Ophthalmoscope

“ Numerous other instruments of precision are now in constant use, among the most wonderful of which perhaps is the ophthalmoscope, whereby we are enabled to subject the retina and the intervening media of the eye to minute visual examination. There is not an organ of the body that is not now interrogated daily in the way of physical diagnosis, and we even examine separately the secretion of each of the two kidneys. ”

“ With the left eye he could just distinguish light in the outer upper field of vision. With the ophthalmoscope only the lower fundus of the left eye could be made out, where the retinal vessels were seen up to the lower edge of the optic disk. The disk itself could not be made out, but above it a bulging, detached retina was prominent, with a hemorrhagic spot at its inner margin. In the upper outer fundus another separate bulging detachment of the retina could be plainly seen. ”

“ Notice the thinness of the retina, and, also, that the seeming iridescence of the choroid shows through. The optic disc, which is the point of entrance of the optic nerve, and the optic cup are easily recognized, though neither will be seen as large as when viewed in the living eye with an ophthalmoscope. The blood vessels of the retina, as they ramify outward or forward, after their entrance through the optic nerve through which they pass, are also very plainly seen. ”

“ But, if it be impracticable to apply the atropia, then the ophthalmoscope [5] must be resorted to, as offering the nearest approach to certainty of results when the accommodating-muscle cannot be paralyzed, because its contraction is not very likely to occur under the operation of that instrument. Thus provided, the oculist proceeds to examine the interior of the eye, and, his own eye being normal, and his own accommodation relaxed, if he sees the retina of the examined eye perfectly, he pronounces the refraction to be correct ”

“ The ophthalmoscope has become an instrument of incalculable value to the oculist. Many changes in the retina and interior of the eye, which are due to disease, can be observed and examined by means of the ophthalmoscope ”

“ The shifting of the eye with normal vision is usually not conspicuous, but by direct examination with the opthalmoscope.* When the optic nerve is observed with the ophthalmoscope, movement can be noted that are not apparent when only the exterior of the eye is regarded, it can always be demonstrated. If one eye is examined with this instrument while the other is regarding a small area straight ahead, the eye being examined, which follows the movements of the other, is seen to move in various directions ”

“ There are certain conditions of the eye which may warn any one that it is desirable that the condition of the vision ought to be investigated by the ophthalmoscope. Rapidly increasing short-sightedness is one of the most marked, and when this becomes associated with weakness of sight and loss of acuteness in the perception of small objects, the warning is very urgent. A diminution in the field of vision is another important indication of internal changes in the eye, of which only the ophthalmoscope can detect the true nature. ”

“ This modern invention, by which the interesting spectacle of the interior of the living eye can be observed, has therefore been far from proving a barren triumph of science. Many insidious maladies can thus be detected, and may be successfully treated before the organ has become hopelessly diseased. In some cases the ophthalmoscope gives the most certain evidence of the existence of obscure and unsuspected diseases of other parts of the body. ”

“ We must prohibit the use of concave glasses for a certain length of time, and must adopt active and effectual measures for subduing the atrophic inflammation. In the other patient the ophthalmoscope may show us but little stretching or waste, and that not progressive, and will enable us then to calm his fears, to prescribe appropriate glasses, and to dismiss him to his occupation with ease of mind and safety. ”

“ 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 ”

“ We must suppose a great many ophthalmoscope-drawings preserved, with notes proving that these purported to be drawings of the retina.
After society had settled down again, the drawings might begin to attract attention. Thereupon would set in fierce discussion in the medical world. There would be a tradition' that certain medical draughtsmen of the 19th century had a means of knowing what the living retina looks like; a means not accessible to ordinary men. ”

“ In fact, a piece of window-glass placed in an oblique position, as described above, is the simplest form of an ophthalmoscope, and may easily be arranged by any one who wishes to make the experiment for himself. An ordinary piece of glass is sufficient for the purpose, if placed in the same position, relatively to the eye under observation and the light, as that shown in the figure. It is well to place a screen between the light and the person under observation, to prevent any annoyance arising from the intensity of the light. ”

“ In most cases of eccentric fixation, on the contrary, the eye quickly tires, and its appearance, with that of the face, is expressive of effort or strain. The ophthalmoscope reveals that the eyeball moves at irregular intervals, from side to side, vertically or in other directions. ”

“ In the past, and even at present, with those surgeons who are content to treat deep-seated diseases of the eye by guessing at their nature, and have not adopted the systematic use of the ophthalmoscope into their practice, the functional annoyances which commonly occur at the outset of the formation of lenticular cataract, have been, and are, fertile sources of deception. ”

“ But out of this investigation, which to the practical man would appear utterly trivial and useless, came not only knowledge that shattered certain superstitious fears, but even the ophthalmoscope that every year helps to save the sight of thousands of human beings. ”

