Astigmatism

Traslated by J.G. Provencio

bullet What is astigmatism? It is difficult to answer this question. As a start we could say that the word comes from the Greek: "a" stands for "without" while "stigma" stands for "point".
bullet People with myopia or hyperopia, according to the definitions we already know from other paragraphs, suffer of the same extent of myopia or hyperopia whichever direction they look at. An astigmatic eye, on the contrary, can see in a different way depending on the orientation.
bullet Thus, the astigmatism could be defined as follows: optic condition in which parallel light rays entering the eye are not refracted at the same extent all over the eye-meridians.
bullet In the regular astigmatism, refraction changes from one meridian to another, are progressive. Consequently, the final resultant is reduced to two major meridians: the ones with the lowest and the highest refraction power which are perpendicular.
bullet In the irregular astigmatism, or pathologic, there are no geometrical patterns to be found in the different meridians. A different power in the same meridian could happen, indeed. This last possibility is given, for instance, in eyes having been injured or corneas affected by some illness. Irregular astigmatism is much less frequent than regular one.
bullet The most usual responsible for the astigmatic defect is the cornea. In a normal eye, whatever myopic or hyperopic it is, the cornea is spherical shaped (that is, a piece of basket-ball). In an astigmatic eye, the cornea will be flattered, toric (that is, as a piece of a rugby-ball, or a flattered piece of basket-ball). The direction in which this flattering happens is which will determine the astigmatic axis.
bullet Normally, most eyes usually have an astigmatic component. The great many any correction at all is needed.
bullet SYMPTOMS. Which optic consequences does astigmatism have on what the eye can see? Well, they may change ; and they do as a matter of fact. To outline, we could say that the first result is that the image that an astigmatic-eye will make of a point, will be a line( in the direction producing the cornea flattering). This way, it happens that a line (being actually a succession of points) will be seen rather hazy by an astigmatic eye wherever the line is located in the same direction of the astigmatism of the eye. However, it will be perceived much clearer if seen in a perpendicular direction to it.
bullet Besides, both meridians can be myopic, or astigmatic; or even one of them may be astigmatic and hyperopic the other. As a result of this, symptoms vary quite a lot depending on the case. To outline again, we could say that astigmatic-myopic and astigmatic-hyperopic people can be taken as they were just myopic or hyperopic (as an overview, I insist on this). And we come to the same thing: the eye is a dynamic system and tries, by means of accommodation, to correct the astigmatic effects. Which consequence? Something close to what happened with hyperopic. The "amount" of astigmatism , the patient age—and this time the sort of astigmatism, too— can produce no visual problems at all, problems related to the near and far vision, bad near vision but only annoyance related to the far one, or even bad vision both for the far and the near vision.
bullet In addition to this, we could set different kinds of astigmatism besides the ones already given (regular-irregular, myopic- hipermetropic-mixed). Most usual ones are related to the astigmatic axis and the sort of eye. Some produce more effects and annoyance than others, but this is for a deeper analysis which is beyond our intention.
bullet TREATMENT. Astigmatism treatment is obtained using a toric lens (astigmatic) with an opposite algebraic sign so that the eye-toric shape is annulled.
bullet Generalising once more, we could say that a toric surface is more curved in one sense than in another. For example, the outer surface of half a boiled egg would be a toric surface(a piece of doughnut would do, too).

bullet Generally speaking, the small-rate astigmatisms are only treated as far as the symptoms go. Namely: if the visual keenness is good, and there are no other kind of bothers, correction is not needed. But, of course, if there is no good vision or there is an ocular fatigue, headaches or any other bother, a correction is absolutely necessary.
bullet We must note as well, that first time it is corrected astigmatism usually produces little initial bothers, say, a slightly vertigo-like feeling, clear object perception of the edges but deformed in some directions, etc. The brain should become used to new received images and little time is needed (the higher the astigmatism the longer). These bothers disappear, logically, after some days of prescription use.
bullet CONTACT LENSES. Quite recently it was said that it was not possible to correct astigmatism using contact lenses. Some slight corrections to that. Firstly, an eye with little amount of astigmatism might not tolerate the adaptation of contact lenses very well. The rest of cases worth the attempt. This could be made either by the use of spherical soft lenses (if the astigmatism is not very big compared to myopia or hyperopia), or with toric lenses— the special ones for astigmatism(already studied in other paragraph). Even hard or gas-permeable spherical lenses could be used as an attempt: the reason for the use of spherical hard lenses in order to correct astigmatism —and not the soft ones— is quite simple: We've already said that, in general, the problem of the astigmatism is the result of a "deformation" of the cornea. Thus, if we place a soft lens, it will take the form of the cornea, and the problem will be still remaining. If we place a hard one, the cornea will not be deformed, and the space laying between the lens and the cornea would be fulfilled of tear-like liquid -which would work as a lens; It is this that will create a "new spherical cornea", that is to say, without astigmatism.

EVOLUTION. Does the astigmatism go on? Well, as a general rule, it usually becomes stable when the growth is finished, and an increase is rather difficult to happen. But there are not exact rules here, and we cannot forget about a rise. Much more unlikely it is that an axis change may happen(which could be the trace of grave impairment). Finally, we cannot forget about one more factor: occasionally, there are some kinds of astigmatism that aren't noticeable —just partially or on the

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