THE EYES AND THEIR CARE

vision is the most important of the human senses we learn to see only as we practice using the eyes simultaneously with the first visual impressions infants reach for the object with their hands vision alone at this age does not give an idea of how far the object is away infants learn to judge distance in part by interpreting the stresses and strains of the eye muscles the degree of convergence of the eyes helps in determining the distance of nearby objects familiarity with the size of an object helps in estimating distance when it is beyond reach we learn to suppress vision when the eyes are in motion otherwise we would have a blur like this which would cause severe nerve strain we learn to ignore motionless objects at the edge of the visual field this helps to concentrate the attention upon the object on which our eyes are directly focused glaucoma brain tumors and inflammation may lead to a very limited field of vision like this as we contemplate partial blindness and the blind we realize more fully the importance of good vision the brows afford adequate protection to the eyes themselves the human eyes and the eyelids are things of great beauty and efficiency the eyeballs are marvelous little cameras they are globe shaped and rotate in a socket these two muscles control the up-and-down motion of the eyeball altogether six muscles control the motion and the position of the eye the sun is the most important source of light and it is by reflected light rays that objects in the environment are made visible through the eye light entering the eye passes through the cornea the aqueous humor the lens the vitreous humor and to the retina the light receptors in the retina connect with nerve fibers these fibers merge into a cable called the optic nerve which leaves the eye at the back through this same opening blood vessels arteries and veins enter the eye to supply nourishment and to carry away waste materials from the retina here the pulse is in the veins the front layer of the retina contains millions of percept ourselves rod cells shown here in black and cone cells shown in white it is these cells which transform light energy into another form of energy which is transmitted by the optic nerves to the brain the light from an object upon which we fix our gaze falls upon a small depression called the fovea where there is a thinning out of the retina here there are only cone receptors and each one has its own nerve fiber leading to the brain these cone cells have to do mainly with sharp vision and color vision toward the periphery of the retina the rods predominate these perceived dim light and light from the side without color when the light is dim the pupil opens up so as to let in more light and besides the rod cells become more sensitive and thus take over the function which the cone cells perform higher illumination when we turn off these bright lights we can see almost nothing but within a short time we are able to make out objects in the room our eyes have become adapted to the dim light vitamin A is necessary for good vision in dim light the place in the retina where the nerve fibers gather and leave the retina is called the optic nerve this area is blind because it has no rods or cones we are not conscious of this blind spot because the blind spots of the two eyes do not correspond and are located in areas of less acute vision the optic nerves one from each i unite in the midline to new nerve tracts run towards the back each contains nerve fibers from both eyes the optic fibers arrive at the primary site Center in the back part of the brain in babies the eyes turn in different directions until they learn to regard an object with both eyes working together the image should always fall on the sensitive part of the retina for distant vision the eyes look straight ahead but for near vision the eyes turn in if been looking to the side the muscle of one I fails to work we are conscious of double vision however one of the images is dim because in one eye the Rays are not focused on the fovea eventually the dim image is suppressed and finally this I may lose its ability to see clearly in some cases the good I may be bandaged so as to compel use of the suppressed I and thereby restore sharp vision the images from the two eyes are slightly different because each eye sees the object from a different position but the brain uses them into a single image many types of eye defects are caused by improper focusing of the image on the retina here the players are out of focus while the foreground spectators are in focus this is nearsightedness which results when the eyeball is too long from front to back the focus is in front of the retina this defect in vision may be corrected by wearing concave lenses when the eye is too short the image is formed back of the retina this is farsightedness by accommodating the lens proper focus may be attained but this stress may lead to discomfort that can be relieved by wearing glasses an uneven surface in the cornea or in the lens leads to this type of distorted vision called astigmatism lenses can be ground to overcome this defect bacterial infection of the I often comes from using public swimming pools from rubbing the eyes with the fingers and from using soiled towels infections may enter the lid and cause a stye the mucus lining the cornea or even the interior of the I may also be infected by way of the circulatory system if a foreign particle becomes lodged on the eyeball and especially on the cornea it should be removed by a competent person after applying a local anesthetic this doctor carefully works the particle loose and then takes it out particles of steel like this may cause severe damage to the delicate membrane afterwards the doctor washes the eye with a suitable antiseptic solution radiation from the red end of the spectrum such as heat from the Sun may penetrate the eye and injure the lens retina or nerves and lead to permanent blindness ultraviolet light does not penetrate as far but may cause injury to the cornea in this situation of contrasting light the eye is unable to adjust properly either for the bright page or the dark room this type of eye fatigue is overcome by having uniform good illumination in the entire visual field the eyes need to be protected from all types of physical injury by suitable protectors because site is our most precious sense we should guard the eyes by proper lighting proper food and by preventing disease and injury to this delicate mechanism