Why does shape memory alloy have memory ability?
It starts with its microstructure. When a metal is solid, its atoms are always arranged in a regular way, forming a lattice. Under different conditions, such as temperature, metal may have a different structure, in which case it is said to be in a different phase. The change from one phase to another is called a phase transition. The properties of a metal change during a phase transition. The temperature at which a metal transforms is called the transition temperature. The difference between a shape memory alloy and other metals is that the phase transformation process in a shape memory alloy is reversible under certain conditions.
How To Use Contact Lens Correctly?
Check your eyes for abnormal cases. Do your eyes sting or dry? If so, it is recommended not to wear contact lenses for the time being. Look in the mirror to see both eyes carefully, if it is red and swollen or if is both eyes full of bloodshot? If you do, you can no longer wear contact lenses, and you can go to a professional store for inspection. After putting on the contact lenses, block the left and right eyes respectively to see if the vision of one eye is clear. If the eye vision has decreased or blurred, check if the lens is dirty. If the lens is still the same, you should go to a professional store to find out the reason.
The Price of Progressive Lens
On both sides of the lens of the progressive lens, some places are deformed, which makes the image blurred. In addition, it has a narrow field of view in the near and middle distances. The narrow focus point for a long time can easily make the eyes tired. It is suitable for the alternate vision of far, middle, and near. Under normal circumstances, the price of the progressive lens is different from the purchase merchant, region, brand, and quality, but the price of the progressive lens on the official website is between 30-85 US dollars. Of course, some products will be less than $30, or more than $85.
Service of GlassesUSA
Depending on your prescription, your glasses are possible to be delivered to your door within 10 to 20 business days. Glasses and contact lenses bought on the site come with a money-back warranty, free shipping, and return, and a 365-day warranty. GlassesUSA provides a two-for-one option. There are ready-made coupons.
The Pros and Cons of Shopping Glasses Online
Brick-and-mortar stores rely on a few or a dozen a day to make a profit, so the unit price is higher. Online stores have low costs. The profit can be made by volume, so the unit price is much lower. This is the advantage of online stores. The disadvantage of online stores is that it takes a lot of effort to get an optometrist, but optometrists have varying levels and attitudes. As a result, the prescriptions we get may not be entirely accurate. This can lead to uncomfortable glasses. The physical store glasses can try on. Choosing online glasses is not convenient.
3 Common Problems with Progressive Lenses
Though progressive lenses are popular to correct some eye conditions, there are also some drawbacks. So, in the following section, we will show you some common problems with progressive lenses.
Dizziness: the three different focal lengths of progressive lenses can make people susceptible to dizziness, as well as vertigo. From long to medium to short distance, the lenses offer a gradient of increasing strength. So, it would have trouble in adapting the glasses for the people who are wearing them for the first time. A common mistake is to look out of the wrong focal length, causing their vision to be blurry and lead to an overall feeling of dizziness.
Peripheral distortion: another common problem of progressive lenses is the way in which they blur peripheral vision. Most glasses cause an initial distortion to vision. However, the three different segments found in these lenses can make that distortion feel more prominent than other pairs of eyeglasses. And most people may need two weeks to adjust to progressive lenses.
Depth perception: Since progressive lenses provide three different prescriptions to see objects clearly for different distances, it is important that you need to move your head instead of your eyes when focusing on objects at different distances. Prior to adjusting to this little nuance, progressive lenses can cause depth perception to feel off.
From the above information, you have known some common problems with progressive lenses. So, you may ask how to adjust the progressive lenses. The most popular way is that you need to wear them frequently.
Why Do My Glasses Give Me a Headache?
Why do my glasses give me a headache? There are a lot of reasons for new glasses headaches. So, in this section, we will list some of them.
Muscle strain: each eye contains six muscles. Since your eyes learn how to view the world through a new prescription, these muscles have to work harder do differently than they did before. So, this action may cause muscle strain within the eye and a headache. If you are wearing glasses for the first time or if your prescription has changed significantly, you may be prone to this effect.
Multiple lens power: if you have changed to a multiple lens power of glasses like bifocal glasses, varifocal glasses, it may be difficult to adapt in a short time. So, this change will lead to some problems such as headaches.
Poorly fitted frames: as for the issue of new glasses headaches, if you glasses fit too snugly across your nose or cause pressure behind your ears, you may get a headache. So, when purchasing a new pair of glasses, selecting a fitted one is important.
Wrong prescription: why do my glasses give me a headache? It can be caused by the wrong prescription. If your eyeglasses prescription is too weak or too strong, your eyes will become strained causing headaches. So, if you still suffer from headaches after wearing the new glasses for a few days, contact your eye doctor and check the prescription again.