For girls who love beauty, wearing glasses for myopia is really a big worry. Not only will this greatly compromise your beautiful makeup, but it is also a big burden when taking photos. It is impossible to take photos of your face wearing glasses. Satisfied photos. Therefore, contact lenses have become a good choice for people who love myopia/hyperopia/astigmatism. But how can you choose the contact lenses that suit you? Now let’s take a look at one of the essential knowledge for purchasing contact lenses at 818 – the parameters of contact lenses.
There are six main parameters for contact lenses: replacement cycle, water content, oxygen permeability, base arc, diameter and center thickness.
Before introducing each parameter, let’s briefly introduce the main contact lens materials currently on the market. At present, contact lens materials are generally divided into traditional hydrogel and silicone hydrogel. Traditional hydrogel materials require water to transmit oxygen, but silicone hydrogel materials add silicon. Silicon can increase the conduction of oxygen, so it can no longer rely solely on water to conduct oxygen. Silicone hydrogel material can conduct oxygen through silicon and water together, so its oxygen permeability is much higher than traditional hydrogel. Of course, the price of silicone hydrogel contact lenses is much higher than traditional hydrogel. To sum up: Silicone hydrogel materials are better, and silicone hydrogel contact lenses are generally short-cycle disposable contact lenses.
1. Replacement cycle
According to different replacement cycles, contact lenses can be divided into two categories: traditional lenses and short-cycle disposable lenses. Traditional lenses refer to replacement cycles of more than three months, such as quarterly and annual lenses. Short-cycle disposable lenses refer to replacement cycles of less than three months, including monthly, two-week and daily disposables.
When Juny was in college, she always purchased annual disposable contact lenses. The specific brand should be Okra, and the price was around 200-300. At that time, I felt that annual disposable contact lenses cost two to three hundred, while monthly disposable contact lenses only cost tens to more than a hundred. Based on the principle that the more expensive the better, annual disposable contact lenses should be better than monthly disposable ones. Until 2015, I was chatting with a Korean friend about contact lenses.
She took out a box of small things and said that she wore this one and could wear it all day long. When I came back and checked, I found out that these are two-week disposable contact lenses (Ouscomm two-week disposable), and I also learned that contact lenses are still disposable in two weeks! I tried wearing the Johnson & Johnson O-Comfort for two weeks, and then I felt that the annual disposable I wore before was really abusing my eyes! !
Nowadays, quarterly and annual disposable contact lenses have been gradually replaced by short-cycle contact lenses. At least in developed countries, quarterly and annual disposable contact lenses are almost no longer sold. The shorter the replacement cycle, the more comfortable and healthy it is, but the cost is also higher. Changing new lenses every day will definitely have a different level of comfort than changing lenses once a month or half a year.
2. Moisture content
The water content should be more accurately called “water absorption”. The higher the water absorption, the more water the lens needs, and the easier it is to cause dry eyes. The water content of invisible silicone hydrogel is generally not higher than 50%, and the moisture content is good. But for traditional hydrogel invisibility, since it relies on water to transmit oxygen, it needs to increase the water content to increase oxygen permeability. Therefore, the water content of traditional hydrogels is generally above 50%, and the moisture content is obvious. Not as invisible as silicone hydrogel material .
3. Oxygen permeability
Oxygen permeability refers to the amount of oxygen that the lens allows to pass through per unit time. The international unit is Dk/t. Generally speaking, when the oxygen permeability is >=20Dk/t, it is considered qualified and can be worn daily, but the wearing time is best not to exceed 8 hours. When oxygen permeability = 25Dk/t, 80% of oxygen can pass through. This type of invisibility can theoretically be worn for up to 10 hours a day. When the oxygen permeability is >=125Dk/t, you can theoretically wear contact lenses overnight, but it is strongly not recommended . Unless there are special circumstances, do not wear contact lenses overnight. The higher the oxygen permeability, the healthier it is for the cornea and can also reduce red blood filaments caused by corneal hypoxia.
The oxygen permeability is affected by its own material. As mentioned above, the invisible oxygen permeability of silicone hydrogel material is better than that of traditional hydrogel material . This “good” is not just a little bit better, it’s better in magnitude. The invisible oxygen permeability of traditional materials is more than 20, more than 30, and may reach more than 80 in some cases. The invisible oxygen permeability of silicone hydrogel materials starts at 100, and the difference is obvious. In fact, there are currently only two types of invisible products that can be wear for more than 10 hours without any foreign body sensation or dryness: Dailies Total 1 and Oasys 1-Day.
4. Base arc
The base curve refers to the degree of curvature of the lens. The larger the base curve, the smaller the curvature. The closer it is to a plane, the flatter the eyeball is. On the contrary, the smaller the base curve, the more convex the eyeball is. The average person’s base arc is between 8.4 and 9.0. The size of the base arc needs to be calculated by going to an optical shop and having an optometrist take an exam. Under normal circumstances, a person’s base curve will not change, so you can write down your own base curve after going to an optical shop for an optometry test, so that you can choose the model that suits you when purchasing invisible lenses in the future.
Most people’s base arcs are around 8.6, and most invisible base arcs are also around 8.6. If the measured base arc is 8.4 or 9.0, then it is recommended to wear 8.4 or 9.0. If it is 8.6, you can try 8.5-8.8. Many people don’t feel the difference between wearing 8.4 and 8.8, but some people feel there is a slight difference, so the best way is to give it a try .
5. Diameter
The diameter of contact lenses is generally around 14.00mm-14.3mm, and the diameter of astigmatism contact lenses will be relatively larger, around 14.5mm.
6. Center thickness
The center thickness of contact lenses, even for products of the same model, will change with changes in power. Center thickness listed by the manufacturer generally takes 300 degrees of myopia as an example. The center thickness is <=0.05mm, which is ultra-thin; =0.07mm, which is standard; >0.07mm, there is no general name. The center thickness is generally within 0.10mm, and there will not be a big difference in comfort.
The above are several parameters that can be consider when choosing contact lenses. As for eye power, it varies from person to person and is not includ in the contact lenses. It should be note that the parameters are only a reference when purchasing. They are to allow you to better understand the basic situation of the invisible device you purchase. Which invisible device you choose will ultimately depend on your wearing needs for invisible products and your purchase budget. But one thing is very clear, and it has been said many times in the article, silicone hydrogel contact lenses are better!
