Color blindness - is a general term for the inability to distinguish any color. This disorder can cause learning difficulties, become a problem when traveling on the roads, and even the limited career opportunities. For example, the ability to distinguish colors is necessary for those who are engaged in business printing or color photography. In some countries, people with various forms of color blindness at the legislative level is forbidden to perform certain types of work.

Causes of color blindness

Color vision depends on light absorption by visual pigments that are contained in special cells of the eye - the photoreceptors. There are two types of photoreceptors - rods and cones. Sticks provide the ability to see in dim light and do not have the ability to distinguish colors. The cones respond to color vision; they contain three types of pigment. Under normal color vision brain compares the electric signals from different types of cones.

Color blindness can be congenital or acquired. Congenital color vision is usually due to the fact that there are no visual pigments are missing, or they are functioning properly. Acquired color blindness may be the result of aging, or taking any medication. In such cases, except cones and visual pigments, and other damaged parts of the eye.

Kinds

There are three types of congenital color blindness groups: monohromatizm, dihromiya and anomalies in three colors. The last two groups are divided into disorders that are characterized by a lack of sensation in the red-green and blue and yellow regions of the spectrum. Lack of sensation in the red-green region of the spectrum is more common in men than in women. Impaired ability to distinguish between the colors blue and yellow part of the spectrum is rarely observed in both sexes.

• Monohromatizm or achromatopsia. People with such a distinguished feature of a different degree of brightness, but do not see colors. Their world looks like a black and white image. For people with this disorder also characterized by poor visual activity, poor tolerance to bright light, and nystagmus - rapid involuntary eye movements. To monohromatizm inherited, a person must obtain a gene of this disorder from both parents. This is a rare form of color blindness.
• Protanopia - a kind dihromii, which is characterized by impaired ability to distinguish between red and green colors. Often, people with this disorder, however, may be correct to call these colors, as green for them looks brighter than red. Men Protanopes sick, if they get the defective gene from their mother. In the future, they pass the gene to their daughters, but no sons. Women who received only one defective gene are carriers of protanopia; sick, only those who receive these genes from both parents. This is the most common type of color blindness.
• Tritanopia - a violation of the perception of colors yellow and blue part of the spectrum. As a rule, it causes less difficulty in carrying out daily duties than Protanopia.

Anomalies in three colors - less severe disorders associated with impaired ability to distinguish individual colors. People with the most benign forms of such disorders may not even be aware that they have violated color vision.

Cure congenital form of color blindness is not possible. Acquired disorders of color vision can sometimes be cured - usually with successful treatment of the underlying disease.

For people with color blindness are different contact lenses Contact lenses - whether they can completely replace the glasses?   and glasses that can correct some vision. However, because they can not provide a normal color vision, they must be used with caution.

What happens in the body in breach of color vision

It is known that catches the eye and refracts the rays emanating from objects. Refracted rays fall on the rear wall of the inner lining of the eye - the retina, which is a set of perceived information receptors - the rods and cones, which in turn transmit information to the optic nerve, where it goes to the brain.

For color vision cone cells are responsible, they are of three types: with a special pigment, perceiving red, blue or green. People who have all three pigment and perceives the three colors are called trichromats.

The study of color vision

As the number of occupations require maintain normal color vision (those associated with driving a vehicle, the military, and so on), before the employment of their color vision checked. For this purpose, two groups of methods used - pigment and spectral.

By pigmentary research methods include using colored (pigmented) tables and various test objects (sets of colored skeins of wool, the pieces of cardboard, and so forth). The most widely Rabkin polychromatic table. The main group of tables designed for the diagnosis of forms and degrees of congenital color vision disorders and their differences from the acquisition; a control group of tables - to clarify the diagnosis in difficult cases. These tables include the background of the same color circles are circles of different colors, but the same brightness that make up any number or shape, easily distinguishable normally sighted people, but invisible for various violations of color vision.

More subtle methods of diagnosis are spectral studies using a special device - anomaloscope. The method consists in the equation of two-tone color test fields, one of which is illuminated in yellow, and the other - the red and green and can change color from pure red to pure green. The test is to equalize the color, making the two colors of the second color field in yellow. This method can not only detect color blindness, but also to determine the sharpness of the color separately for each of the colors.

Color vision is of great importance in today's world, color blind must be aware of his defect, to avoid an unpleasant (and sometimes dangerous) situation.

  Galina Romanenko

Hyperopia - a kind of visual impairment, which is quite common in both children and adults. According to some estimates, many countries suffer from hyperopia up to 20-25% of the population. For example, in the course of large-scale survey among residents of Australia, 22.4% people said that they have more or less severe hyperopia. However, in statistics there can not be relied: the actual number of people with this disorder may differ significantly from the number of people who go to the doctor with complaints that they have difficulty seeing close objects, as well as the number of those who believe that their farsightedness.

