What are refractive errors?

Many are the people who ask us about the difference between myopia and astigmatism, but for this it is also necessary to understand what hyperopia is and the differences between these three refractive errors. To achieve clear vision, light rays pass through the structures of the eye until you focus on the retina.

La cornea is the transparent window of the eye, along with the crystalline, which is the lens inside the eye, are responsible for deflecting or "refracting" the light rays that reach them from the outside, to achieve a proper focus. The retina receives light rays, transforms them into an electrical impulse and sends them to the brain through the optic nerve, and the optical path, so that it is elaborated and the visual image is constituted.

When the light does not reach the retina in a timely manner, the image that is generated is blurred. If light rays converge in front of the retina, myopia, if the convergence occurs behind, the farsightedness and when it is not a converging point but two or more foci coexist, the astigmatism.

myopia hyperopia astigmatism

La myopia (bad vision from afar), the farsightedness (poor near vision), and the astigmatism (distorted vision), are basically due to differences in the length or shape of the eye. The Presbyopia (tired eyesight) It happens when the lens inside the eye, the crystalline, loses its ability to focus on nearby objects.

Myopia, hyperopia, astigmatism and presbyopia constitute what is known as refraction disorders or ametropia.

When the ametropias are not exclusively an optical imbalance, but other problems are associated, they are considered a real disease and we call them myopia or hyperopia magna or pathological. In these cases, the prescription is usually high, greater than 8 or 10 diopters, and vision often does not reach its maximum potential, unity, even with adequate optical correction.

When ametropics are not exclusively an optical imbalance, but other problems are associated, they are considered a true disease and we call them myopia or hypermetropia magna or pathology. In these cases, the graduation is usually high, higher than 8 or 10 diopters, and it is common that the vision does not reach its maximum potential, the unit, even with the appropriate optical correction.The most common symptoms of refractive errors (excluding the magnificent forms), are blurred vision and discomfort or visual fatigue. All of them are fully correctable with glasses or contact lenses adequate or, currently, by refractive surgery.

Myopia

myopia

Myopia (poor farsightedness) is the term used for that visual situation in which close objects can be seen clearly, but distant objects cannot be correctly identified. The word “myopia” comes from a Greek term that means “closed eyes”, because people who suffer from it often close their eyes slightly, “squint” them by contracting the muscles of the eyelids (pinhole effect), forcing a better focus.

Usually, myopia has a hereditary factor, which explains the higher family incidence. Except in the magna forms, it usually becomes evident in children around four to ten years of age. The course of myopia is towards the increase of its values, that is, progressive vision loss during adolescence.

Normally, it usually increases in parallel with the growth of the body, during adolescence and tends to stabilize in adulthood, from the 20-21 years. Heredity or family history are the most influential factors in myopia. There are other factors that could influence your development, reading or near vision tasks, especially in low light conditions. Deficiencies in nutrition can influence its evolution, although there are no conclusive studies on this point.

Myopia is usually caused by a greater length of the eyeball. The eye grows excessively and takes on an oval shape. Due to this increase in axial length, it is impossible for the optical system of the eye, the sharp focus on the retina of distant objects. Less commonly, nearsightedness can be caused by a change in the curvature of the cornea or a change in the shape of the lens.

Treatment for myopia

The most used option for myopia treatment are glasses or contact lenses. In both cases, the disease will not be cured, but the correct focus of light on the retina can be restored. There is no clear scientific evidence to tell us that contact lenses or visual exercises can stop the progression of myopia, although studies have appeared that show an improvement, both in its evolution and in the visual quality achieved.

In recent years, various methods have appeared to treat myopia definitively. Some of them like:

Orthokeratology or Biofeedback

These are methods that need to be contrasted, since it has been observed that the initial improvement is partially lost when the therapy is stopped. In addition, we consider that they are not recommended for all myopes because undesirable side effects have been described.

Orthokeratology

La orthokeratology It is a technique used to correct ametropia: myopia, hyperopia and astigmatism. It consists of placing a lens that "molds" the cornea. Contact lenses for this purpose have parameters that shape the cornea, modify its curvature and the thickness of the epithelium. The problem is that it is necessary to put them on every night, since if it is not done, the cornea recovers its initial shape because it is a very elastic tissue, losing all its effect.

