Hyperopia

“ The second deviation in the form of the eye is called hyperopia. This is a flat eye, a very common form in children. It is a congenital defect, in which the crystalline lens is located so near the retina that light, passing into the eye, is stopped by the retina before it comes to a focus. This must also produce an ill-defined picture. Unfortunately, faulty eyes, which give out under use, do not appear differently from perfectly shaped ones. The flattening, or the elongation, is not in the exposed cornea. ”

“ Long-sight, or hyperopia, is common among schoolchildren, nearly as much so as short-sight, and must not be confounded with the defect known as the "far sight" of old people; although in both affections the sight is improved by the use of convex glasses. Children not infrequently discover that they see much better when they chance to put on the spectacles of old persons. For the relief of short-sight, concave glasses should be employed; as they so scatter the rays of light as to bring the focus to the retina, and thus cause the vision of remote objects to become at once distinct. ”

“ 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. ”

“ It is always so for long and continuous ones. For presbyopia, there is no prevention and no cure. There is a makeshift device (spectacles) whereby we may supply the lost focusing power of the living lens, by glass lenses placed in front of the crippled 'crystalline lens.' Of cataract, however, there is a pretty sure method of prevention, and this, again, is spectacles.
The science and art of correcting or neutralizing these optical defects of the eyes—myopia, hyperopia and astigmatism—is by means of artificial optical lenses. ”

“ Here then is another source of trouble resulting from farsightedness, i. e., the not infrequent occurrence of inward "squint" occasioned by the constant use of the muscles pulling the eyes inward during accommodation for near objects. Again, inflammation of the eyelids, and sometimes of deeper parts of the [Pg 25] eyeball, follows untreated hyperopia. Early distaste for reading is often acquired by farsighted persons, owing to the strain on the accommodative apparatus. The convex lens is that used to correct farsightedness. ”

“ Vision, as determined by the official test types, must not fall below 20/40 in either eye, and not below 20/20 unless the defect is a simple refractive error not hyperopia, is not due to ocular disease, and is entirely corrected by proper glasses. ”

“ With every lessening of the distance of the object, still greater converging power is demanded, as one may understand by tests with different-power glass lenses. When the object is brought within ten or fifteen inches of the eye the greatest effort is required to make the image clear. The degree of this effort will depend upon how much too short the eyeball is, or upon the amount of hyperopia. ”

“ In the more difficult cases of presbyopia the patients often suffer from the same illusions of color, size, form and number, when they try to read fine print, as do patients with hypermetropia, astigmatism, and myopia when they try to read the letters on the Snellen test card at the distance. They are unable to remember or imagine, when trying to see at the near-point, even such a simple thing as a small black spot, but can remember it perfectly when they do not try to see. ”

“ 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. ”

“ Persons whose sight was normal while awake were found to have myopia, hypermetropia and astigmatism when asleep, and if these errors were present when they were awake, they were increased during sleep. This explains why so many people are unable to see as well in the morning as at other times, and why people waken with headaches and pain in the eyes. Under ether or chloroform, errors of refraction are also produced or increased, and when people are sleepy they have invariably been found to have errors of refraction. ”

“ 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. ”

“ On a similar principle, we should flood with diffused light the rooms in which numerous workmen are to be gathered, some of whom must be far from the windows. With a good light, or one which is equivalent to several million candles a yard off, we use in reading only a fraction of the cornea, and the contraction of the pupil has the effect of greatly diminishing the diameter of the circles of diffusion which are liable to produce in the retina faults of vision. Under these conditions, a badly formed eye may perform good service, and is subject to only a moderate degree of fatigue. ”

“ Atrophy of the optic nerve is one of a considerable number of diseases, like detachment of the retina, irido-cyclitis and absolute glaucoma, which have been placed beyond the pale of hope by the science of ophthalmology. Yet persons with atrophy of the optic nerve sometimes have normal vision, and persons blind from this cause sometimes recover spontaneously. At the New York Eye and Ear Infirmary, thirty years ago, a patient was exhibited who had all the symptoms of atrophy of the optic nerve, but who nevertheless possessed perfect sight. ”

“ One patient with two diopters of myopia may see twice as much as another with the same error of refraction. The evidence of the test card is, in fact, entirely subjective; that of the retinoscope is entirely objective, depending in no way upon the statements of the patient.
By means of simultaneous retinoscopy it has been demonstrated that the refraction of the eye is never constant; that all persons with errors of refraction have, at frequent intervals during the day and night, moments of normal vision when their myopia, hypermetropia, or astigmatism, disappears completely ”

“ Anyone who knows how to use a retinoscope may, however, demonstrate in a few minutes that both of these conditions are acquired; for no matter how astigmatic or hypermetropic an eye may be, its vision always becomes normal when it looks at a blank surface without trying to see. It may also be demonstrated that when children are learning to read, write, draw, sew, or to do anything else that necessitates their looking at unfamiliar objects at the near-point, hypermetropia, or hypermetropic astigmatism, is always produced. The same is true of adults. ”

