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WHAT ARE REFRACTIVE ERRORS?
To get a clear view, light rays came through the structures of the eye and are focused onto the retina membrane that lines the inner cavity of the eye. The cornea is the transparent window of the eye, with the lens being located within it (the lens), are responsible for "refract" light rays, coming from outside, arriving to get perfectly focused to the retina, on the special area in the center called, the macula. The retina receives the image formed by light rays and sends it to the brain via the optic nerve, in the form of electrical stimulation.

Myopia (poor distance vision), hyperopia (poor near vision), and astigmatism (distorted vision), causing an influx of out of focus light to retina, usually by an imbalance in the optical structure of the eye, for example, a longer eye in myopics. Presbyopia (nearsightedness) occurs when the lens located inside the eye, the lens loses its ability to focus on nearby objects. These changes are called "refractive errors".

When the refractive error is due to mismatch of a single one of the optical structures of the eye are benign but when the defect is large, for example greater than 10 diopter myopia, usually associated other problems such as retinal pathology and In these cases we speak of malignant or pathological refractive errors. In early enough to fix the problem optical lenses with glasses or surgery, and in the second group, will also be necessary to correct the optical problem, it is necessary to strictly control the eye, as they may occur as cappings retinal alterations in the required laser treatment to seal and prevent a possible retinal detachment.

The most common symptoms of refractive errors are blurred vision and discomfort or eyestrain. All are fully correctable with glasses or contact lenses suitable or now by surgery.


MYOPIA (POOR DISTANCE VISION)
Myopia is the term used for the condition in which the eyes can see nearby objects cleanly but can not identify distant objects clearly. The word "myopia" comes from a Greek word meaning "closed eyes" because people with this condition often close eyes slightly to improve distance vision (pinhole effect).

Usually, myopia is a hereditary factor that is often evident in children around eight to ten years old. Normally, tends to increase as body growth during adolescence and into adulthood stabilized. Heredity or family history are the most influential factors in myopia. Other factors that could influence its development, reading or near vision tasks in low light conditions, or nutritional deficiencies, may be some of them.

Myopia can be caused by a greater length of the eyeball. The eye describes a more oval shape than round, and because of this increased length, it is impossible to modify the crystalline form sufficiently achieve sharp focus for distant objects on the retina. Less often, myopia may be caused by a change in the curvature of the cornea or a change in the crystalline form.

Patients diagnosed with a simple myopia, means that myopia may increase as the human body develops.

Although the increase of myopia should be the result of normal changes during growth. just as a child's body grows during adolescence, there are many changes in the length of the eye that cause the need for frequent changes in glasses or graduation, as you change shoes because the foot has grown. Nearsightedness can progress rapidly for a few years but after the changes are small. Between 20 and 40 years of age, these changes are minimal and may increase again to 60, coinciding with the start of a cataract.


TREATMENT:
The most popular option for treatment are glasses or contact lenses. In both cases there will be no curing the disease, but may reset focus light on the retina. There is no scientific evidence that tells us that contact lenses or eye exercises can stop the progression of myopia. Although some people use a process of adaptation of rigid contact lenses called orthokeratology, producing a temporary visual improvement. After termination of the use of contact lenses, the cornea returns to its original shape and curvature, or myopia appears again.

Medical treatment of myopia through the use of drugs has long been one of the most studied researches, but the reality is that there is no fully effective in this field.

Surgical treatment of myopia becomes more important and their study and research continue to advance. Thus, using different techniques "refractive surgery" can correct nearsightedness. Currently the most popular called LASIK, which by excimer laser is molded and corrects the corneal curvature by modifying the refractive power of the eye and, thereby, again focusing on the retina the light sporadically. This technique has shown good results, with great effectiveness, but is not without risks, especially those associated with the maneuver of the microkeratome corneal cut. Other alternatives are intraocular lenses, especially for high myopia or in cases of very thin cornea, can not be applied where the laser.

Myopia is often detected in school visual screening or routine checks on a visit to the optometrist or eye. Patients with myopia should conduct frequent reviews, especially in the growing years.


MALIGNANT MYOPIA
Malignant or pathological myopia is a less common form of myopia. Generally myopia is above 8 or 10 diopters, which is no longer a simple disorder or imbalance in the optical media of the eye. We can say that is a real disease, and the need to correct the optical blur, a number of alterations in the tissues of the eye, basically premature aging, where the retina is damaged structure. It has a more hereditary familial incidence. His progression is rapid and can be associated with macular hemorrhage or retinal detachment. Due to these circumstances is particularly frequent revisions necessary to prevent the degenerative process. When it detects a retinal disorder such as peripheral holes, laser may be applied to seal and prevent retinal detachment.


