Content

Introduction

Myopia is a vision defect that causes blurred vision of distant objects, while near vision is sharp or, in any case, good.

It is caused by the focusing of light rays coming from distant objects not on the retina, as occurs in the normal eye, but in front of it, making distant vision blurred.

From a technical point of view, myopia belongs to the group of ametropias (refractive anomalies of the eye), together with astigmatism and farsightedness.

Myopia is the most common visual defect, in the Western world it affects about 30% of the population while in Asia it exceeds 80%; the divergent lens is used to assess its extent, which corrects the defective focus.

Myopia is measured in diopters and can be divided into three stages:

  • mild, up to 3 diopters
  • moderate, from 3 to 6 diopters
  • high, over 6 diopters

It generally occurs in school age and tends to increase in the developmental period until it stabilizes after 20-25 years of age. If there are no particular diseases that can interfere, after this age, as a rule, myopia increases slightly.

Symptoms

The most common symptoms (symptoms) caused by myopia are:

  • eyestrain
  • burning in the eyes
  • headache
  • difficulty in night vision
  • need to frown and squint, to see more clearly
  • blurred vision from afar
  • reduced vision

The intensity of these disorders can vary from person to person in relation to the degree of myopia.

Students often realize that they cannot see the blackboard well, that those who are driving cannot read the road signs in time, in front of the television or the cinema that they have a blurred vision of the images. So, the first part of the space that short-sighted people can't see well is what we can define as "far" but, if myopia is more important, "medium distance" vision can also be penalized (from 60 cm to 200 cm).

Myopia can be associated with other eye diseases including the appearance of cataracts (when the lens becomes opaque) and glaucoma (a disease characterized by an increase in eye pressure). In people with severe myopia, greater than 5-6 diopters, there is also an increased risk of detachment of the retina, the tissue of nervous origin that covers almost the entire inner wall of the eye.

Causes

The main causes of myopia include:

  • excessive length of the eyeball (axial myopia)
  • greater curvature of the cornea (the membrane that covers the front of the eye), referred to as keratoconus myopia, or of the crystalline (the natural lens that allows you to focus), referred to as accommodative spasm myopia
  • excessive refractive power of the lens, (abnormalities in the light trajectory referred to as index myopia)

The onset of myopia can be linked to both genetic and environmental factors related to lifestyle.

Although it is shown that those with myopic parents are more likely to develop myopia in the course of their lives, in recent years studies have shown how the individual's lifestyle and behavior are closely related to the onset of the disorder: children who spend a lot of time indoors, for example, doing activities up close such as reading in artificial light, computers or video games are more at risk. For this reason, in some countries, to counter the increasingly frequent occurrence of the phenomenon, schools are adopting programs that include activities in the open air and in natural light.

Myopia can also be of traumatic origin, caused by serious changes in the vascular membrane of the eye interposed between the retina and the sclerotic (choroid), the thin membrane that has the task of providing nourishment and oxygen to the various structures that make up the eye, or from contusions of the eyeball.

Then there is the transient myopia which can be caused by bruises, by taking certain drugs, by high blood sugar (hyperglycemia), by cataracts or by particular states of fatigue.

Diagnosis

The assessment (diagnosis) of myopia is carried out during the eye examination. The doctor measures the ability to focus and distinguish objects (visual acuity), through the reading of ten lines of letters, numbers and other characters of increasing size reduced sequences on a display board The measurement is evaluated in tenths which represent the lines that can be read without the help of corrective lenses diopters, instead, indicate the power of the lenses necessary for the clear vision of the symbols on the board.

The eye examination allows you to check the number of missing diopters; the specialist, during the visit, with the help of an eye drop that causes dilation of the pupil, and the temporary paralysis of the focusing function (accommodation), can analyze the fundus of the eye (ie the whole of the ocular structures located behind the iris and the lens) to determine whether myopia is simple or degenerative. Furthermore, through the schiascopy (technique to determine the refractive power of the eye, in practice for the measurement of sight) evaluates with great precision the severity of the refractive defect. In this technique the specialist uses an instrument, called schiascope, that emits a beam of light that is projected inside the eye; by observing where the light beam is focused, whether on the retina or in front or behind it, it is possible to determine whether it is a myopic or farsighted eye and evaluate the " transparency "of the eye. Today a so-called apparatus is also used for the evaluation and measurement of this refractive defect self-refractometer.

