Astigmatism

“ But it, after we have got the object glass properly squared to the axis of the tube or the line of sight, the image and the ring system in and out of focus still appear oblong, the fault of astigmatism must exist either in the objective, the eyepiece, or the eye. The chances are very great that it is the eye itself that is at fault. ”

“ The effect is very well shown by the diagram, Fig. 17. To most persons the lines occupying the middle portion will appear either much blacker or much lighter than those at the two ends, though in fact they are exactly alike. When this form of astigmatism is excessive, it may be corrected by the use of spectacles fitted with cylindrical lenses.
Fig. 17.—Effect of Astigmatism.
But there is a different kind of [Pg 115] astigmatism—irregular astigmatism it is called—to which every one is more or less a victim, and which cannot be relieved by any artificial appliances. ”

“ The only certain method of detecting and consequently correcting a low error of astigmatism, in all below the age of 50, is by paralysing the ciliary muscle with atropine or homatropine and thus preventing it from correcting the defect, and revealing the true refraction of the eye. Astigmatism is corrected by cylindrical glasses combined with spherical convex, or concave glasses if hyperopia or myopia co-exist, and the correction must be worn always in the form of rigid pince-nez or spectacles. ”

“ Immediate Production of Myopia and Myopic Astigmatism in Eyes Previously Normal by Strain to See at the Distance Boy reading the Snellen test card with normal vision. Note the absence of facial strain. The same boy trying to see a picture at twenty feet. The effort, manifested by staring, produces compound myopic astigmatism, as revealed by the retinoscope. In an eye with previously normal vision a strain to see near objects always results in the temporary production of hypermetropia in one or all meridians. ”

“ The fact is that it sometimes produces myopia, or changes hypermetropia into myopia, and that it will produce both myopia and hypermetropia in persons over seventy years of age, when the lens is supposed to be as hard as a stone, as well as in cases in which the lens is hard with incipient cataract. Patients with eyes apparently normal will, after the use of atropine, develop hypermetropic astigmatism, or myopic astigmatism, or compound myopic astigmatism, or mixed astigmatism.2 In other cases the drug will not interfere with the accommodation, or alter the refraction in any way. ”

“ This astigmatism due to fault of figure must not be confused with the astigmatic difference of the image surfaces referred to in Chapter IV which is zero on the axis and not of material importance in ordinary telescopes. Astigmatism of figure on the contrary is bad everywhere and always. It should be especially looked out for in reflecting surfaces, curved or plane, since it is a common result of flexure. ”

“ With a glass to replace the focusing power of the lens – convex 7.00D.S. combined with convex 3.00 D.C., 75 degrees – she was able with this eye to read 20/40, and on the same day, after palming and swinging, she obtained temporary normal vision in both eyes, the left eyeball having elongated sufficiently to compensate for the loss of the lens. The fact that astigmatism should have developed in the right eye after the injury to the left is interesting, as astigmatism has been supposed, until recently, to be congenital. ”

“ Astigmatism is another defect in the focusing power of the eye. In astigmatism the parts of the eye fail to form the image in the same plane, so that all portions of the object do not appear equally distinct. ”

“ Small differences of this kind are found in almost every eye, but are not perceived. Higher degrees of astigmatism, which decidedly disturb vision, are, however, not uncommon, and are, therefore, also found among painters. ”

“ Suffering from mixed astigmatism and pronounced insufficiency of the internal recti muscles, which we oculists denominate an exophoria. Patient suffered terribly from headaches, almost daily in their occurrence, frequently with nausea. The muscular trouble was cured by the use of prisms, the mixed astigmatism corrected by a glass, and there remained a severe backache. It was located in the small of the back as if there were a heavy weight pressing there; worse during menses, with bearing-down pain; patient was obliged to sit down frequently, on account of the ache. ”

“ Such a patient can see upright lines, which predominate over all others in civilized life, especially in those who read much, only by holding the head to one side. When the axis of astigmatism is about 75° the head must be canted to the right to see plainly. ”

“ If the oval fringes still persist and the longer axis follows the lens, astigmatism may be inferred. Similarly, by rotating one lens on the other, astigmatism, or want of centering (quite a different thing) may be localised to the lens.
C. The presence of flexure may be confirmed by altering the position of the points of support with respect to the eyepiece, the lens maintaining its original position. The addition of more points of support will in general reduce the ill effects. How to get rid of them I do not know; they are only serious with large lenses. ”

“ Persons whose refraction is normal when they are awake will produce myopia, hypermetropia and astigmatism when they are asleep, or, if they have errors of refraction when they are awake, they will be increased during sleep. This is why people waken in the morning with eyes more tired than at any other time, or even with severe headaches. ”

“ It will be remembered that the average degree of astigmatism with the artist's examined was found to be 0·83 of a dioptre, and for this experiment I have chosen one of the lenses which is very nearly the same strength. Of course, the effect is magnified, as the camera is larger than the eye. But the eye can recognize differences infinitely more minute than those which it is possible to reproduce here, and the physiological distortion is even greater than that which it is possible to represent on the printed page. ”

“ But if this appearance is not present then irregular astigmatism cannot be proved. It is purely intentional, or a play upon words, if we refer an existing defective sight to an optic cause which cannot be proved. For instance, if haziness of the cornea exists, it is not difficult to learn to estimate by practical experience whether the amount of visual disturbance corresponds to the optic irregularities caused by the opacities and irregular refraction of the cornea. Slightly nebulous corneæ with disproportionately bad vision were therefore included in the following statistics ”

