Astigmatism is one of the most complex diseases in correcting vision defects, and at the same time it is the most common among different population groups.
Astigmatism can be combined with myopia and hyperopia, and the most acceptable in most cases is correction with the help of special glasses, the lenses of which compensate for visual dysfunctions.
If you translate the meaning of the word "astigmatism" from Latin, it is not difficult to understand what it means to the absence of a focal point. Due to the wrong structure of the cornea or the lens, their sphericity is disturbed, and the resulting image is perceived as distorted.
Points for astigmatism is not easy to pick up, because a person can not see both close and far-away objects, and it turns out that for these cases two different pairs of glasses are needed.
For today there are so-called progressive - bifocals lenses for glasses, which combine two functions - vision correction for myopia and for farsightedness.
How to choose glasses with astigmatism?
For the first time the idea of combining two types of lenses came to Benjamin Franklin, who was tired of changing two pairs of glasses. In 1780 he took two different lenses for distance and near, cut them and inserted them into the frame. The top place was occupied by the lens for farsightedness, and from below for myopia . This was a new step in ophthalmology - now people have the opportunity to use one glasses to solve two problems at once. Of course, since 1780 the situation has changed somewhat, and the glasses have been improved, but the very idea of Benjamin has remained to occupy a leading place in the creation of bifocals.
Selection of glasses with astigmatism is not an easy task, for successful implementation of which several factors should be taken into account:
- age of the patient;
- degree of astigmatism;
- individual perception of lenses with correction of varying degrees.
During the practice, physicians found that patients with astigmatism can very hard to bear wearing corrective lenses - they have a headache, dizziness, and pain in the eyes. The older the patient, the more likely that the bifocal spheroprismatic glasses will bring discomfort.
Therefore, for the beginning the patient is offered to wear glasses that do not completely correct the vision, and only after a few months they suggest putting on "strong" lenses that compensate for the visual defects 100%.
By "complex glasses with astigmatism," physicians understand lenses with an unevenly curved surface. Since the cornea and the lens are irregular in this disease, in order to normalize the perception of the image, you need to make a special lens that will compensate for the impaired shape. With a simple astigmatism, the lens is like an oval, not a sphere -
Correction of simple astigmatism
A cylindrical lens is used to correct a simple astigmatism, in which refraction is disturbed only in one meridian, and depending on this, it can in turn be collecting or scattering. A cylindrical lens is not similar in its effect to the usual spherical lens, because it does not refract light rays that fall parallel to its axis. With it, only the rays that fall perpendicular to the axis are refracted.
Correction of complex astigmatism
With mixed or complex astigmatism, toric lenses are used, in which cylindrical and spherical lenses are combined. In this case, each of the directions of refraction (they are different) has its validity.