Refractive index of spectacle lens
It is generally believed that the higher the refractive index, the better the spectacle lens. Such spectacle lenses are relatively thin, and of course, the price is a bit expensive. When the refractive index increases, the direction of the light entering the lens will change greatly, the focus will move to the lens, the focal length will be smaller, and the diopter will become larger. In order to keep the diopter unchanged, it is necessary to reduce the curvature of the lens, that is, to reduce the curvature of the mirror surface, so that the thickness of the lens can be reduced. This is why the larger the refractive index, the thinner the lens is. Under the same premise of other things, the larger the refractive index, the thinner the lens, the lighter and more beautiful the lens, and the higher the price, but the larger the refractive index is not the better.
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Reduce the amount of time you spend using electronics.
When children are developing their eyes, parents should limit the amount of time they spend with electronic devices. Increase outdoor exercise and combine work and rest. In today's high-pressure and competitive learning environment, children face textbooks, homework, and exams for a long time, and their eyes do not get a good rest. Outdoor sports can effectively relax children's eyes, reduce children's visual fatigue, but also be more conducive to the healthy development of children's bodies and minds.
Do night driving glasses really work?
Yellow lenses reduce the amount of light entering your eye, reducing visibility. These darker colors block more blue light than yellow lenses. But they block more light from entering the eye, reducing visibility even more in low-light conditions. In fact, even yellow lenses reduce overall visible light to some extent because they block some blue light. This can be a good thing during the day, but not at night, when maximum visibility is key. Night driving glasses come in a variety of yellow and amber colors. The darkest lenses filter out the harshest light, but they filter out the largest amount of light, making it difficult to see in dim or dark conditions. Some people who wear night driving glasses say they can see better with them on. However, vision tests have shown that night driving glasses do not improve night vision, nor do they help drivers see pedestrians any faster than they would without glasses.
Why is a prescription for glasses different from a prescription for contact lenses?
The frame glasses degrees are the optometric degrees of the eye, and the difference between the frame glasses degrees and the contact lens degrees is mainly due to the different contact distances between the two lenses and the eye. Usually, degrees of contact lenses and glasses need to be converted by a professional through vertex diopter. The conversion formula is Fc=Fs/(1-d×Fs). In the formula, Fc is the diopter of contact lens, Fs is the diopter of glasses frame lens, and D is the distance between frame glasses lens and cornea. Assuming that the prescription of frame glasses is -4.00d and the distance between lens apex is 12mm, the prescription of contact lenses is -4.00/ [1-0.012×(-4.00)] = -3.82d.
Type of eyeglasses cloth
There are many kinds of cloth for glasses. There is mainly sheepskin eyewear cloth, and there is microfiber eyewear cloth. There are suede and double-sided cloth and so on. Professional eyewear cloth must use more than 200 grams of weight/per cubic centimeter of microfiber. This kind of raw material chemical fiber is fine, and tactility is soft, so it will not damage the lens. This kind of wipe cloth can be used on a computer screen. The two sides of the cloth are different, and the smooth side is used to scrub the lenses. Because the dirt on the lens is mostly small. The rough side is designed to give you more friction when you touch it with your finger, so you can use it more easily, and you can clean it more.
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.