Therapy

While in the normal eye the path of light rays is modified by the transparent membrane located in the front part of the eye (cornea) and by the crystalline lens, a natural lens located inside the eye, in such a way as to make them converge on the retina, in the myopic eye the light rays converge in front of it causing a blurry vision of objects.

To correct this visual defect, several tools are available:

  • eyeglasses
  • contact lenses
  • surgery

Glasses and contact lenses are the most used means for the correction of myopia.In particular, for children and adolescents the use of glasses is preferable, above all because they are more manageable than contact lenses, both from the point of view of cleaning and for their maintenance. increased risk of sensitization to the lens material.

The choice of eyewear model is also important:

  • the upper edge of the frame must reach the eyebrow, so that the child does not see out of the lens when he looks up
  • the lenses must be unbreakable

It is not always possible to prescribe lenses so powerful as to totally eliminate the defect since not all people are able to adapt to them: it is possible to almost completely correct mild or moderate myopia, but not the highest degree. Adaptation usually decreases with increasing age.

If the defect is too high, glasses may not be the ideal means of correction. Since the perceived image is reduced and its sharpness is perfect only in the central part of the lens, while there are distortions in the area around the central and peripheral ones of the visual field, problems may arise such as an "incorrect assessment of distances and depth.

In the case of severe myopia one is forced to choose rather thick and heavy frames which can create various inconveniences; even if several advances have been made in this regard in recent years, there is still a long way to go.

Contact lenses allow a better visual quality than glasses, do not cause image shrinkage or peripheral distortion and solve various aesthetic and functional problems.However, they are not tolerated by all people and also have the drawback of being affected by certain atmospheric and environmental conditions (for example, wind, dust, pollen, etc.) which make their use more complicated.

It is important to maintain good maintenance of the lenses, which are certainly more delicate than glasses, to avoid even annoying problems such as infections, conjunctivitis, dry eyes and poor oxygenation of the cornea (corneal hypoxia). In some cases, wearing contact lenses can be difficult or take some getting used to.

As an alternative to the use of glasses and contact lenses it is possible to resort to various so-called surgical techniques refractive. With the introduction of the laser, many advances have been made for the treatment of various visual defects, allowing less invasive interventions and shorter recovery times. modifying the curvature of the cornea and, consequently, its refractive power, allowing the images to be focused.

For the correction of myopia the excimer laser, the techniques practiced are:

  • PRK (Photo Refractive Keratectomy)
  • LASEK (Laser Epithelium Keratomileusi)
  • LASIK (Laser in Situ Keratomileusi)
  • SMILE (Small Incision Lenticule Extraction)

There PRK is the most performed surgery for the correction of myopia in Europe. It consists in the use of a "cold" laser, which does not burn the tissues but vaporizes them (through a process called photoablation). The operation allows to remove a thin layer of superficial tissue of the cornea (epithelium) obtaining a flattening. Through the use of the laser it is possible to remodel the curvature of the cornea with extreme precision.

There LASEK, unlike PRK, it requires that the corneal epithelium is not removed but raised and repositioned after laser treatment.

There LASIK it involves the incision of the superficial layer of the cornea and the remodeling and smoothing with the laser of the central part of the cornea itself.

A variation of the LASIK technique is the iLASIK, also known as IntraLASIK or FemtoLASIK, in which, instead of the surgical blade, an ultra-fast and high-precision laser (femtosecond laser) is used to create a thinner flap of corneal tissue (corneal flap). Then we proceed to the treatment with the excimer laser to correct the visual defect and, finally, to the repositioning of the flap.

There SMILE (Small Incision Lenticule Extraction), is currently the most advanced technique. It allows, through the use of the femtosecond laser, to operate with excellent high myopia results, even in people with a thinner cornea. This technique is absolutely painless, safeguards the corneal structures as a whole and allows immediate visual recovery.

