What Is Progressive Lens?
Progressive lenses, also called multifocal lenses, have three prescriptions in one pair of glasses. So, it allows you to see near, middle distance, and far objects without changing your glasses. The progressive lenses are designed for people who are over 40 years old who are both nearsighted and farsighted. The progressive lenses come with the following features:
- There is no distinct line between all visions(near, intermediate, and far).
- Most popular lens for anyone with presbyopia who wears
- Expanded intermediate zone for better computer vision.
From the above information, you may have known the differences between bifocal lenses and progressive lenses. As for progressive vs bifocal lenses, which one is better? It is difficult to judge because each of them has unique features. So, if you do not know choose which, you can listen to the eye doctor.
How do you identify the refractive index of lens?
In reality, this problem is often a problem for optical shop practitioners, sometimes they worry about whether the manufacturer's lenses match the nominal value of the refractive index. We need a prop, and that's the camber. Because it can be used to measure the strength of the lens. The luminosity of the lens can be calculated by subtracting the curvature of the inner and outer surfaces of the lens. The curvature difference of a lens of the same luminosity is inversely proportional to the refractive index, that is, a lens with a higher refractive index only needs a smaller curvature difference to achieve the same luminosity.
Optometry glasses are not professional
Some people will not only experience dizziness when they change their glasses but also have headaches, nausea, vomiting, inattention, neurasthenia, and other symptoms from time to time. And some people even deepen myopia. This is most likely due to unqualified glasses and inaccurate optometry. In short, this eye discomfort is caused by the inconsistency between the power of the glasses and the actual condition of the eyes. Optometry before filling a prescription is a very important step. In addition to checking myopia and astigmatism, it is also necessary to check for eye disease, binocular vision balance, monocular ability, primary vision discrimination, interpupillary distance, etc. In this way, suitable glasses can be fitted according to the overall situation of the person's eyes. The spectacles must also match the parameters of vertex, interpupillary distance, cylindrical lens axis position, etc. Otherwise, it will directly affect the effect of correcting vision, cause the user's visual fatigue, and increase the emphasis on power loss.
Why should you clean the eyeglass case?
Although the eyeglasses case is used less, it can not be separated from the glasses. If it is not cleaned for a long time, it will affect appearance and carry a lot of bacteria.
Figure out the categories of driving glasses
Driving glasses are usually divided into daily and night glasses. Daily use refers to the glasses with anti-glare function and darker colors like gray, brown and gray-green, and other colors. Daily lens transmittance is over 8%. Night type usually refers to the glasses that can prevent glare from headlights of opposite vehicles and increase brightness at the same time. That is, it can prevent lights and not block the road, and can brighten and increase the visual scope. Night lenses have a transmittance of more than 75%.
Ray-Ban Wayfarer Ease Optics
Perhaps the most famous square glasses on the market are the Ray-ban hikers. These glasses add a classic, cool style to your look. If the line is thick, select black. If you have a lot of colors, go for Havana red. Similar to rectangular glasses, square glasses are best for round or oval faces.
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.
