EYEGLASSES LENS STYLES
Talk to our Optometrist and optical team about what you are going to be wearing your eyeglasses for and what style of lens you are going to need for your prescription. Some people need just single vision and others need multifocal/bifocal lenses in order to see optimally at any distance. Here is in overview of the main types of lenses you can get at our office in Bellingham.
SINGLE VISION LENSES
Single vision lenses have one prescription only in your lens. Your eye doctor might specify that you need to wear them full time, just some of the time or for certain activities or distances, like driving only or reading only. The advantage of single vision lenses is often that they provide a fairly uniform viewing experience across the entire lens.
Bifocal lenses have two prescriptions strengths inside each lens. The prescription for the distant objects (those 20 feet away or farther) is almost always at the top of the lens, and the prescription on the bottom is used to focus near objects at arm's length. The types of bifocals are as follows:
Flat Top 28: The near prescription extends 28 mm across the lens.
Flat Top 35: The near prescription extends 35 mm across the lens.
Executive: The near prescription of the lens extends across the whole lens.
Round Segment: The near prescription is a circular area at the bottom of the lens rather than a flat top.
Trifocals are lenses with three sections, each with a different prescription. Like bifocals, a line will serve to mark the separation between each segment. The top section is for distance, the middle is for focusing on objects from 2-4 feet and the bottom section is for focusing on reading.
The progressive lens market began in 1959 with the Varilux lens and it's improved ever since. Most patients who need a different strength prescription power for distance and near end up choosing progressives over their other options which inlude bifocals, trifocals and separate pairs of glasses for each viewing distance.
Though they've become the popular choice for most people with multi focal needs, they are not completely without flaws. You might even have friends and family members telling you not to try progressives or that they "can't get used to progressives."
HOW PROGRESSIVES ARE MADE
Contrary to popular belief, progressive lenses are not "no-line bifocals". They have their own technology and manufacturing process which is separate from bifocals and trifocals.
Progressive lenses have specific curves added to the front surface of the lens which gradually increases the near (plus) power from the distance (top) portion of the lens down to the near (bottom) section. Many progressives now use these curved surfaces on the back of the lens for added optical quality.
For most progressive lenses, the distance prescription correction should be located at the optical center/midpoint of the lens and upward. The near prescription in the lens is generally found about 10 to 18 mm below and 2 mm inward from the center.
Progressives can be made with either a "hard design" or a "soft design." A hard design refers to a more distinct transition from the distance and near. This will be easier to get used to for those who are accustomed to lined bifocals. In a softer design, the transition from distance to near is less obvious and will generally include a larger area for intermediate (in between) vision correction.
WHAT ARE THE PROS AND CONS OF PROGRESSIVE LENSES?
No distracting line through the lens
Optimal vision correction (possible) at any distance
No sudden change in lens power or "jump" in image location like in bifocals/trifocals
Straight lines might look curved
Viewing area is reduced in the intermediate and near portions of the lenses.
Requires some head and/or chin movement in order to find the "sweet spot" in the lens
Those who get motion sick, or are more prone to balance problems don't adapt as well to progressives (although a "soft design" can minimize these problems).
Aside from those attributes, progressives will often vary based on brand and prescription powers.