Hypermetropia

The parallel rays coming from infinity are diverted (refracted) from the system cornea/crystalline on a specific portion of the retina that allows the sharp vision: the macula. So an eye that can perfectly converge parallel rays coming from infinity on the macula is an eye emmetropic. In this eye has gone a harmonious and balanced development of its size and its "Refractive system" (Cornea / lens). In this eye has gone a harmonious and balanced development between its anteroposterior and its refractive system that is, the cornea and lens. In Italy, by custom, an emmetropic eye has a’visual acuity (or visual acuity) of 10/10 (ten / tenths) (Snellen fraction). They are often confused the tenths of this fraction, then how many lines that express the law on patient’ottotipo (the table using the ophthalmologists) out of a total of 10 (then the patient will read; 1/10; 2/10 and so on up to 10/10 for the smallest letters) with diopters (improperly degrees) that are, the unit of measure of the power of the lenses (positive, negative or cylindrical) necessary to correct a particular defect of refraction . (For example, a slight myopic needs an eyewear - 2 diopters to see the 10/10 otherwise your eyesight without glasses would be below 1/10). At birth all have an eyeball shorter than the standard (farsighted). Development in the period following, unlike its front part (cornea and crystalline reaching already 2 years, the normal size) is mainly dependent on its rear portion of the rapidly growing (probably influenced not only by genetic factors as well as environmental factors and neurological) taking the size of the adult (about 23,5 mm in a normal subject) adolescence. If during this development, the eye becomes longer than expected realized an imbalance between the cornea-lens and axial length of the eye and is called myopic and the rays are focused in front of the retina. If the eye, at the end of its growth, "Remains" shorter than expected realized, Also in this case, an imbalance between the cornea and lens-axial length. In this eye parallel rays coming from infinity instead of the macula, will be in focus behind the macula and on this are formed of the images even more blurred the greater is the imbalance between the two systems (ie the higher hyperopia). That lack refractive, opposite to myopia, defines hypermetropia. A difference of myopia, however,, nature has made available a system which is what we use to see close up, to compensate, at least in part, that defect refractive: the accommodation. A change in the power of the lens can compensate for this defect it up to be able to clearly see the 10/10 while having hypermetropia of 1-2 diopters (and young people more) without apparent effort. To close, however, appear, especially in the long-term vision and in relation to age, symptoms of tiredness and fatigue (mist, splitting of the image, etc,symptoms that define accommodative asthenopia). It’ why it is appropriate to make an eye examination with cycloplegia, especially for children, where the defect can be misunderstood and often responsible, in early childhood, the strabismus. Hyperopia is corrected with converging lenses (or positive) which are able to bring the focus exactly on the macula, with contact lenses or through the correction surgery (refractive surgery).