Myopia, the most common visual defect: what it is and how to treat it

By Cristiano Antonino On Jul 18, 2023

Refractive anomaly, myopia is the most widespread visual defect: in Europe it affects 30% of the population, with varying degrees of seriousness

Caused by a variety of factors, the incidence of myopia is steadily growing

In 2015, a WHO (World Health Organisation) report linked myopia to less and less time spent outdoors.

Today, children and young people devote a large part of their days to video games and mobile phone, tablet and computer screens: habits that can create visual disturbances.

This is confirmed by research by the American Academy of Ophthalmology, based on a meta-analysis of 145 studies on the increase in cases of myopia: by comparing the disease’s prevalence rates with data on urbanisation and demographic trends, the research predicted that, by 2050, half the world’s population could suffer from myopia.

The cause? Changing lifestyles and increasing education: in Europe, 50 per cent of university graduates between the ages of 45 and 49 are affected by myopia (compared to 26 per cent among high-school graduates).

The reason is to be found in the long hours spent on books or otherwise indoors.

Prevention plays a key role in reducing the likelihood of suffering from visual impairment over time.

Myopia: what is it?

Myopia is a refractive anomaly (or ametropia): in those who suffer from it, light rays coming from infinity are not focused correctly on the retina but in front of it.

This is because the refractive power of the ocular diopter is excessive in relation to the length of the bulb.

Its name, of Greek origin, means ‘squinting’, a term that refers to the gestures of those who suffer from myopia and try to see better what is in front of them (when squinted, the eyelids act as a natural diaphragm and increase the depth of focus).

In the eye of a healthy person, the light rays that pass through the dioptric means and enter the eyeball converge on the retina; in the eye of a myopic person, they converge in front of it.

The remote point (i.e. the furthest point from the eye where there is clear vision) is therefore not located at infinity but at a finite distance, unlike what happens in a healthy eye.

This is why myopes see well up close and poorly from a distance.

Myopia manifests itself in each subject at a different intensity.

And, the maximum distance at which the patient can see is inversely proportional to the degree of myopia.

Myopia: causes and types

The cause of myopia is mainly genetic.

Individuals with excessive eyeball length, or with an altered curvature of the refractive surfaces of the eye, develop the condition.

Much depends, however, on the type of myopia:

axial myopia is caused by a longer-than-normal eyeball length;
index myopia is caused by a higher-than-normal refractive index of the crystalline lens, despite the presence of a normal eyeball (a very common condition in cataract sufferers);
keratoconus myopia is caused by a cone-shaped cornea (the cornea thins and wears down to the appearance of a cone, increasing its curvature and causing myopia). Often the sufferer also suffers from astigmatism, and in severe cases a corneal transplant is required;
accommodative spasm myopia is caused by the front surface of the crystalline lens being more curved than normal;

In addition to being hereditary, the cause of myopia can be developmental.

Often the pathology develops due to excessive proximal work, many hours spent on books or in front of a screen.

This is why doctors and paediatricians recommend spending time in the open air every day.

Greater exposure to natural light in fact releases dopamine, a neuromodulator that inhibits elongation of the eye (and myopia is in many cases associated with a longer-than-average eye).

On the other hand, holding books, tablets, mobile phones and computers too close to the eyes leads to adjusting their focusing system to a closer distance, which is precisely what myopia is.

A research conducted by Sun Yat-Sen University in Guangzhou (China) involved more than 2000 primary school pupils: 952 underwent 40 minutes of daily physical activity, 951 maintained their usual lifestyle.

The study showed an absolute difference of 9.1% in the myopia incidence rate between the two groups, which represents a relative reduction of 23% after 3 years.

Myopia can therefore be

simple (the eye is too long for its optical power)
acquired or functional
developmental
congenital (already present at birth, or develops within the first 6 years)
pathological or degenerative (the eyeball undergoes excessive elongation, associated with developmental complications of the ocular fundus)
nocturnal (occurs only in low light conditions)
empty field (occurs in the absence of stimuli, e.g. in foggy conditions)
pseudomyopia (the subject experiences visual blurring caused by a spasm of the ciliary muscle, which may be temporary or permanent)

While sometimes more or less serious pathologies underlie myopia, other times the patient may suffer from a transient form of myopia caused by medication, hyperglycaemia or trauma to the eyeball.

Myopia: the symptoms

The primary symptom of myopia is difficulty seeing from a distance.

However, there are other symptoms that may appear more or less frequently:

burning eyes
visual fatigue
headaches
night blindness
reduced vision
narrowing of the visual field

Myopia: treatments

Depending on its severity, age and the patient’s health condition, myopia can be corrected in different ways.

These are the main corrective methods

spectacles with lenses that make the parallel rays diverge
soft or rigid contact lenses
refractive surgery

Refractive surgery using lasers, which has become increasingly popular in recent years, allows the corneal layers to be removed in order to change the refraction of the cornea.

The laser is an excimer laser: it therefore emits light at a very high pulsating frequency for a very short time.

Each time it passes over the cornea it removes one micron of thickness, and the number of passes depends on how severe the myopia is: a myopia of 3 dioptry requires the removal of 30 microns of cornea.

The cornea is ‘flattened’, so less light rays are refracted and fall onto the retina.

The first procedure to use the excimer laser to correct myopia and other refractive errors was photorefractive keratectomy (PRK).

Still used today, this procedure allows the curvature of the cornea to be surgically corrected by removing tiny fragments of tissue from the corneal stroma by ablation (vaporisation).

However, recovery of vision is not immediate (1-3 months), and it is possible to experience transient corneal opacities in the surgical area.

These usually resolve within six months.

Other side effects may include reduced visual acuity due to an irregularity of the corneal surface, pain, tearing, glare or foreign body sensation.

An alternative is LASIK, which can also successfully correct astigmatism and hypermetropia.

Unlike photorefractive keratectomy, the laser does not act directly on the surface of the cornea but in the corneal stroma (its intermediate portion), thanks to a previous incision made with the micro-keratoconus.

Visual recovery is very quick, as it occurs in a maximum of three days, but the procedure is not indicated for people with thin corneas or with particular corneal abnormalities.

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More recently introduced is the SMILE technique, which uses a femtosecond laser to create a corneal lenticule that is then extracted through a small incision without the use of an excimer laser.

It is reported to have similar effects to LASIK with excellent and faster post-operative results.

The different techniques make it possible to correct myopia up to more than 10 dioptry.

The operations are performed on an outpatient basis, anaesthetising the eye with a special eye drops.

To undergo such surgery, the subject must be over 20 years old and have had stable myopia for more than two years.

He must also not

suffer from diabetes
suffer from connective tissue diseases, from rheumatoid arthritis to Sjogren’s syndrome
having keloids
take the contraceptive pill, as retaining fluids increases the thickness of the cornea (and too much would be removed)
taking drugs that can cause corneal opacities

Myopia: can it be prevented?

Preventing myopia is possible, especially in children and adolescents.

Experts agree that spending time in the open air, in the sunlight and looking far away is a very healthy habit: being constantly indoors, even worse if in front of a screen, on the contrary promotes myopia.

However, it is possible for a very young child to suffer from it.

In such cases, the cause runs in the family: children with one or both myopic parents are more likely to develop the refractive defect than their peers.

In this case, negative lens glasses are used to focus images on the retina.

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