“ In many cases, if the visual acuity in each eye be made normal, the fusion impulse alone will be sufficient to restore compensation.
Many cases of esophoria result from overstimulation of the centers for convergence and accommodation, made necessary by hyperopia and astigmatism, entirely disappearing when glasses abolish the need of accommodation. Cases of exophoria are sometimes due to the abnormal relaxation of accommodation and convergence which secures the best distant vision in myopia. ”

“ Patients with high degrees of astigmatism suffer some very disagreeable sensations when they first put on glasses, for which reason they are warned by one of the "Conservation of Vision" leaflets published by the Council on Health and Public Instruction of the American Medical Association to "get used to them at home before venturing where a misstep might cause a serious accident."2 Usually these difficulties are overcome, but often hey are not, and it sometimes happens that those who get on fairly well with their glasses in the daytime never succeeded in getting used to them at night. ”

“ For an error of refraction is simply a nervous condition, and there is nothing more contagious than nervousness. A person with myopia, hypermetropia, or astigmatism, is a person under a strain. This strain shows in his voice, his walk, his manner, and makes the people with whom he comes in contact nervous. These people then develop errors of refraction, temporarily if the influence is temporary, and permanently if the influence is permanent, as in the case of children who cannot escape from their nervous teachers and parents. ”

“ The percentage declines as the children become older, but hypermetropia, or hypermetropic astigmatism, remains at all ages the most common of all errors of refraction. Hypermetropia is, in fact, a much more serious problem than myopia, or nearsight. ”

“ That is, the eye either becomes entirely hypermetropic, or some form of astigmatism is produced of which hypermetropia forms a part. In the hypermetropic eye the hypermetropia is increased in one or all meridians. When the myopic eye strains to see a near object the myopia is lessened and emmetropia1 may be produced, the eye being focussed for parallel rays while still trying to see at the near-point. ”

“ Later he called on a prominent eye specialist who told him that the presbyopia and astigmatism from which he had suffered were incurable, and that if he persisted in going without. his glasses he might do himself great harm. The fact that his sight was perfect for the distance and the near-point without glasses had no effect upon the specialist, and the patient allowed himself to be frightened into disregarding it also. ”

“ What is the percentage of improvement in each eye? 3. In your experience, when astigmatism has been cured, how does it go—all at once, or gradually? 4. Do you think I have made enough progress to warrant my continuing, or should I go back to glasses, which always gave me comfort, and leave perfect eyesight for those more easily cured? ”

“ And no spectacles will correct the mental astigmatism of the multitude, a fact that is often a cause of considerable annoyance to the possessors of normal sight. That defect of vision, whether congenital or induced by the confinements of early training, persists and increases throughout life, like other forms of myopia. ”

“ Such glasses produce an optical effect only in one direction. If instead of white lines I make the experiment with colored lines, it will show the mixing of colors produced by astigmatism; and if I now turn the axis of the lens, you will observe the effect of different forms of astigmatism. I show you a square (Fig. 3) : if I add a cylindrical concave glass, with its axis placed horizontally, the square becomes an oblong. ”

“ The author affirmed, as the readers of this magazine already know, that errors of refraction—myopia, hypermetropia, and astigmatism—so far from being permanent conditions due to deformities of the eyeball, congenital or acquired, and only to be corrected by glasses, are caused by a vicious contraction of the outside muscles of the ocular globe and may be cured by treatment leading to the relaxation of these muscles: In a word the eyeball is not inextensible, and the lens is not a factor in accommodation. ”

“ By a curious paradox, however, it often happens that the headache due to eye-strain is caused not by the grosser defects, such as interfere with vision so seriously as absolutely to demand the wearing of glasses to see decently, but from slighter and more irregular degrees and kinds of misshapenness in the eye, most of which fall under the well-known heading of astigmatism. ”

“ Other eyes which do not focus clearly on objects near at hand are said to be farsighted. Still another eye defect is astigmatism, which causes images of lines in a certain direction to be indistinct, while images of lines transverse to the former are distinct. Many nervous troubles, especially headaches, may be due to eye strain. We should have our eyes examined from time to time, especially if we are subject to headaches. ”

“ The arguments for upright writing are incontestably strengthened by some facts I have lately discovered as to the frequent influence of an axis of astigmatism in the dominant eye varying by about 15° from 90°, in producing a habitual canting or sideways inclination of the head. ”

“ The cause is found in some [pg 385] difference in curvature of the surfaces of the cornea or crystalline lens. It is corrected by lenses so ground as to correct the particular defects present in a given eye.
Whenever defects in focusing are present, particularly in astigmatism, extra work is thrown on the ciliary muscle as well as the muscles that move the eyeballs. The result is frequently to induce a condition, known as muscle weakness, which renders it difficult to use the eyes. Even after the defect in focusing has been remedied, the muscles recover slowly and must be used with care. ”

“ When relaxation is complete the patient sees, when palming, a black so deep that it is impossible to remember or imagine anything blacker, and such relaxation is always followed by a complete and permanent cure of all errors of refraction (nearsight, farsight, astigmatism and even old sight) , as well as by the relief or cure of many other abnormal conditions. In rare cases patients become able to see a perfect black very quickly, even in five, ten or fifteen minutes ”

“ All persons, without exception, who can see or read diamond type at the near-point, no matter how great their myopia may be, or how much the interior of the eye may be diseased, become able, as a rule, to see black with their eyes closed and covered more readily than patients with hypermetropia or astigmatism ”