What are Bifocal Lenses, Intermediate-distance Lenses and Very-close Distance Lenses?

There are a number of types of spectacles (senior spectacles) available for the correction of presbyopia.The type introduced here is the [progressive lens].

This type of lens has no visible dividing line between the different prescription segments and enables the wearer to see objects in the distance, at close range and in the intermediate distance through a single lens. This type has become the mainstream senior lens.

Although no longer common, another type of lens is the [bifocal (trifocal) lens], a type with visible lines dividing the different prescription areas. Although, in terms of performance, this lens features a very wide range of vision for objects at close range, the eyes have to cross the dividing line between the different prescription areas to look at distant objects, impeding clear vision.In addition, since wearers of spectacles using this kind of lens can easily be identified as sufferers of presbyopia, this type is not very appealing in terms of appearance.

For these reasons, most people nowadays use the [progressive lens] for the correction of presbyopia.

Let's now move on to take a look at the various types of progressive lenses and points to bear in mind when selecting lenses.

 Types of Progressive Lenses

【1】Bifocal Type (Lens for normal daily use)

This is a very convenient type of lens that allows the wearer to focus on objects both at close range and in the distance through a single lens and eliminates the irksome need to frequently remove spectacles. This type of lens is designed to enable viewing of objects in the distance, at close range and in the intermediate distance with corresponding changes in power for each distance. Initially, these variations in power can, however, give the wearer uncomfortable feelings of swaying or distortion, or a sense of a narrow field of vision. (Almost all users quickly adapt and become accustomed to the variations in power.) Since these problematic sensations of swaying, distortion or narrow field of vision become more pronounced the greater the power of the lens, it is important to start using this type of lens from the 40's before the additional power (presbyopic power) becomes too great. Once the additional power increases to a certain degree, it may be difficult to become accustomed to the lens and the process of adjustment may take some time.

【2】Long-distance bias type (Ideal for driving)

This type of lens offers a wide field of forward vision and allows the user to see objects at close range without changing spectacles, making it the ideal choice for driving. This lens gives the wearer a wide range of long-distance vision and, at the same time, allows viewing of objects at close range such as meters, navigation screens and expressway tickets. This type can also be used for sports such as golf.

【3】Intermediate-distance bias type (For indoor and interior use)

Developed for indoor and interior use, this type of lens allows the wearer to view objects from a distance of about 3 - 4m ahead to objects at close range without removing the spectacles. Spectacles using this type of lens are, therefore, ideal for homemakers, for example, when watching TV, cleaning, cooking or reading. Moreover, this lens is also ideal for looking at whiteboards and documents at close range for example during meetings. When ordering an intermediate-distance bias pair of spectacles for the first time, we recommend that you actually try out a trial lens to ascertain "the range of vision this type allows and viewability" before proceeding with the purchase. Problems with viewability may gradually begin to manifest themselves if you do not first try out the lens before placing an order.

【4】Close-distance wide type ( For PC use)

Although this type of lens features less depth than the intermediate-distance bias type, it gives a wide field of close-range vision. This lens may be thought of as an intermediary type between the ordinary single vision lens for correction of presbyopia and the intermediate-distance lens. This type is ideal for people needing a wide field of close-range vision for desk work. For example, the ordinary single vision lens gives the wearer a field of vision of no more than about 30 cm ahead, and while this enables the wearer to see the keyboard when working on a computer, it may be difficult to see the monitor. The close-distance wide lens eliminates this problem, making it ideal for users working on computers.

 2. Points in choosing Progressive Lens

"Progressive lenses" can be selected to match specific purposes, greatly enhancing usability. Be sure to select the ideal lens to match to your needs - e.g. driving, eating and drinking or working with computers.

When consulting with your optometrist on lens selection, try giving accurate information such as the main situations in which you will be using the spectacles, what kind of range and field of vision you require and aspects of your current spectacles with which you are dissatisfied. No doubt, he/she will give you sound advice that will help you to select the ideal lens for your needs.