The other problem is that we "force" the cornea to a deformation, a stress, which is not always good and can remain as a negative residual factor, tolerance problems to contact lenses or the materials that constitute them. This practice had some boom among optometrists, but is almost in disuse and ophthalmologists usually do not recommend it for its poor effectiveness in relation to the problems caused, however, in recent years have appeared lenses with new materials and geometries that can seem provide benefits to certain patients, so we recommend those who have an interest in this topic, consult your ophthalmologist.

Biofeedback

It is a common practice of optometrists and consists of exercises to try to correct ametropia, basically myopia, without surgery. Accommodation is forced to achieve with it, that the light from the outside is focused on the retina, just like when we put on glasses, contact lenses or after surgery. The problem is that this type of exercise can cause disorders such as increased blood pressure and visual fatigue. On the other hand, the result is very debatable and is lost when you stop the exercises, so we do not recommend it as a fully effective therapy.

The medical treatment of myopia

Through the use of drugs, it has long been the subject of research, but reality shows that there is nothing fully conclusive in this campeither. Despite this, we know that a balanced diet rich in vitamins, especially A and E, are essential so that there is no progression greater than that which is genetically conditioned.

The surgical treatment of myopia

It is acquiring greater importance and its study and research continue to advance. There are various surgical alternatives to correct myopia. Currently the most popular technique for myopia operation It is called LASIK, in which an Excimmer laser molds and corrects the corneal curvature, modifying the refractive power of the eye and, with this, the light is once again focused on the retina in a timely manner. This technique has shown good results, with great effectiveness, although tampLittle is risk-free, especially those related to the corneal “carving” maneuver with the microkeratome. There are also other surgical alternatives, such as the implant of Phakic lenses or intrastromal implants.

Pathological myopia

Pathological myopia is a less frequent form of myopia. Generally they are called those myopias superior to 8 or 10 diopters, in which it is no longer a simple disorder or imbalance in the optical means of the eye, which can be corrected through glasses or contact lenses, but we are facing a series of alterations in the tissues of the eye in which the retina is the most damaged structure. It has a hereditary character and its incidence is usually familiar.

Its progression is rapid, and may be associated with complications such as macular hemorrhages or retinal detachment. Due to these circumstances, it is especially necessary for people who suffer from it to carry out frequent check-ups to prevent the degenerative process and the problems that usually accompany the optical deficit.

When a retinal alteration is detected, such as peripheral holes, a thermal laser can be applied to seal them and thus prevent retinal detachment. In the cases of maculopathy secondary, when exudative membranes appear, new photodynamic treatments, vascular proliferation inhibitors or anti-angiogenic drugs can be applied.

In this type of myopia, the benefits of diet are also discussed and, although there are no conclusive studies, it seems that the contribution of vitamins and other types of antioxidants, anthocyanosides and gincobiloba extracts, could have a significant role in the prevention of complications , as well as an improvement in visual quality.

Farsightedness

Hyperopia (poor near vision) is the term used to define a process with a distance vision that may be relatively good, but with poor near vision. The cause of this imbalance is usually an eye of less than normal size, a short eye, contrary to what happens in myopia, in which the eye is usually longer. This decrease in the length of the eye means that the optical system of the hyperopic person does not focus clearly on the retina near objects. To a lesser extent, flattening or thinning of the cornea can also be causes of hyperopia.

It is common for us to confuse hyperopia with myopia. The difference between hyperopia and myopia is that the light rays that enter the eye, in the case of hyperopia are projected behind the retina, while in myopia they are projected in front of it. This fact causes blurred vision at short distance and long distance respectively.

farsightedness

Normally, all infants are hyperopic to a moderate degree, and this hyperopia decreases in value during adolescence, coinciding with the development of the rest of the body's structures.

Young people affected by this condition can usually see correctly both in the far distance and in the near distance; since the focusing power of the lens at these ages is powerful enough to compensate for the optical imbalance.

Some hyperopia in children may be associated with a convergent strabismus (deviation into the eyes), due to the fact that the ocular muscles contract strongly, pulling inwards, when making the over-exertion that the correct focus (accommodation) supposes. Children do not usually present visual symptoms such as headache or other types of eyestrain; however, in the face of loss of interest in reading or a delay in school performance, one must think about the possibility of poor vision that causes fatigue or reluctance and this may be a first warning of the existence of a certain degree of farsightedness that requires the visit of the ophthalmologist and the prescription of glasses for its correction.

