I’m 41 and my optometrist told me I need bifocals. I don’t want the old-fashioned ones with the lines.
For most people, when we reach close to 40 years of age, we lose the ability to focus up close although the distance vision remains the same. We now need additional power to see near. Since most of the near work is done below eye level (reading, working at a desk, sewing, etc), the additional power is placed in the lower portion of the spectacle lens and usually set in focus at about 40-50 cm. The first bifocals were developed in 1784 by Benjamin Franklin, where the reading portion of the lens went all across the bottom of the lens. This type of lens was called an ‘executive’ bifocal
The disadvantage of this type of lens is that the whole bottom field of vision was blurry and only in focus at 40-50 cm. A more popular shape emerged where the add is now a semicircle (D) shape.
When we read, our eyes turn inward, so the D segment is placed towards the nasal portion of the lens. This allows the viewer to still see distance objects through the lower outer portion of the lens. These bifocals all have visible lines where the near portion is located. Progressive bifocals have the power ground into the lens and there are no visible lines.
What are progressive
lenses?
These are another name for invisible, varifocal, or no-line bifocals. These lenses are more expensive than regular bifocals. They are manufactured in such a way as to move smoothly from distance to intermediate to near vision.
There are two main downsides to this type of bifocal. Because the powers are blended centrally, vision through the sides of the lenses is not clear, with slight distortions that increase with stronger prescriptions. Also, the near area is smaller and in a specific spot on the lens – 15-20 mm below the distance area, so you have to learn where that area is and look through it to get the best near vision.
These lenses come pre-made with the distance and reading portion in very specific parts of the lens. As such, they have to be fitted into a frame where both the distance and near portions can be accommodated. As a result, these lenses cannot be fitted into very small frames as they will cut out either part of the distance or near portion.