“ Atropine is universally and constantly used in ophthalmic practice in order to dilate the pupil for examination of the retina by the ophthalmoscope, or in cases where the inflamed iris threatens to form adhesions to neighbouring parts. ”

“ The retinoscope is an instrument used to measure the refraction of the eye. It throws a beam of light into the pupil by reflection from a mirror, the light being either outside the instrument—above and behind the subject—or arranged within it by means of an electric battery. On looking through the sight-hole one sees a larger or smaller part of the pupil filled with light, which in normal human eyes is a reddish yellow, because this is the color of the retina, but which is green in a cat's eye, and might be white if the retina were diseased. ”

“ Eye of Ammocœtes. The optic vesicle arises as an outgrowth of the fore-brain, but the secondary optic cup is remarkable in the young larva for its small size (fig. 291, opv) . The thicker outer wall gives rise to the retina, and the thinner inner wall to the choroid pigment. The lens is formed as an invagination of the single-layered epidermis (fig. 291, l) . As development proceeds the parts of the eye gradually enlarge, and the mesoblast around the hinder and dorsal part of the optic cup becomes pigmented. ”

“ 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. ”

“ The little sharply lighted and heated point to which the light-rays can be brought is the focus of the lens, and the distance it lies behind the lens is called the focal distance. The thicker the lens, or burning-glass, is in the middle, the shorter its focal distance, and the more strongly it will magnify.
A healthy, or normal, eye is of just such shape and "bulge" that rays of light entering the eye are brought to a focus on, or close to, the retina at the back of the eyeball. Some people, however, are unfortunately born with eyes that are too small and flat, or do not "bulge" enough ”

“ The room is made perfectly dark; a brilliant light is then placed near the head of the patient, and the rays are reflected by a series of small mirrors into his eye, as if they came from the eye of the observer; then, by looking through the central aperture of the instrument, the oculist can examine the illuminated interior of the eyeball, and perceive every detail of structure, healthy or morbid, as accurately and clearly as we can see any part of the exterior of the body. ”

“ An optometrist examines eyes for refractive error, recognizes (but does not treat) diseases of the eye, and fills prescriptions for eyeglasses. The optician is an artisan qualified to grind lenses, fill prescriptions, and fit frames.
The effect of § 2 is to forbid the optician from fitting or duplicating lenses without a prescription from an ophthalmologist or optometrist. In practical effect, it means that no optician can fit old glasses into new frames or supply a lens, whether it be a new lens or one to duplicate a lost or broken lens, without a prescription. ”

“ Simultaneous retinoscopy is difficult in the case of a reading patient, for not only is the pupil small, but in order to find the shadow it is necessary for the patient to look in one general direction all the time, and this is not easy. It is also difficult to hold a glass at one side of the eye for the measurement of the refraction in such a way that the observer can look through it while the patient does not. ”

“ 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 ”

“ The rudimentary eye would at first merely consist of cells sensitive to light, and of ganglion-cells connected with them; while at a later period optical structures, constituting a lens capable of throwing an image of external objects upon it, would be developed, and so convert the whole structure into a true organ of vision. It has thus come about that, in the development of the individual, the retina is often first formed in connection with the central nervous system, while the lenses of the eye are independently evolved from the epidermis at a later period. ”

“ 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. ”

“ Properly to determine the optical error in astigmatic and farsighted eyes it is essential to place drops in the eye, which dilate the pupil and paralyze the muscles that control the convexity of the crystalline lens, and to use instruments and methods of examination, which can only be properly undertaken and interpreted by one with the general and special medical training possessed by an oculist. ”

“ The chief lymph stream flows from the posterior chamber past the margin of the lens, through the zonula of Zinn, beneath the iris, through the pupil into the anterior chamber, thence through the tissue at the junction of the iris and sclera into the circular canal of Schlemm and from this space into the external lymph channels. Obstruction to the steady escape of the intra-ocular fluids at any point in this drainage system or any undue increase of the fluids themselves may [Pg 103] produce glaucoma. ”

“ The opacities in the cornea or aqueous, in front of the axis of vision in the lens move in the same direction and to the same degree as the eye rolls, while opacities on the posterior capsule or in the vitreous, move in a direction opposite to the motions of the eye, and to a degree corresponding to their distance back of the lens. Thus if the eye looks downward such opacities move upward; if it looks upward they move downward; if it looks inward they move outward; and if it looks outward they move inward. ”

“ When the lens has been removed for cataract the patient usually appears to lose his power of accommodation, and not only has to wear a glass to replace the lost part, but has to put on a stronger glass for reading. A minority of these cases, however, after they become accustomed to the new condition, become able to see at the near-point without any change in their glasses. The existence of these two classes of cases has been a great stumbling block to ophthalmology. ”