Retinal image

“ The presence of the iris greatly diminishes the extent of surface designed for the reception of light; the whole pencil of rays that falls on the cornea, as supposed, in Fig. 3, not reaching the retina, but only as shown in Fig. 4, on that section of it which enters the pupil. Though much of the volume of light is thereby lost, the restriction is highly beneficial, by sharpening the image on the retina; for the refraction of the rays is much more equal in the centre than toward the margin. ”

“ The estimation of color being connected with the impression produced upon the retina, it is readily to be seen that the human eye will not always equally well perform that function. The different points of the retina are not alike ready to appreciate colors. To distinguish the details of au object, it is necessary to direct the look toward it, or, in other words, to produce an image upon the central region of the retina, where the acuteness of physiological perception is much the greatest. ”

“ We may say indeed that the function of the greater part of the retina is merely to give us a general impression of the environment of the object which is being looked at; an impression, that is to say, which will enable us to judge of its relationship to other things. It tells what else there is to look at, and subconsciously we shift our gaze so that, piece by piece, the whole landscape comes to be focused on the central portion. We regard with the central portion what we know exists to be regarded on account of the duller image thrown on the rest of the retina. ”

“ In all, or nearly all, perfect eyes the lens is flatter in front than behind, and this enables us to see things far off by bringing the rays from them exactly to a focus on the retina. But when we look at nearer things the rays require to be more bent or refracted, so without any conscious effort on our part this ciliary muscle contracts and allows the lens to bulge out slightly in front. Instantly we have a stronger magnifier, and the rays are brought to the right focus on the retina, so that a clear and full-size image of the near object is formed. ”

“ Although the blurred and indefinite retinal picture may be compensated, and perhaps more than compensated, by the readiness with which the eyes move, it is, of course, possible that greater precision and delicacy of visual impression over the whole surface of the retina might be consistent with a still greater increase of our powers of perception. There are instances in which the absence of finish, as it may be termed, in all but one little spot in the picture, proves a real inconvenience and a sensible deprivation. ”

“ In recent years the use of different, established, and novel imaging techniques provided detailed insight into several retinal diseases. These modalities provide information about anatomy and functional changes in the retina with high resolution images which improve diagnosis and management of retinal pathologies. ”

“ He explains this by the supposition that the retinal impression is strengthened by the same retinal areas being rapidly and repeatedly subjected to the action of the rays of light from the same object, while a longer period of fixation would cause retinal fatigue and blur; showing the same principle by reminding us that our perceptive powers for a test object, upon first being brought into view at the periphery of the field of vision, are much stronger when the object is shaken than when it is brought quietly toward the fixation-point. ”

“ The retina is not so easily excited into action by less irritation after having been lately subjected to greater. 1. When any one passes from the bright daylight into a darkened room, the irises of his eyes expand themselves to their utmost extent in a few seconds of time; but it is very long before the optic nerve, after having been stimulated by the greater light of the day, becomes sensible of the less degree of it in the room; and, if the room is not too obscure, the irises will again contract themselves in some degree, as the sensibility of the retina returns. ”

“ In the normal human eye, only the central parts of the retina are sensitive to colour, the peripheral parts are practically colour-blind. Anæmia of the retina, which may be produced by pressure on the eye-ball, will render the retina, first colour-blind and then insensitive to light. ”

“ Were it not for the retina there would be no color; and when the sensory nerves of the retina are partially paralyzed or deficient, as in the case of the color-blind, nature appears to the eye in her true monochromatic garb.
The human eye resembles closely the photographic camera, both in structure and in its manner of functioning. ”

“ Its finest fibers are ultimately connected with numerous elongated cells which are stimulated by light. The retina is dark purple in color, this color being caused by a layer of cells next to the choroid coat. This [Pg 361] accounts for the black appearance of the pupil of the eye, when we look through the pupil into the darkened space within the eyeball. The retina acts as the sensitized plate in the camera, for on it are received the impressions which are transformed and sent to the brain as sensations of sight. The eye, like the camera, has a lens. ”

“ For the most part there will be nothing beyond a confused idea of light and shade. The time of this momentary vision will be too short to enable the human retina to perceive or the human brain to register any definite impression of anything.
How is it with the photographic camera and lens, our artificial eye? We will suppose that everything is in readiness, that its retina or sensitive plate is in perfect condition, and that not a ray of light has yet entered within the darkened chamber. ”

“ 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. ”

“ The eye—which sees all objects reversed—retains the images for some time. This conclusion is proved by the results; because, the eye having gazed at light retains some impression of it. After looking (at it) there remain in the eye images of intense brightness, that make any less brilliant spot seem dark until the eye has lost the last trace of the impression of the stronger light. ”

“ It is impossible that the eye should project from itself, by visual rays, the visual virtue, since, as soon as it opens, that front portion [of the eye] which would give rise to this emanation would have to go forth to the object and this it could not do without time. And this being so, it could not travel so high as the sun in a month's time when the eye wanted to see it. ”

“ THE BODY WHICH IS NEAREST TO THE LIGHT CASTS THE LARGEST SHADOW, AND WHY? If an object placed in front of a single light is very close to it you will see that it casts a very large shadow on the opposite wall, and the farther you remove the object from the light the smaller will the image of the shadow become. ”

