Closely associated with natural aging, presbyopia is a health condition where the eye suffers a progressively diminished ability to focus on near objects, explained by Wikipedia. A noticeable symptom of presbyopia is that those old individuals have to hold books or newspapers at a distance farther than the normal. Only with such a distance can they get a clear view. The exact cause of presbyopia is still uncertain. Some professionals claim the research evidence supporting a loss of elasticity of the crystalline lens. Meanwhile, there is still studying evidence showing that changes in the lens’s curvature have also been discovered. In fact, all these symptoms or causes are to some extent an inevitable result of natural aging. This also explains why most presbyopic patients are over 40 years old. Without proper treatment, presbyopia can be quite bothersome in daily lives. The presbyopic may have much inconvenience while conducting even small chores on a daily basis. When the condition is advanced enough, some patients resort to a laser eye surgery. But the simplest way is to use corrective eyeglasses. Until now, there are several types of prescription glasses for presbyopia: reading glasses, bifocal glasses, trifocal glasses as well as progressive reading glasses.
Reading glasses are the original version for presbyopia. With positive diopters only, reading glasses are capable enough of helping presbyopic individuals focus properly on near objects. These glasses come in single vision type only. Prescription of a pair of reading glasses should be determined by an eye doctor, in the same way as prescription glasses for other refractive errors. Even if reading glasses are available over the counter, it is advisable to purchase customized ones from eye care practitioners. However, a single pair of reading glasses is no longer capable enough if a person still has nearsightedness. Actually, such a combination is quite common in modern days. Many people suffer presbyopia after entering the 40s, before which nearsightedness has been existent for some years. Before the invention of bifocal glasses by Benjamin Franklin, this group of people had to use two separate pairs of prescription glasses, one for nearsightedness and the other for presbyopia. Fortunately, bifocal glasses in a single pair are designed to deal with these two problems at the same time.
There are even more advanced options for presbyopia. Trifocal glasses add a third power for computer vision to bifocal glasses. In this case, a trifocal lens has three vision zones in separate. Progressive reading glasses have a smooth gradient of powers, rather than several separated lens powers.