of the retina: by the time the light reaches it, the rays have already crossed and spread out again, and the distant object looks blurred. Rays coming from close objects, which diverge more, are focused further back, on the retina: near vision is clear.

Most often, the eye is too long from front to back: this is axial myopia. Less often, the eye is of normal length but its optics are too powerful – a cornea that is too steeply curved, or a crystalline lens whose power increases, as at the start of a cataract: this is refractive myopia. In both cases, it is measured in negative dioptres, the sphere on your prescription (see the anatomy of the eye).

VISION

How does a short-sighted person see?

Clear up close, blurred in the distance – and the limit can be calculated: by optical definition, the furthest distance seen clearly without correction equals one metre divided by the myopia in dioptres.

A short-sighted person screws up their eyes to read a sign (the word “myopia” comes from the Greek for “one who squints”) and sees halos at night. With correction, they generally recover normal visual acuity; our vision simulator shows what they see depending on their correction. A child does not complain: they move closer to the television and struggle to copy from the board (see myopia in children).

THRESHOLDS

Low, moderate, high myopia: from how many dioptres?

These thresholds are conventions. The consensus of the International Myopia Institute (Flitcroft 2019) sets the onset of myopia at a spherical equivalent of −0.50 D and that of high myopia at −6.00 D; between the two, the meta-analysis by Haarman (2020) distinguishes low myopia, from −0.50 to −3.00 D, and moderate myopia, from −3.00 to −6.00 D. Some studies place high myopia from −5.00 D (Holden 2016) or add a “very high” category beyond −10 D (Matamoros 2015).

In France, the Matamoros series (2015), 100,429 people seen in refraction centres, found 39.1% to be short-sighted: 25.1% with low myopia, 10.6% moderate, 3.4% high, including 0.5% very high, with a possible recruitment bias acknowledged by the authors. Worldwide, the meta-analysis by Holden (2016) counted 22.9% of people with myopia in 2000 and projects 49.8% in 2050, with high myopia rising from 2.7% to 9.8%: this is described as an epidemic, associated with urbanisation and longer years of education, with a causal role demonstrated for education (Morgan 2021).

CAUSES

What causes myopia?

Heredity first: in the Australian Raine cohort (Lee 2022), each short-sighted parent increased the odds of becoming short-sighted between the ages of 20 and 28 by 57%. Many genes are involved, each playing a small part; heredity sets a predisposition, and the environment largely decides whether it is expressed.

Time spent outdoors is the most firmly established protective factor: the meta-analysis by Sherwin (2012) calculates that each additional hour outdoors per week reduces the odds of myopia in children by 2%, i.e. 13% for one additional hour per day, and randomised trials have confirmed this (Morgan 2021). The leading hypothesis is that daylight, far more intense than indoor light, may slow the elongation of the eye. Close work also plays a part, but a smaller one: the meta-analysis by Huang (2015) finds 14% higher odds of myopia in the children who spend the most time on it. For screens, Foreman (2021) reports a 26% higher risk, based on self-reported times, and Morgan (2021) considers this evidence “weak and inconsistent”. What matters is the overall pattern: hours of close work, indoors, at the expense of hours outdoors.

PROGRESSION

How does myopia change with age?

In everyday practice, myopia most often appears at primary-school age, progresses during growth, slows down in adolescence and generally stabilises at around 20 to 25 years of age. The earlier it starts, the more time it has to progress: this is what is at stake in myopia control.

Stability in adulthood is not absolute. In the Raine cohort (Lee 2022), between the ages of 20 and 28, 14% of those who were not short-sighted became so and 37.8% of participants saw their correction increase by at least 0.50 D, at an average rate of −0.04 D per year, much slower than in childhood. Myopia that changes markedly after the age of 30 should prompt a search for a cause: early cataract, poorly controlled diabetes, certain medicines. Refractive surgery, for its part, requires a stable correction – from the age of 18 if this is the case.

RISKS

High myopia: why the retina needs monitoring

A myopic eye is most often an eye that is too long, and the higher the myopia, the more its retina is stretched and thinned. The meta-analysis by Haarman (2020) quantifies what this costs compared with a non-myopic eye: the risk of retinal detachment is multiplied by about 3 in low myopia, 9 in moderate myopia and 13 in high myopia; the risk of myopic maculopathy, a deterioration of the centre of the retina, is multiplied by 14, 73 and 845; glaucoma and cataract are more common. The authors conclude that low and moderate myopia already carry “considerable risks”.

A short-sighted person, especially beyond −6 D, therefore benefits from a regular examination of the back of the eye, with the pupil dilated, to detect weak areas in the peripheral retina. A sudden shower of floaters, flashes of light or a dark curtain suggest a tear or a retinal detachment: you must see an ophthalmologist the same day or, failing that, go to the eye emergency department. Severe forms are described in the article on high myopia and pathological myopia.

CORRECTION

How is myopia corrected?

Correcting myopia means removing the excess optical power of the eye. Three methods achieve this.

