What is myopia and hyperopia and how to distinguish between them
The eye is a sensory organ, thanks to which we can orient ourselves well in space. Eyes give the most complete information about the world around us, which is why when people have visual impairment, they begin to feel less confident and disoriented. The most common visual disturbances are farsightedness and nearsightedness.
The eye, as the organ of vision, is represented by the eyeball and the optic nerve. Movement of the eyeball is possible in several directions - up-down, right-left and in a circle, thanks to the presence of six eye muscles.
Due to what the eye sees
The flow of light is consistently progressing through several kinds of media. So, at first light passes through the cornea, then through the front and back chamber with liquids, then through the lens and the entire thickness of the vitreous body and, finally, gets on the retina. The best place for the perception of the object is the yellow spot and the central fossa, they are on the retina strictly opposite the pupil and slightly above the exit point from the eye of the optic nerve. It is in this place that the image of objects is focused.
Blind spot does not participate in vision, but it is not noticeable to a healthy person due to image compensation by the second eye and brain structures. We must proceed from the fact that in each eye the location of the blind spot is slightly different, but this is invisible because of the synchronous operation of both eyes.
On the retina of the eye the image is transmitted in an inverted and reduced form, but at the same time it accurately recreates all the details of the subject under consideration. For a clear vision, a change in the curvature of the lens due to tension or relaxation of the ciliary muscle is necessary. Normal, clear vision is called emmetropic, while the rays of light that pass through all the environment of the eye are focused clearly on the retina. But the change in the focus of the subject is called ametropia.
What is hyperopia and myopia
With age, the ciliary muscle loses its elasticity, and can not be sufficiently strained or contracted, and, accordingly, can not adequately change the curvature of the lens. And the lens itself becomes less elastic and more difficult to change. As a result, these factors lead to the fact that a person begins to see badly.
What is the difference between myopia and hyperopia? With farsightedness, a person can clearly see into the distance, but does not clearly see objects that are at close range, and with myopia everything is exactly the opposite - near objects are clearly visible, and the vision in the distance is very blurry, as if in a fog. And another difference - farsightedness is usually due to age-related changes, and myopia is often genetically determined, due to which it often manifests itself in adolescence.
Typically, age changes affect the ability to clearly see objects at close range. In order to read the text or to consider an object, a person is forced to distance himself from the eye. This is called hyperopia, i.e.a person sees far enough well, but near him he has an indistinct, blurred vision.
Such dystrophic-atrophic processes in humans begin with about 35-40 years and correct them possibly with the help of medical glasses or lenses. To correct vision, you need convex lenses on both sides, which will allow focusing the vision not just behind the retina, but precisely on it. Such glasses should be worn by a person only when reading, writing or doing fine handmade work.
Among the reasons that lead to hyperopia or, as it is called by ophthalmologists - hypermetropia, in addition to age-related changes in the eye structures, there may be a shortening of the eyeball in an anteroposterior direction. An interesting fact - in all newborns there is hypermetropia, which occurs as the child grows and the size of the eyeball increases. The age-related change in visual acuity towards a deterioration in the vision of related objects is called presbyopia.
But myopia, or myopia, develops because of the lengthening of the eyeball, because of what the image can not focus on the retina, it is going to a point earlier, in the vitreous. Rather, the image is focused in the same place as in a healthy person, but because of the greater length of the eyeball, the retina is pushed aside. Therefore, when examining distant objects there is a strong blurred vision.
Sometimes myopia is not due to an elongated eyeball, but because of the greater, than normal, refractive force of the optical media of the eye. Also, nearsightedness occurs with spasm of the ciliary muscle, when the lens can not adequately change its curvature, with a change in the curvature of the cornea, in addition, with injuries with a lens shift. Most often, these pathologies occur at a young and young age.
For correction of vision, medical glasses with biconcave lenses are necessary. They allow you to focus the image accurately on the retina.
Usually myopia is accompanied by an increase in the longitudinal dimensions of the eyeball, and this, in the end, stretches the retina.
How to determine the farsightedness or nearsightedness of
By the severity of the disease myopia and hyperopia is divided into three degrees:
Visual acuity is determined by special ophthalmologic tables. It is generally believed that with 100% vision, a person can clearly distinguish two points at a distance of 5 meters. The visual acuity is estimated at 1.0.When examining the vision using tables, a person from a distance of five meters is invited to name the letters located in several rows.
A person should read those letters in a row that he sees. The larger the letters a person sees, and the closer the distance to the table, the less the visual acuity. The erroneous name of several letters indicates an incomplete visual acuity. Each row in the table has its own meaning, which means visual acuity. The calculation is not only the distance from which the study is conducted, but also the distance that allows you to accurately identify all the letters in the series. When examining visual acuity, each eye is examined individually.
How to distinguish myopia from farsightedness according to the tables. As a rule, the 10 line in the tables for eye examination corresponds to 100% vision. In this case, the doctor will write OD = 1.0 and OS = 1.0 - this means that both eyes see the same and the visual acuity corresponds to 100%.If a person with one or both eyes sees smaller letters located on 11-12 lines, this already indicates hyperopia.
In the case of myopia, the subject can not name the 10th row of the table, and then find out which line he sees well. For a more accurate measurement it is necessary to use refractometers, which allow to determine the smallest deviations in vision.
With short-sightedness, visual acuity will be recorded with a value of "-", and with farsightedness "+".A weak degree of myopia includes visual acuity up to - 3.0 D( diopters), an average to -6.0, and a high degree of nearsightedness can reach -15.0-30.0.
Hyperopia is recorded as follows: weak degree to +2.0 D, medium to + 5.0 D and high degree from 5.0 D and above.