Finally, the implantation of intraocular lenses (IOL) allows a definitive correction of the visual defect. This technique is generally used when it is not possible to undergo other types of interventions. It consists of the "implantation of lenses inside the eye" very small eyeglasses capable of restoring the ability to focus. This type of surgery is reversible.

The techniques described are usually performed in an outpatient clinic, under local anesthesia and usually last no more than thirty minutes.

The best age to undergo refractive surgery is between 25 and 40 years, a period in which, generally, the vision defect stabilizes; after the age of 40, the risk of onset of difficulty seeing well up close (presbyopia) and other disorders, such as dry eyes, which can cause a feeling of discomfort after the operation, increases.

Prevention

According to the most recent studies, myopia can be prevented to a limited extent and it is very important, as soon as the defect appears, to use appropriate corrective lenses to slow down its evolution.

Adopting a correct lifestyle is certainly important, it has been shown, in fact, that children who spend a lot of time outdoors tend to develop myopia more difficult than those who spend many hours indoors and in artificial light. and teens also "unbalanced eating or a" high amount of hours spent in close-up reading or with electronic devices have also been associated with a higher likelihood of developing myopia.

It should not be forgotten, however, that the problem is also linked to genetic reasons: children of myopic parents are more likely to develop myopia in turn.

Complications

Myopia can be caused by an "imperfection in the structure of the cornea, lens or eyeball. When it is caused by a defect in the cornea or lens it is referred to as refractive myopia, when the defect is due to the excessive growth of the eyeball, it is referred to as axial myopia.

Refractive myopia usually occurs between 11 and 18 years of age and typically causes mild to moderate myopia. Axial myopia tends to occur at an early age, around the age of 6-7, and usually causes high or very high myopia.

The bulb of a normal eye has a length between 22 and 24 millimeters, in axial myopia there is an excessive elongation of the eyeball which, over time, can even reach 30 millimeters and cause different types of degeneration of the fundus of the eye. (in fact we speak of degenerative myopia).

Various complications can occur affecting the retina and the choroid, the thin, vascularized membrane, which is located in the middle layer of the eye. Due to the excessive elongation of the eyeball, the retina can present some thinning (peripheral retinal degeneration) which can cause small retinal tears through which the vitreous body can insinuate, causing the retina to detach from the ocular fundus.

Degenerative myopia can give rise to various eye diseases, such as it myopic staph: exhaustion of the eyeball affecting the posterior pole of the eye, associated with degenerative changes in the choroid and retina (eg chorio-retinal atrophy).

The most serious complication is represented by exudative myopic maculopathy, an extremely dangerous pathology for central vision, characterized by an excessive and abnormal production of new blood vessels (pathological neovascularization) at the level of the choroid and by the formation of a neovascular membrane, a structure that forms following the abnormal formation of blood vessels under the central portion of the retina. This process causes the lifting of the macula, a small central area of ​​the retina rich in photoreceptors and responsible for central vision in color and "high definition".

It is very important that people suffering from degenerative myopia undergo regular eye checks for constant and thorough monitoring of the fundus.

Living with

In everyday life, myopic people who do not use glasses or corrective lenses suffer from various discomforts: they do not have clear vision while driving, especially at dusk and during the night, they have difficulty reading road signs, the number of the bus in distance, the display with the timetables at the station or at the airport, find it hard to watch television, students have difficulty reading the blackboard. Moreover, especially in medium and strong myopia, they can experience the phenomenon of "flying flies" (floaters ): thickenings of the vitreous body that cast annoying moving shadows on the retina, causing the presence of filiform or point-like objects within the visual field. The problem, although annoying, is not serious, but an eye check is recommended to exclude the association with other diseases. Currently, there are no specific drugs or treatments for the problem of floaters.

In general, the discomfort caused by myopia can be minimized thanks to the use of corrective lenses or by resorting to refractive surgery. The discomfort that some people complain about also concern the social and relationship spheres: some, in fact, especially in the case of high myopia, try discomfort in wearing corrective glasses because the lenses can be very thick and create aesthetic problems.

Contact lenses solve the aesthetic problem but need more attention and care.

Bibliography

NHS. Short-sightedness (myopia) (English)

Mayoclinic. Nearsightedness (English)

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