HYPEROPIA (POOR NEAR VISION)
Hyperopia is the term used to define a relatively good distance vision and near vision difficulty. In this condition, generally, the eye is shorter than normal (as opposed to myopia, where the eye is often longer). This decrease in the length of the eye causes a difficulty for the lens to focus on near objects on the retina with sharpness. To a lesser extent, a flattening or thinning of the cornea, can be also causes hyperopia.

Normally, all infant age children are farsighted moderate extent, and its value decreases during adolescence, when the eye develops, like the rest of the body's structures. Young people affected by this condition can usually see properly both in the far distance and in close, since the focusing power of the lens at these ages is powerful enough to offset the imbalance Optical.

Some hyperopia in children may be associated with a convergent strabismus, inward deviation of the eye, because the eye muscles contract strongly, pulling inward to make the extra effort that is the right approach.

Children usually have no visual symptoms such as headache or other visual fatigue, however, the loss of interest in reading can be an early warning of the existence of a certain degree of hyperopia requiring ophthalmologist visit prescription glasses for correction. Recall that this condition, like myopia, also has a hereditary basis with greater familial incidence, and when parents suffer farsightedness, is necessary from age 3 routine scans are performed each year by the ophthalmologist, for rule out its presence and, if you treat it as necessary, to prevent amblyopia (lazy eye) or strabismus convergent.


TREATMENT:
Farsightedness usually corrected with glasses or contact lenses and, by modern laser surgery. The correction of hyperopia in small children, especially when no additional visual symptom is not necessary. In these cases it is recommended that regular monitoring review by the ophthalmologist. Only in cases of high hyperopia or associated with ocular deviation need to be treated with glasses, contact lenses or surgery.


ASTIGMATISM
Astigmatism usually be caused by the irregularity or distortion of the cornea, anterior surface of the eye. In the case of a normal vision without distortion, the cornea tends to be uniform and of similar curvature in all directions, would be a nearly spherical surface. When an individual suffers from astigmatism, the cornea is deformed and is more curved in one axis, and if we take a round ball and compress it turns into an oval, is more like a football or a melon football. The effect of astigmatism in the perception of the figures is similar to that seen when looking at a mirror with a corrugated surface, such as those found at amusement parks that make us see much higher or wider or too thin. It is usually hereditary and is present at birth and often do not suffer large variations throughout life.

Most of the population has some degree of astigmatism and often do not require correction with glasses or contact lenses, is what we call physiological astigmatism.


TREATMENT
Astigmatism correction is not difficult if the distortion deformation is from a regular and defined in the cornea. In these cases, using a similar compensatory deformation glasses can neutralize the distortion of the cornea, just as we do with lenses or by surgery, where the laser molded to regularize the corneal surface, transforming it into spherical. In other situations like a scar resulting from trauma or surgical intervention may cause the deformation of the cornea is irregular. The so-called irregular astigmatism are hard to correct since it is not possible to make a glass or lens to compensate this deformation. If the injury is severe only can improve recomposing the cornea with a corneal transplant. Currently available laser systems that allow some degree of irregularities remodel and although it does not solve all cases, many of them can be solved without resorting to a corneal transplant, with the disadvantages that entails.

Normally, the blur due to astigmatism is corrected by glasses or contact lenses. Contact lenses or rigid gas permeable correct astigmatism better than soft contact lens, but there are also soft lenses that can resolve and often very helpful. If the amount of astigmatism is high, the crystals that correct this condition can cause distortion in the side. High powers are not easily correctable astigmatism with contact lenses, since the lens can be tilted on the corneal surface. Currently available lenses called toric lenses, which can solve the problem better. Are stable due to a change in its posterior curvature that conforms to the anterior surface of the cornea, improving stability. Subject of the anterior lens optic incorporate the modification corrects astigmatism.


PRESBYOPIA
As people get older experience greater difficulty focusing on close objects, necessitating the glasses for reading or near vision tasks. This condition is sometimes known as presbyopia.

Many people do not have near vision problems until after age 40, when the lens loses some of its flexibility and can not focus clearly on near objects. Presbyopia is an alteration inevitable, physiological, and usually corrected with glasses or contact lenses or, more recently, laser surgery or intraocular lens implants. Once you start will be increased gradually to 60 or 70 years. Generally graduation should be adjusted every 3 or 4 years, especially when it appears. Bifocals, trifocals or progressive rates may be the solution for suffering another presbyopic refractive error such as nearsightedness, farsightedness or astigmatism.

It has now been shown that certain eating habits can influence the course yn onset of presbyopia. Special exercises, visual therapies that have shown a significant improvement in the control of presbyopia, in delaying the onset and time to slow its progression.

 
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