July 16, 2012 Presbyopia is the occurrence of weak vision at close range, which occurs between the ages of 40 and 45 when because of senile changes and loss of elasticity of the lens, accommodation strength of eyes weakens. Then the closest point of vision with the maximum of accommodation digresses from eyes for more than 33 cm.
Causes:
Presbyopia is the physiological phenomenon of ageing of the organism, especially of the lens. Already in youth, the lens gets a senile nucleus which after the age of 40 hardens. The harder the lens, the more it loses elasticity so it cannot bulge, nor can it increase the refractive strength when the ciliary muscle contracts and the zonular threads Zinis loosen. The occurrence of presbyopia depends on the width of accommodation with which the eye can adjust its dioptrical apparatus from the furthest point of vision (punetum remotum), when viewed without accommodation to the nearest point (punetum proximum), when viewed with a maximum accommodation.
Accommodation is the ability of the eye to see objects clearly at different distances, and in the range between the furthest and the nearest points of clear vision (punetum remotum i punetum proximum). The amplitude (perimeter) of accommodation is the strength of accommodation, expressed in diopters.
The amplitude of accommodation declines progressively with age, so in older age it reduces to zero. Between the ages of 40 and 45, the amplitude of accommodation greatly reduces and it is usually lower than 4, 00 diopters. Therefore, at persons whose work is consisted of reading, writing, or it is performed at a small distance, there are impediments occurring during work.
Symptoms:
When it comes to people whose work depends on precise vision at close range, the symptoms can appear very early. At those who do not use their vision for precise work at close range, the symptoms will appear later. They will experience difficulty while reading newspapers, or for example, while looking for a number in a phonebook. Vision “blurs”, letters “dance”, which can partly be compensated by moving away the book or the article that are being watched. Impediments are more expressed if the lighting is weak, especially at night when pupils are dilated. It is easier to read in the morning because the accommodation is better than at the end of the day.
Treatment:
Presbyopia is corrected by positive, convex lens collectors. The strength of corrective lenses is determined by the level of primary eye refraction, the width of accommodation, age and occupation. Distance from the object on which a person is working (working distance) is a very important factor for correcting presbyopia. The more delicate the job and the smaller the working distance – the stronger corrective glasses are required. The greater working distance and the harsher the job – the weaker glasses, for their optical value, are required.
Presbyopia is examined after determining visual acuity and refraction at a distance. With uncorrected hyperopia (farsightedness) presbyopia will occur even before the age of 40 and then for vicinity will be prescribed the strongest plus glasses with which the best visual acuity is achieved at a distance. After established diopter for distance correction, the one for proximity will be added. According to this, after the age of 45 hypermetropic presbyope, compared to emetrope (the one who has normal refraction), needs for vicinity that much stronger diopter of glasses as is his diopter strength for distance. That is why a hypermetrope will need to use two pairs of glasses after the age of 45; ones with weaker plus for distance, and others with stronger plus for vicinity.
Myopic (shortsighted) will own one pair of glasses for distance, which will correct their shortsightedness, and other pair – smaller minus for vicinity, according to age and working distance. At myopics of a smaller degree, presbyopic impediments occur later. For instance, at myopia of -2, 00 presbyopic impediments will occur only between the ages of 50 and 55, and until then this person will be able to read without eyeglasses.
At presbyopes with astigmatism in addition to corrective – toric glasses for distant vision, the ones also prescribed are sphero-cylindrical – toric glasses for vicinity, which correspond to the sum of the correction for distant vision and the value of presbyopia. When it comes to anisometropia, where one eye is farsighted, and the other one is shortsighted, when presbyopia occurs shortsighted eye can be used for working at vicinity, and farsighted eye can be used while looking into the distance. After the age of 55, old-age changes occur in the lens, sclerosis 4, 0 of the nucleus of the lens, therefore, the index of refraction in nucleus can increase, which leads to senile, gray reflex in the pupil and the appearance of old-age myopia. Then the strength of presbyopic glasses needs to be reduced. Senior myopia is a precursor of elderly cataract development.