“ In young people when the error is not too high this work is done unconsciously, vision appears to be perfect, and it is only by placing the eye under the influence of atropine that the defect is revealed. In the normal eye distant objects are focused on the retina without the use of the ciliary muscle, which is only employed when looking at near objects; but the hyperope has to use this muscle all his waking hours for both near and distant vision, so that his eyes are never at rest. ”

“ Note that in hypermetropia and myopia the rays, instead of coming to a focus, form a round spot upon the retina. The interference of the lens, however, is believed to account for only moderate degrees of variation in errors of refraction, and that only during the earlier years of life. For the higher ones, or those that occur after fortyfive years of age, when the lens is supposed to have lost its elasticity to a greater or less degree, no plausible explanation has ever been devised. ”

“ In hypermetropia11 - commonly but improperly called farsight, although the patient with such a defect can see clearly neither at the distance nor the nearpoint - the eyeball is too short from the front backward, and all rays of light, both the convergent ones coming from near objects, and the parallel ones coming from distant objects, are focussed behind the retina, instead of upon it. In myopia it is too long, and while the divergent rays from near objects come to a point upon the retina, the parallel ones from distant objects do not reach it. ”

“ Therefore, in the case of the disappearance or lessening of hypermetropia, we are asked to believe that the eye, in the act of vision, both at the near-point and at the distance, increases the curvature of the lens sufficiently to compensate, in whole or in part, for the flatness of the eyeball. In myopia, on the contrary, we are told that the eye actually goes out of its way to produce the condition, or to make an existing condition worse. ”

“ That the human eye resents glasses is a fact which no one would attempt to deny. Every oculist knows that patients have to "get used" to them, and that sometimes they never succeed in doing so. Patients with high degrees of myopia and hypermetropia have great difficulty in accustoming themselves to the full correction, and often are never able to do so. The strong concave glasses required by myopes of high degree make all objects seem much smaller than they really are, while convex glasses enlarge them. ”

“ Numerous answers to this question have been proposed, but no one has yet succeeded in finding a satisfactory one.1 In the case of children it has been assumed by many authorities that, since the coats of the eye are softer in youth than in later years, they are unable to withstand a supposed intraocular tension produced by near work. When other errors of refraction, such as hypermetropia and astigmatism, believed to be congenital, were present, it has been supposed that the accommodative struggle for distinct vision produced irritation and strain which encouraged the production of short sight. ”

“ Here the eye, as an optical apparatus, remains passive. Just as a man, who sees, is aware of the phenomena even in the deepest darkness, so is also a blind man, as long as the retina is endowed with its specific sensitiveness or sensory power, by which it responds to every irritation with a luminous sensation. Even after blindness, this dancing of sparks of fire and light may be kept up by continual irritation in the eye to such a tormenting extent, that, in order to prevent it, we usually cut the optic nerve just behind the eye, when the sparkling and scintillating cease. ”

“ This arises from an imperfection of the glass lens, called its spherical aberration, which is due to the fact that the circumferential and central rays have not the same focus. The human eye labours under a similar defect, and from this, and other causes, it arises that when the naked light from fifty cells is looked at the blur of light upon the retina is sufficient to destroy the definition of the retinal image of the carbons. A long list of indictments might indeed be brought against the eye—its opacity, its want of symmetry, its lack of achromatism, its partial blindness. ”

“ Presbyopy is principally caused by too little convexity of the cornea and crystalline lens, which throws the focal point of rays reflected from near objects, beyond the retina. This defect is experienced by most people, to a greater or less degree, after they have advanced beyond the fortieth year, and occasionally [192] even by youth. A remedy, or, at least, a palliation, is found in the use of convex glasses, which render the rays more convergent, and enable the eye to refract them to a focus farther forward, at the proper point. ”

“ The pupil of an eye appears black to an observer, because the eye of the observer does not receive any of those reflected rays. If, however, we strongly illuminate the retina, and hold a lens in front of the eye, so as to bring the reflected rays to a focus nearer the eye, then a virtual and erect, or a real and reversed, image of the retina will be seen. Such is the principle of the ophthalmoscope, invented by Helmholtz in 1851. Eyes deficient in pigment, as in albinos, appear luminous, reflecting light of a red or pink colour ”

“ IV. Of direct ocular spectra.
A quantity of stimulus somewhat greater than natural excites the retina into spasmodic action, which ceases in a few seconds. A certain duration and energy of the stimulus of light and colours excites the perfect action of the retina in vision; for very quick motions are imperceptible to us, as well as very slow ones, as the whirling of a top, or the shadow on a sun-dial. So perfect darkness does not affect the eye at all; and excess of light produces pain, not vision. ”

“ The main cause of myopia is to be found in the very conditions under which children are gathered together in schools: insufficiency of light, the over-small type common in school-books, the frequent use of the blackboard, on which the teacher is not always careful to make the size of the characters he traces proportionate to the distance at which they have to be read, are so many causes of ocular fatigue. The visual keenness of a given eye, says Doctor Leprince, decreases rapidly when the intensity of the light falls below a certain limit. ”