The impact is far-sightedness has on human life, depends largely on its degree and the age and patient. So, far-sightedness in adults usually causes a certain discomfort and difficulty in performing certain types of work; children she, if left untreated, can cause complications such as strabismus and amblyopia, as well as a variety of problems with training.

Causes

The image perceived by a person focuses on the two parts of the eye - the cornea and lens. They refract incoming light so as to be directed to the retina clearly focused image. If the rays are refracted properly, there is an error of refraction. Hyperopia - one of the possible refractive errors. Instead of just focusing on the cornea focuses light behind it, because of which near objects are hazy.

Classification of farsightedness and static data

Refractive error - this is the ratio between the optical components of the eye (such as corneal curvature, refractive index of the cornea, the distance between the cornea, lens, vitreous body, and so on), and the axial length of the eye. Hyperopia - a refractive error is the fact that the parallel rays of light entering the eye focuses behind the retina instead of on it. This disturbance is divided into degrees, depending on whether the optical power (measured in diopters) required to light (which in the brain is transformed into visual images) focused on the retina. In addition, far-sightedness can be classified on the basis of what has led to its development as well as some other factors.

There are three main degrees of hyperopia:

• Low or weak sightedness - to two diopters (diopter);
• Moderate farsightedness - from 2.25 to 5 diopters;
• A high or severe hyperopia - 5 diopters.

There are also the following types of hyperopia:

• Simple hyperopia - the most common variety, is not associated with any abnormalities in the structure of the eye. Usually develops gradually, often mild or moderate;
• Pathological hyperopia caused by abnormalities in the anatomy of the eye, which are associated with developmental disorders, illness or injury;
• Functional farsightedness is a consequence of paralysis of ciliary muscle, resulting in a lens of the eye loses its ability to accommodation, that is, the change in refractive power, depending on how far away from the person is a subject which he treats.

Finally, we can distinguish congenital and acquired hyperopia.

Speaking of congenital hyperopia, it should be noted that most infants born at term and with normal weight, there is a mild form of farsightedness (about 2 D). However, only in rare cases they can be moderate or severe hyperopia (3.5 diopters) - that it is, as a rule, is the result of abnormalities in the development and that it is meant by the term "inborn farsightedness." Interestingly, in premature infants and / or children with low birth weight is more common or very weak hyperopia (about 0.24 diopters), or mild forms of myopia.

With age, the vision in the majority of children with mild farsightedness bounces back. With regard to moderate farsightedness, the proportion of children with visual impairment it also decreases with age among children aged 6 to 9 months it is 4-9% among children aged one year - 3.6%. Among the five-year olds refractive errors are even more rare, but there is still dominated by light farsightedness. In the age group 15 to 20 years, the proportion of adolescents and young people with farsightedness becomes even smaller, but it starts growing number of people with myopia.

Quite often, people diagnosed both hyperopia and astigmatism Astigmatism - lenses, glasses or surgery? . In astigmatism, visual acuity reduced, due to defects in the structure of a particular structure of the eye. There are mixed, distant and near astigmatism. With astigmatism, farsightedness person sees well removed from his subjects. For a person with mixed astigmatism Mixed astigmatism - a violation of   objects of virtually any distance are blurred - it can be said that he had nearsightedness and farsightedness at the same time, although this is not quite true. Astigmatism can cause a significant loss of vision and strabismus Strabismus - how to find the cause? So it's important to be identified and began to be treated as soon as possible.

Complications

Complications of farsightedness may include:

• Strabismus. Some children with hyperopia develop strabismus. Usually, to prevent occurrence of this problem or one can cope with it by means of points.
• The deterioration of the quality of life. If you do not take action to correct vision, farsightedness may gradually lead to the deterioration of the quality of life.
• Eye strain. When hypermetrope difficult to focus, because of which it can often experience eye strain and, as a consequence, and headaches.
• Security Risk. Farsightedness can make driving more dangerous, moving around the city on foot and some other activities.

Treatment

The main treatments for hyperopia are corrective lenses and refractive surgery. In the first case, the choice between glasses and contact lenses is carried out according to the wishes of the patient, the degree of farsightedness and the presence of his other ailments, especially - eye diseases.

In some cases, for the treatment of hyperopia Treatment of hyperopia - long-term and regular   also used refractive surgery. The main methods of refractive surgery are:

• Laser vision correction. During the operation, part of the cornea removed to correct refraction therein.
• Photorefractive keratectomy. This procedure is similar to laser vision correction, but here the surgeon removes the epithelium. After a while it will increase again according to the new corneal shape.
• Conductive keratoplasty. Change the shape of the cornea by means of exposure to RF energy. Conductive keratoplasty gives a temporary effect.

Complications of refractive surgery may be problems associated with excessive or insufficient correction, dry eye, infections, visual side effects (e.g., glare and halos around lights). In rare cases, surgery leads to loss of vision.