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Presbyopia is an age-related medical condition that leads to the loss of the ability to see objects clearly at a near distance. This gradual and progressive condition is as a result of lens hardening and accompanying decrease in length as well as strength of the ciliary muscle, which is responsible for the phenomenon of accommodation. Presbyopia mostly becomes evident around the fifth decade of life and almost everyone, regardless of how good their vision was throughout life, develops presbyopia at some point.
Those affected typically find themselves holding objects (e.g. a book or a phone) at distances further from their eyes than usual in order to see details on them more clearly. They may also complain of headaches, blurred vision and eye fatigue, which are worse in dimly lit environments or when feeling tired. Several tests, such as retinal examination as well as muscle integrity, slit-lamp, refraction, visual field and visual acuity tests are performed to diagnose presbyopia. It may then be treated in several different ways, such as with eye glasses, lenses and surgery. Surgery may be done to change the shape of the cornea, making near vision easier, or an artificial lens may be implanted after removal of the natural one.
Prime candidates for this mode of treatment are those who do not present with other problems that affect their vision. Reading glasses assist with the refraction of light before it enters the planes of the eyes. Persons who already use glasses due to a preexisting problem may need a new set of glasses depending on their condition. The purpose of bifocal glasses is to correct both near and far distance problems. With these spectacles, the lens has two parts, where the lower half of the lens may be used for near vision and the upper half for far vision.
In contrast to bifocals, there are trifocals and progressive lenses. Trifocal glasses have three areas within the lens that allow for far, near and mid-range vision. Likewise, progressive lenses are different from bifocals in that they have a gradual change in dioptric power from the upper and lower halves of the lens to correcting vision from the far to near point. This avoids the abrupt change at the visible delineating border that one may note with bifocal lenses.
Contact lenses are the preferred choice in persons who, for many reasons, such as convenience or aesthetics, do not want to use eyeglasses. For presbyopia, the two main types of contact lenses used are mono-vision and multifocal contacts. Mono-vision contact lenses work by correcting one eye for near vision and the other eye for far distance. These lenses require some time for adaptation and persons often complain that these lenses cause a loss in one’s ability to judge the speed or distance of moving objects.
Multifocal contact lenses possess the property of several zones within each lens that is preset at different optical powers. This allows for a person to be able to use both far and near vision simultaneously. It takes some time, however, as the brain learns to adapt to the new artificial arrangement. Moreover, these lenses offer inferior visual acuity in comparison to their mono-vision counterparts.