It must be remembered that this condition, like myopia, also has a hereditary basis with a higher family incidence; Therefore, when parents suffer from hyperopia, it is necessary for children, from the age of 3, to go to the ophthalmologist for routine annual examinations to rule out its presence or treat it if necessary, in order to prevent the amblyopia (lazy eye) or squint convergent that may be a consequence of hyperopia (see review schedule).

Treatment of hyperopia

Farsightedness is usually corrected by glasses or contact lenses and, in modern times, by laser surgery for farsightedness. The correction of small hyperopia in children is not usually necessary, especially when they do not present other visual symptoms. In these cases, it is recommended to carry out regular check-ups with the ophthalmologist. Only in those cases of high hyperopia or associated with other symptoms or with ocular deviation, will they need to be treated with glasses, contact lenses or refractive surgery.

Also in hyperopia, the role of drugs and diet is discussed. There is no evidence of its benefit, but the studies carried out seem to indicate that a balanced diet and a significant supply of vitamins and other antioxidants can help in its evolution.

Astigmatism

astigmatism

Astigmatism (distorted vision) is usually consequence of a distortion or irregularity of the cornea and / or lens. When vision is normal, the cornea is usually regular with a similar curvature in all its axes. It is, then, an almost spherical surface.

When an individual suffers from astigmatism, the cornea is deformed and is more curved in one of its axes: it happens the same as when we take a round ball and compress it, which we see that it becomes oval and looks more like a rugby ball or a melon The effect of astigmatism on the perception of the figures is similar to what we see when we look at a mirror with a wavy surface, like those we find in amusement parks, which make us look much taller or wider or very thin (I suppose that many would not mind too much).

Astigmatism is also hereditary. It usually appears at birth and frequently does not undergo great variations throughout life. The majority of the population has some degree of astigmatism and often does not require correction with glasses or contact lenses. This is what we call physiological astigmatism. However, when the degree of astigmatism is greater than 1 diopter, causes distortion of the images we perceive, which implies that we make an over-effort to make them "useful", so that the brain can process them. This phenomenon supposes a greater tiredness, appearing symptoms of visual fatigue, headaches and loss of the habit of reading.

Treatment of Astigmatism

Astigmatism correction is not difficult if the distortion comes from a regular and defined deformation in the cornea. In these cases, through a compensatory deformation in the corrective lenses of the glasses, the distortion of the cornea can be neutralized and, in the same way, it will be possible to do it with contact lenses or with surgery. By means of the laser astigmatism surgery, we mold the cornea until the surface is regularized, transforming it back into a sphere.

In other situations, such as a scar from trauma, infection, or surgery, irregularities may appear on the surface of the cornea that can cause irregular astigmatism. Irregular astigmatisms are more difficult to correct since it is not possible to make a glass or contact lens that compensates for this deformation. If the injury is very severe, it can only be improved by recomposing the cornea through laser surgery, if the injury is located in the anterior layers of the cornea, or with a cornea transplant if the lesion occupies the deep planes.

Currently, we have laser systems with very sophisticated programs that allow us to reshape a certain degree of irregularities and, although not all cases are resolved, many of them can be solved without resorting to a corneal transplant, due to the inconveniences that this surgery supposes.

Rigid or gas permeable (RPG) contact lenses correct astigmatism better than soft contact lenses, although these have experienced a very important advance in recent years with the appearance of toric contact lenses. Astigmatism surgery has recently been incorporated into the therapeutic arsenal for this disease. Using the excimmer laser we can treat astigmatisms up to 5 or 6 diopters, and when the values ​​are higher we can resort to toric phakic intraocular lenses. As in other ametropias, it must be remembered that although these surgical methods offer very good results, they are not exempt from complications, which is why a prior study will be necessary to assess the chances of success and risks in each case.

3D video of the myopia, hyperopia and astigmatism operation


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    Summary
    Myopia, hyperopia and astigmatism
    Article name
    Myopia, hyperopia and astigmatism
    Description
    In this article we explain what myopia, hyperopia and astigmatism are, the reviews, what measures to adopt and the indications in the treatment.
    Author
    Name of the editor
    Área Oftalmológica Avanzada
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