What Are Bifocal Glasses?
Vision changes seem to be related to age. Presbyopia occurs in the middle age of one person, affecting your eye’s ability to focus. But it can be caused by bifocal glasses.
Bifocal glasses are divided into two parts to accommodate two different prescriptions in one lens. One area of the lens will have one prescription (usually distance) and a segment in the lower half will have the other (usually near vision).
Bifocal glasses were invented by Benjamin Franklin, who solved his own vision problem by taking the lens from his reading glasses and distance glasses and cutting them in half. Then remade the cut lenses into a single pair of bifocals and put the distance lens on top and the reading lens on the bottom.
However, the bifocal glasses come with some problems. So, in the following section, we will show you some common bifocal glasses problems.
The resurgence of celluloid glasses
However, in recent years, celluloid glasses have quietly returned to warm; It all started with a niche Japanese brand of handmade eyewear.
Most of Japan's top hand-made celluloid glasses are made in Mako Prefecture and are a favorite of many celebrities. Celluloid is a plasticizer with nitrocellulose as the main raw material. Cotton, pulp, and other fibers make up 70% of the raw material, which is mixed with camphor. Although the color is relatively limited, it has a unique material texture and texture, so Japanese handmade frame makers have been insisting on using it. Moreover, because celluloid is pretty stable when it dries, it can be shaped into a finer shape, keeping the frame intact even without metal leg cores.
What does vision insurance cover?
Vision insurance and vision benefit plans usually cover the cost of annual eye exams, prescription glasses, and/or contact lenses. Vision insurance includes traditional health/medical policies and health/discount plans that provide vision benefits and cover most. Coverage will vary depending on the type of vision insurance or vision benefit plan you choose. Group vision insurance is usually provided through an employer, an organization, or a government plan like Medicare or Medicaid. If you don't qualify for any of these options, you can purchase a personal vision care plan from a vision insurance provider.
Square-frame glasses
This frame is usually reserved for working women and can be paired with a simple or slightly sexy look, with tall eyebrows and dark lipstick. If they are big-frame glasses, usually they are more popular with some star friends. Big frame glasses collocate energetic dress-up, making a person unexpectedly full of sunshine and affinity.
Design principle of progressive multifocal lens
For the same piece of the lens, the top is used to see far, the bottom is used to see close. The upper and lower degrees are different.
There is not a sudden change in the distance degree fixed above the lens to the near degree fixed below the lens, but a gradual transition between the two through gradual changes in refractive power, which has special benefits over common bifocals or trifocal lenses.
How to choose rectangular glasses?
Look at the facial features in the aspect of proportion. If your features are delicate, which makes you look petite, you can choose some wider glasses so that you will increase your mental outlook, making your features prominent. On the other hand, if your features look solid and take up a large space of your face, go for narrower frames, because wider frames will make you look tired and add weight to your head.
The design evolution of progressive lenses
Spherical and aspheric designs
The design of the front surface of the far-use area of the early progressive lens is similar to that of the ordinary spherical single vision lenses, so it is called a spherical progressive lens. Since 1974, the front surface of the far-use region of the lens is designed to be aspheric by designers, which not only reduces the peripheral aberration but makes the lens thinner, lighter, and less powerful.
Hard and soft design
For hard design, the channel is short, and the gradient is large. The near-use area position is high. The effective visual area of remote and near-use areas was larger. Peripheral astigmatism is relatively concentrated. Because surrounding astigmatism increases rapidly and the distribution is dense, the curve effect is more obvious. The gradient area is narrow. It is more difficult and takes longer for wearers to adapt.
Lenses with soft designs have slower gradients, longer gradients, and wider gradients. The angle of rotation of the eye from the far area to the near area is greater. It's easier to get used to. Compared with the hard design, the effective visual area of the far and near use areas is smaller, and the location of the near use area is lower.
Single, diverse, and individualized design
Initially, the progressive lenses used a single design, in which each basic curve was scaled equally and a luminosity combination was added within the range of its semi-finished lens blanks. The steepest base curve uses the same lens design as the flattest base curve. Lenses designers quickly realized that the overall performance of the lens could be improved by microcustomizing the lens design, leading to progressive lenses with multiple designs. This kind of design is called diverse design. By the mid-1990s, there was the emergence of individualized lens designs. In addition to using different gradients, these first individualized lens designs used steeper baseline curves with a slightly larger approach area to compensate for increased magnification and reduced field of view.
Symmetrical and asymmetric design
There is no difference between the left and right eyes in the symmetrical design of progressive lenses. As the eyes turn inward when they see near objects, the gradual gradient area gradually tilts to the nasal side from top to bottom, so the left/right progressive lenses should be rotated clockwise/counterclockwise respectively during processing. An asymptotic lens with left and right eye divisions is called an asymmetric design. The gradient is gradually and moderately inclined to the nasal side from top to bottom. The refractive force, astigmatism, and vertical prism of the two sides of the left and right gradient of the asymmetric design lenses are basically similar. At the same time, considering the characteristics of eye movement parameters in binocular vision, the peripheral aberrations of the corresponding positions of the left and right lenses were appropriately balanced to improve the visual effect of the wearer.