• Glasses, with concave (diverging) lenses, remain the first-line solution.
• Contact lenses, soft or rigid, offer a full field of vision and a true-size image; at the Cachan practice, they are fitted by Dr Tourabaly’s associates. A red eye while wearing contact lenses means you must remove the lens and see an ophthalmologist the same day or, failing that, go to the eye emergency department.
• Refractive surgery, for adults whose correction is stable: LASIK, PRK and SMILE reshape the cornea with a laser, at the Clinique Laser Victor Hugo (Paris 16th); the ICL phakic implant, placed inside the eye at the Clinique Sainte-Geneviève (Paris 14th), is intended for high myopia or corneas too thin for laser treatment.

Indications, treatable ranges and results are detailed on the myopia surgery page. An operation corrects the optical defect; it does not shorten the eye: retinal monitoring for a person with high myopia remains the same after the procedure.

CHILDREN

Slowing myopia in children

Since the retinal risk increases with every dioptre, limiting progression during childhood has become a goal of care. Low-dose atropine eye drops are the most thoroughly evaluated treatment: in the LAMP trial (Yam 2019), in 438 children aged 4 to 12, myopia had progressed after one year by −0.27 D with 0.05% atropine, compared with −0.81 D with placebo, 0.05% being the most effective concentration, with no effect on visual acuity or quality of life. Dr Tourabaly prescribes atropine at 0.01% or 0.05%, and now gives preference to 0.05%.

Myopia control contact lenses and orthokeratology, fitted at the Cachan practice by Dr Tourabaly’s associates, and specific spectacle lenses complete the range of options, and time outdoors is still recommended. The options are compared in the article slowing myopia in children.

MYTHS

Two myths about myopia

“Myopia protects against presbyopia”

Half true. Presbyopia is the ageing of the crystalline lens, which loses its ability to focus up close; it affects everyone, short-sighted people included. But a person with −2 to −3 D of myopia keeps, without correction, a point of clear vision between 33 and 50 cm: with their glasses off, they read without effort. With their correction, they are presbyopic like everyone else, and a person with high myopia gains no advantage from it. An operation for myopia alone does not prevent presbyopia from setting in; dedicated techniques then exist, such as PresbyLASIK.

“Wearing glasses makes myopia worse”

False – studies even suggest the opposite. In a two-year trial in 94 children aged 9 to 14 (Chung 2002), those whose correction had been reduced by about 0.75 D saw their myopia progress faster; the 2020 Cochrane review (Walline) found 0.15 D more progression in undercorrected children, with a low level of evidence. Wearing your full correction remains the rule.

Dr Tourabaly sees patients for consultations at the Cachan and Paris 13 practices, and at the Cabinet ophtalmologique Sorbonne Saint-Michel (Paris 5th). Children are seen from the age of 3 at the Cachan practice.

Frequently asked questions

Consultations in Cachan, Paris 13 and at the Sorbonne Saint-Michel practice (Paris 5th) · Tel. +33 1 45 47 08 11

Scientific sources

• Holden BA, et al. Global prevalence of myopia and high myopia and temporal trends from 2000 through 2050. Ophthalmology. 2016. PMID 26875007
• Flitcroft DI, et al. IMI – Defining and classifying myopia: a proposed set of standards for clinical and epidemiologic studies. Invest Ophthalmol Vis Sci. 2019. PMID 30817826
• Haarman AEG, et al. The complications of myopia: a review and meta-analysis. Invest Ophthalmol Vis Sci. 2020. PMID 32347918
• Matamoros E, et al. Prevalence of myopia in France: a cross-sectional analysis. Medicine (Baltimore). 2015. PMID 26559276
• Sherwin JC, et al. The association between time spent outdoors and myopia in children and adolescents: a systematic review and meta-analysis. Ophthalmology. 2012. PMID 22809757
• Huang HM, et al. The association between near work activities and myopia in children: a systematic review and meta-analysis. PLoS One. 2015. PMID 26485393
• Morgan IG, et al. IMI risk factors for myopia. Invest Ophthalmol Vis Sci. 2021. PMID 33909035
• Foreman J, et al. Association between digital smart device use and myopia: a systematic review and meta-analysis. Lancet Digit Health. 2021. PMID 34625399
• Lee SS, et al. Incidence and progression of myopia in early adulthood. JAMA Ophthalmol. 2022. PMID 34989764
• Chung K, et al. Undercorrection of myopia enhances rather than inhibits myopia progression. Vision Res. 2002. PMID 12445849
• Walline JJ, et al. Interventions to slow progression of myopia in children. Cochrane Database Syst Rev. 2020. PMID 31930781
• Yam JC, et al. Low-Concentration Atropine for Myopia Progression (LAMP) Study: a randomized, double-blinded, placebo-controlled trial of 0.05%, 0.025%, and 0.01% atropine eye drops in myopia control. Ophthalmology. 2019. PMID 30514630

This article is intended for information purposes and does not replace a medical consultation. Indications, expected benefits and risks depend on each individual situation. For any question concerning your vision, consult an ophthalmologist.