Presbyopia

Presbyopia (synonym age farsightedness) - the weakening of accommodation, developing people after 40-45 years. Presbyopia is caused by hardening of the lens and the loss of elastic properties. In this regard, the nearest point of clear vision is further away from the eyes, there are complaints about poor eyesight nearby (see accommodation of the eye). To correct presbyopia prescribe glasses with collective glasses. With age, the weakening of accommodation increases, in this connection it is necessary to increase the power of corrective glasses. In assigning points to correct presbyopia persons with emmetropic refraction (see refraction of the eye) can be guided by the table indicating the strength of the glass depending on age.
In the selection of such points in the case of myopia and hyperopia is taken into account their degree and are adjusted.

Age in years The strength of the glass in diopters
45-50
50-55
55-60
60-65 and more
1,0-1,5
1,5-2,0
2,0-2,5
2,5-3,0

Presbyopia (from the Greek. presbys - old man and opsis - vision) is a logical coming in old age physiological weakening of accommodation.
The elasticity of the crystalline lens with age due seal (sclerosing) lens fibers gradually decreases. Accordingly reduced ability to accommodation of the eye (see) and conditioned by it the ability to see clearly closely spaced objects. In individuals with normal refraction (emmetropia) presbyopia practically makes itself felt for the first time about the age of 40-45, when activities (reading, writing, etc.,) have visual fatigue phenomenon (the so-called accommodative asthenopia): the letters of the text are merged, there is a desire to push the subject of the studies further from the eyes (hence synonymous with presbyopia - old farsightedness). The reason is that long-term work at close range without the effects of visual fatigue is only possible when sufficient stock of accommodation, namely, when it is spent not more than half of the available capacity of accommodation, while the other half remains in reserve. If, for example, the subject of the studies is on average working distance from the eye to 33 cm, emmetrop must spend this 3,0 D ccomodation, that in these conditions to work without fatigue, it should have a total volume of accommodation not less than 6.0 D. These ratios are usually emmetrop at the age of about 40 years. At a later age emmetrop when you practice at a close distance is already required optical correction, i.e. the use of relevant points, compensating the resulting weakening of accommodation. For this purpose, are collectively (convex lenses that force which, of course, it is necessary to increase as further progressive weakening of accommodation. The approximate strength of the glass (d), requires persons with emmetropic refraction in different age shown in the table.
With farsightedness (see) the need to use glasses to practice occurs at an earlier age than if emmetropia; with myopia, on the contrary, in the later, with myopia over 3,0 D assigning points to practice may not be needed.
In practice in the appointment of glasses, correcting presbyopia, have to reckon not only with the age and the presence of one or another kind of eye refraction (see), but with the profession of the person, because the occupation is often requires a certain range, and what the distance is smaller, the more you want the glass and Vice versa. We also have to take into account the level of visual acuity (see), and in cases of significant down (what causes the need to approach the subject in practice to the eyes) to appoint a stronger glass, and sometimes even combine presbyopic magnifying glass with the system (see Points). In those cases when it is required at the same time correction and for Dali, and to practice, very useful to appoint bifocal glasses, the upper part of which is intended for Dali, and the bottom is near.