What is astigmatism? It is difficult to answer this question. To begin we will say that is a word derived from the Greek, and that the "a" means "without", while "stigma" means "point"
A myopic or hyperopic, as we defined in other sections, are nearsighted or farsighted alike in every way, in all directions. Astigmatic eye, however, looks different depending on the orientation.
Thus, we can define the astigmatism, as the optical condition in which parallel light rays that affect the eye are not refracted equally in all of the same meridians. The regular astigmatism refractive changes from a meridian to another because it is progressive, so at the end result is reduced to two principal meridians, of higher and lower refractive power and mutually perpendicular.
In the irregular astigmatism or pathological, there is a geometric pattern in different meridians, and may even have different powers in the same meridian. The latter case occurs, for example in eyes that received injuries or corneas affected by some kind of disease, being less freciente that regularly.
The most common defect responsible is astigmatic cornea. In a normal eye is nearsighted or farsighted, the cornea is spherical (ie like a piece of basketball). In an astigmatic eye, the cornea is flattened, ring (that is like a piece of rugby ball, or a piece of basketball crushed) crushing address that determines the axis of astigmatism.
Generally, most of the eyes have a slight astigmatic component, which in most cases does not require correction.
SYMPTOMS and optical astigmatic consequences over the eye? Well they can, and in fact vary. Generalizing, we can say that the first consequence is that the image of a point of an astigmatic eye, will see a line (in the direction that determines the flattening of the cornea). Thus, it happens that a line (which is actually a sequence of points), an astigmatic eye will see very blurry if it is located in the direction of your astigmatism, and much sharper if it is in the direction perpendicular to it.
But also, it turns out that both principal meridians can be myopic, astigmatic or both, or even a nearsighted and one farsighted, so Varin symptoms enough of each other. Returning to generalize we can say that the myopic and hyperopic astigmatism can apply to the same symptoms that myopia or hyperopia (Generally speaking, again). But back to business as usual: the eye is a dynamic system and try for yourself, and using for this accommodation, correct the effects of astigmatism. The consequences? Something similar to what happened in hyperopia.
Depending on the number, age and, in this case, the type of astigmatism, may not affect vision, cause discomfort to the nearby discomfort for the near and far, poor near vision and discomfort for the distance, or even poor vision for distance and near.
We may establish different classifications of astigmatism, plus we've been naming (regular-irregular, myopic, hyperopic, mixed). The most common may be along the axis of astigmatism, and the type of each eye separately. Some produce more effects and discomfort than others, but this object would be a much deeper case of study of what is intended here.
CORRECTION Astigmatism correction is performed with a toric lens (astigmatic) opposite algebraic sign, so the toric ring of the eye.
Generalising once again, we can say that a toric surface is a surface curved in one direction than another. For example, the outer surface would be a half egg toric surface (Also, a piece of "donuts" or donut would be.
In general, only small astigmatism are corrected according to the presenting symptoms. That is, if visual acuity is good, and no other discomfort, no correction is necessary.
But, logically, if there isn't a good vision or eyestrain, headaches or other discomfort, a correction is essential.
We also note that the astigmatism corrected first initial discomfort usually produce some dizziness, and can see objects sharp but deformed at some points. The brain must get used to the new image received, and needs time for it (the greater the higher the degree of astigmatism). These complaints disappear, logically, after a few days of the correction.
CONTACT LENSES Until recently it was said that it was not possible to correct astigmatism with contact lenses. Well, we have to clarify some things. In principle, an eye with a small amount of astigmatism don't tolerate contact lens fitting. In other cases it is possible to attempt the adaptation of contact lenses. And you can do with soft lenses (if the astigmatism is not very large in relation to myopia or hyperopia you have, or with toric lenses, especially for astigmatism, and already study in another section). And even could be corrected with rigid or semi-spherical lenses. The reason astigmatism can be corrected with rigid spherical lenses and soft is simple: We have said that, in general, the problems of astigmatism arises by a "deformation" of the cornea. If we place a soft lens, this takes the shape of the cornea, keeping the problem. If we place a rigid, it is not deformed, completely filling the space between the lens and cornea to tear fluid, which makes the effects of lens, creating a "new cornea" spherical, ie without astigmatism.
EVOLUTION Can astigmatism progress? Usually it stabilized when the growth process finishes, and it is difficult to increase, but since there are no exact rules, an increase is not disposable therein. What certainly is more likely is a change of axis (and this may be a sign of serious problems). Also do not forget a fact: Astigmatism sometimes don't show either part or entirety until there are certain factors (age, occupation change, etc.)