“ High above his birthplace the snowy Alps paint themselves against the sky, an aerial dream of beauty, softened by the tender hues of dawn and sunset, serenely fair through the rift of the tempest; even their white death takes a nameless grace from distance and atmosphere, clothing itself in beauty as a spirit in clay, and tempting wanderers to their graves: but no such beauty clothes the man whose daily vision beholds them; hard, clamorous, disputatious, with one hand he rends the rotten splendors of Rome from its tottering Image, and with the other plunges baby-souls to inevitable damnation ”

“ The eyes of some persons are large, others small, and others of a moderate size—the last-mentioned are the best. And some eyes are projecting, some deep-set, and some moderate, and those which are deep-set have the most acute vision in all animals; the middle position is a sign of the best disposition. ”

“ The eye is continually influenced by what it cannot detect; nay, it is not going too far to say, that it is most influenced by what it detects least. Let the painter define, if he can, the variations of lines on which depend the changes of expression in the human countenance. ”

“ For the eye is always in search of beauty, and if we do not gratify its desire for pleasure by a proportionate enlargement in these measures, and thus make compensation for ocular deception, a clumsy and awkward appearance will be presented to the beholder. ”

“ The eye which turns from a white object in the light of the sun and goes into a less fully lighted place will see everything as dark. ”

“ millions of millions of vibrations have penetrated the eye before the eye can distinguish the tints of a violet. ”

“ Our flesh shrinks from what it dreads and responds to the stimulus of what it desires by a purely reflex action of the nervous system. Our eyelid closes before we are aware that the fly is about to enter our eye. ”

“ This human nose, for instance, of which no philosopher has yet spoken with reverence and gratitude, is, for the present, the most finely adjusted instrument at our disposal: it is able to register even such slight changes of movement as the spectroscope would be unable to record. ”

“ No small hole can so modify the convergence of rays of light as to prevent, at a long distance, the transmission of the true form of the luminous body causing them. ”

“ I ask how far away the eye can discern a non-luminous body, as, for instance, a mountain. It will be very plainly visible if the sun is behind it; and could be seen at a greater or less distance according to the sun's place in the sky. ”

“ All objects transmit their image to the eye in pyramids, and the nearer to the eye these pyramids are intersected the smaller will the image appear of the objects which cause them. ”

“ I think it was his eye! yes, it was this! One of his eyes resembled that of a vulture—a pale blue eye, with a film over it. Whenever it fell upon me, my blood ran cold; and so by degrees—very gradually—I made up my mind to take the life of the old man, and thus rid myself of the eye for ever. ”

“ That light is not itself a substance may be proved from the phenomenon of interference. A beam of light from a single source is divided by certain optical methods into two parts, and these, after travelling by different paths, are made to reunite and fall upon a screen. If either half of the beam is stopped, the other falls on the screen and illuminates it, but if both are allowed to pass, the screen in certain places becomes dark, and thus shows that the two portions of light have destroyed each other.
Now, we cannot suppose that two bodies when put together can annihilate each other; ”

“ all the rays which convey the images of objects through the air are straight lines. Hence, if the images of very large bodies have to pass through very small holes, and beyond these holes recover their large size, the lines must necessarily intersect. ”

“ Colour-blindness always extends to the complementary colours. Those who are red blind are also green blind; those who are blind to blue have no consciousness of yellow. This law holds good for all mental phenomena; it is a fundamental condition of consciousness. ”

“ Is it not curious, that so vast a being as the whale should see the world through so small an eye, and hear the thunder through an ear which is smaller than a hare’s? But if his eyes were broad as the lens of Herschel’s great telescope; and his ears capacious as the porches of cathedrals; would that make him any longer of sight, or sharper of hearing? Not at all.—Why then do you try to “enlarge” your mind? Subtilize it. ”

“ I dislike an eye that twinkles like a star. Those only are beautiful which, like the planets, have a steady, lambent light;--are luminous, but not sparkling. ”

“ And from the height of this perception all that had previously tormented and preoccupied him suddenly became illumined by a cold white light without shadows, without perspective, without distinction of outline. All life appeared to him like magic-lantern pictures at which he had long been gazing by artificial light through a glass. Now he suddenly saw those badly daubed pictures in clear daylight and without a glass. ”

“ Lovely eyes in colour, lovely eyes in form—large and tender and quietly thoughtful—but beautiful above all things in the clear truthfulness of look that dwells in their inmost depths, and shines through all their changes of expression with the light of a purer and a better world. ”

“ it ought to underlie her silks and embroideries, but not to show itself too staringly on the outside.—You don't know, perhaps, but I will tell you; the brain is the palest of all the internal organs, and the heart the reddest. Whatever comes from the brain carries the hue of the place it came from, and whatever comes from the heart carries the heat and color of its birthplace. ”

“ And she in heaven is placed,
Yet follow her whose light the world reviveth!
Follow those pure beams, whose beauty burneth!
That so have scorched thee
As thou still black must be,
Till her kind beams thy black so brightness turneth.
Follow her, while yet her glory shineth!
There comes a luckless night
That will dim all her light;
And this the black unhappy shade divineth.
Follow still, since so thy fates ordained!
The sun must have his shade,
Till both at once do fade,—
The sun still proud, the shadow still disdained. ”