Human eyes are two equal and symmetrical organs, positioned in the two orbital cavities of the skull.
The outer surface of each eye is a partial and opaque sphere constituted for 93% by the sclera, which IN FRONT stops giving origin to a second smaller transparent spherical portion (7% of the total area) and of different curvature, the cornea.
In the sclera there is a pigmented and vascularized layer connected to the choroid: they form the ciliary body and the iris, which is a membranous disc with a central hole (pupil) of which the diameter is adjusted by the iris muscles.
The three pigmented portions form the uveal tract or uvea. Deeply the choroid extends a photosensitive layer (retina) that ends at the junction between choroid and ciliary body.
It contains the eye photoreceptors that convert light into electrical potentials sent through the optic nerve and the visual pathway as far as the brain regions associated with the view.
The ciliary body is connected at the zonular fibers that attach to the lens to the ciliary body that changes shape through his muscles and focus.
Inside the eye there are also three rooms.
The anterior chamber is the space between the cornea and the iris, the posterior chamber is between the iris and the lens, and finally the large vitreous chamber behind the lens.
The first two are filled with ‘umore acqueo’, a clear liquid produced by the ciliary body that flows through the Schlemm's canal into scleral veins, instead of the vitreous cavity is occupied by the vitreous humor, a gelatinous mass that helps to determine the shape of the eyeball , occupying two-thirds of its volume.
The eye can be compared to a camera; the lens is made from lenses that allow you to focus on the images thanks to an autofocus system.
The information is then recorded on a video cassette (Retina) and transmitted via a cable (Optic Nerve).
The eye, however, differs from the camera because the images are clearly seen only in a small area of the retina: the Macula. Normally we do not perceive this because the brain always points to the macula on the object to be recognized. The remaining part of the retina allows a less defined but wider vision. This way guarantees the fundamental visual field for orientation.
VIEW UNITS OF MEASURE:
DIOPTER
Is the unit of measurement of the power of the lens shade.
Higher will be the value in diopters of a lens, more this will lessen or magnify images. The diopter should not be confused with tenths: you can see 10/10 with over 20 diopter lens. Astigmatism is expressed with an additional number that needs the direction of the lens orientation.
TENTHS
The visual acuity of the eye, also called "Visus", is the ability to distinguish the small details. Usually the normal visual acuity is expressed as a decimal. The normal value is 10/10.
The tenths are measured by counting the number of rows read on special tables called "Optotypes".
In case of defects of view there is a reduced visual acuity for distance and / or to close.
With the use of glasses or other techniques you can bring the visual acuity at an optimal level. Some diseases can cause reduced vision a few tenths, despite the use of glasses. In these cases a specialized control must examine the possibility of cure or rehabilitate in a timely manner the visual capabilities.
NORMAL VISION
It is called emmetropia the condition for which a normal eye sees well without any correction and the outside world images you focus precisely on the retina.To well see close things, eye needs a focusing system (similar to autofocus cameras) that is made from crystalline.
VISION DEFECTS
The underlying figures show a schematic representation of the vision defects, also called refraction defects, and explain in a simple but consistent way because, sometimes, the eyes do not see well.
In case of myopia the eye grows more than expected in length causing the images placed in the distance are centered in front of the retina, in the vitreous . The myopic has trouble looking in the distance, but can clearly see objects at near distances. Being myopia due to a greater elongation of the eye can occur that it tends to increase with the growth of the organism. Very often, in fact, myopia occurs after 10 years of age, during puberty, to evolve in the following years.
The causes are not well known but certainly are hereditary factors, constitutional and environmental. In industrialized countries the incidence of myopia is certainly greater: for this reason it attaches a central role, but not unique, the more time that in these countries is devoted to reading.
HYPERMETROPIA is the opposite of myopia. It is due to a too short compared to the normal eye. It is a frequent defect in early childhood when the eye is not yet grown.Theoretically hypermetropes should see bad from afar that closely because the image is focused behind the retina. Fortunately the crystalline in this case is able to compensate the defect, especially from a distance. So often the hyperopic is a person who see well, but can cause eyestrain, especially when look closely.
The astigmatism is a defect due to the fact that the cornea, the main lens of the eye, is deformed. Normally it should have a spherical shape as a soccer ball, but sometimes it becomes more flattened oval as a rugby ball. The consequence of this is that you will see distorted images. For slight astigmatism disorders are modest and often only limited to a visual fatigue; for high astigmatism you will have, however, difficulties to see both distance and near. Often astigmatism is present in the first few years of life and, if not corrected, can be very detrimental to the vision of a child.
The Presbyopia is a physiological defect that usually appears after about 45 years. The crystal grows old with age and becomes less efficient in focusing on objects, especially since they are closer. The problem can be solved with the aid of glasses that are to be used only for close-up activities. Bifocal or multifocal lenses can provide good vision at different working distances without having to change glasses.
TIPS TO KEEP THE WELLNESS OF EYES
There are many factors that affect the wellness of the eyes: some, such as diet and lifestyle, are controlled by us, others such as aging and genetic predisposition, are inevitable.
Here are some good rules to reduce the negative effects that a superficial behavior could lead the visual system.
Periodic checks: be examined by a specialist every 1-2 years. Perform regular physical exercise: cardiac and vascular stress, as in the case of high blood pressure, can cause damage to the visual system.
Treating the diet is a good rule to have a diet low in fruit and rich animal fats, cereals and vegetables, especially green leafy. If this is not possible, it's useful to take food supplements specifically designed to "integrate" the lacking elements essential to the maintenance of eye health. It is also important to keep the body hydrated by drinking 1.5 to 2 liters of water a day.
Protect your eyes from the sun: sunlight, especially ultraviolet light (UV) has been associated with many ocular disorders. In outdoor activities always wear sunglasses with 100% protection against UV-A and UV-B. Useful is also the use of a hat with a visor.
Give up smoking: smoking cigarettes as well as harmful to health and to the portfolio, also involves a large number of more or less serious eye diseases.
Protect eyes: ocular trauma often cause considerable suffering. Use eye protection in high-risk situations; for example during work or during sports
The importance of proper eye health.
A clean eye is an healthy eye.
The first effective eye defensive barrier is formed by the eyelids, eyelashes and tears. Tears "wash" the majority of substances or bacteria that try to attack the ocular surface. However, it is necessary to apply different rules of hygiene to reduce the risk of infection. The daily ocular hygiene is very important. The use of sterilized gauze is recommended for cleaning sensitive eye.
Ocular hygiene of VDT users: in the presence of noise lubricate the eye with supplements of the tear film and, at the end of the working day, gently wipe the eyelid area.The importance of a constantly lubricate the eye:The tear is a vital element for the wellness of the eyes.
The tear fluid supplies oxygen to the cornea, protects against most substances or bacteria that try to attack the ocular surface, it contributes to the clarity of vision and relieves all discomforts related to dry eye sensation (burning, foreign body sensation, etc .).
In the case of time spent staring at a source or a point at a constant distance (Videoterminals, reading, driving vehicles) blink is reduced by up to 3 times.
In these cases it is necessary to integrate the film scarcely tear product or badly distributed on the ocular surface with appropriate products, especially when these situations are frequent in the day, or take up much of our time.
