Buying the wrong contact lenses can damage your cornea! Many people don't know these indicators that you must look at.

Nowadays, many people choose to wear contact lenses, which not only provide clear vision for the wearer, but also free them from the constraints of frame glasses. Nowadays, many girls use colored contact lenses as a must-have item for beauty.

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However, if they are not selected or used properly, they may cause a series of eye problems for the wearer.

For example, the product you buy has low oxygen permeability, which may cause the wearer to suffer from corneal hypoxia. In mild cases, it may cause eye discomfort and red bloodshot eyes. In severe cases, it may cause corneal neovascularization, leaving irreversible damage.

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Or the wearer may have abnormal tear secretion and buy the product without checking, mistakenly believing that the higher the water content, the more hydrating the eyes are. As a result, the more they wear the glasses, the drier their eyes become, and they may even have difficulty taking them off.

It can be seen that the correct selection and use of contact lenses can ensure the safety of wearing and make beauty and health coexist. Next, let's talk about how to choose contact lenses correctly~

Good contact lenses have 5 characteristics

First of all, a pair of high-quality contact lenses should have the following characteristics:

① Comfortable to wear. No foreign body sensation or irritation when wearing, smooth surface and reasonable edge design.

② Clear vision. Good correction effect, good optical properties of materials, and accurate refraction.

③Good oxygen permeability. Long-term wearing will not cause discomfort or complications due to oxygen metabolism disorders.

④ Non-toxic. The material is completely polymerized, and the additives and care ingredients do not cause toxic reactions to human eye tissue cells.

⑤Good formability. The lens is easy to put on and take off.

Of course, these characteristics are the result of combining the user's subjective experience. Products that want to meet the above points need to be supported by corresponding product parameters.

Three principles for choosing a lens

If you find it difficult to understand the many parameters and indicators when choosing contact lenses, then remembering these three principles of lens selection can help you quickly choose the right product.

Three principles for lens selection

1. Choose well-known brands

The preference for well-known brands is not only a pursuit of product quality and safety, but also based on the fact that these brands usually have more stringent quality control processes, more complete customer service systems and strong product research and development capabilities.

Well-known companies are often willing to invest a lot of resources to ensure the safety and comfort of their contact lens products, strictly follow domestic and international market standards, and conduct detailed clinical tests before launching their products to market.

In addition, big brands have more users and can better identify potential problems. Even if adverse medical device events occur, they can be tracked in a timely manner and potential risk products can be recalled to prevent the problem from further expanding.

2. High oxygen permeability material

Because the cornea's oxygen absorption level is crucial to maintaining corneal health, most of the oxygen needed by the cornea comes from the outside air and the blood vessels of the eyelid conjunctiva.

Therefore, wearing contact lenses will inevitably hinder the cornea's oxygen intake to a certain extent. The oxygen permeability of contact lenses is one of the core keys to healthy wearing.

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So how do we judge the cornea's oxygen supply needs?

The physiological edema of the cornea after we sleep causes the cornea to thicken by 4%. Through experiments on wearing contact lenses with different oxygen permeabilities, it was found that when the oxygen permeability of the lens reaches 24DK/t, corneal edema is close to the physiological edema level. Therefore, the minimum oxygen permeability requirement for safe daily contact lens wear should be 24DK/t to ensure the safety of the cornea.

Once the oxygen permeability is too low, it may cause a series of changes in corneal morphology, including epithelial cell reduction, epithelial microbubbles, epithelial microcysts, epithelial peeling, corneal edema, and even corneal neovascularization.

Note: Corneal neovascularization is irreversible and will spread along the edge of the cornea toward the center of the pupil. After atrophy, it will leave a tree-like structure that will affect vision for life.

The hydrogel materials that were once more commonly used need to increase the water content of the lens to improve the oxygen permeability of the lens. This can also affect the wearer's eye comfort due to the excessive water content of the lens. When the water in the lens evaporates, it will absorb tears to replenish itself, causing the wearer to experience dry eyes. Even with a higher water content, the increase in oxygen permeability is still a drop in the bucket and can only meet the basic oxygen permeability needs of the cornea.

The new silicone hydrogel material is a highly oxygen permeable material, and through continuous updates, comfort is now guaranteed, and it is widely considered to be the best choice for contact lens materials. Studies have shown that contact lenses made of highly oxygen permeable materials can significantly reduce the risk of corneal hypoxia.

3. Short-cycle products

Contact lenses can be roughly classified according to the product's usage cycle as shown in the table.

In the early days, people believed that contact lenses could be used forever until the lens broke or the deposits became so much that they affected vision and needed to be replaced.

However, with the continuous deepening of research and the improvement of awareness of the hazards of lens surface deposits, the current view is that the use cycle of lenses should be gradually shortened. This can not only improve the wearing comfort of lenses, but also minimize various eye complications caused by lens deposits. In other words, the shorter the use cycle, the healthier it is.

Therefore, combining the above three simple lens selection principles, the best combination is a short-cycle product made of silicone hydrogel from a big brand. From the perspective of optimal use, daily silicone hydrogel lenses are definitely the most user-friendly and safe, but at the same time, the price will be slightly higher. If you want the most cost-effective combination, then you must choose monthly silicone hydrogel lenses, which have high oxygen permeability, adequate care and safety, and are more affordable.

Develop good habits of wearing contact lenses

Of course, even if the product is chosen correctly, it can still cause some eye health problems if it is not used correctly.

① Some people choose short-term monthly disposable products, but do not use them according to the usage cycle. They think that they have not worn them for 30 days after opening them for more than a month, and choose to continue using them. Some people think that daily disposables are too wasteful and wear them repeatedly. These methods are likely to cause eye infections.

② In addition, some bad habits, such as wearing lenses to sleep, overnight or even for many days without taking them off, can lead to eye infection at the very least, and can cause adhesion between the cornea and the lens at the worst, making it impossible to remove the lenses smoothly.

Therefore, if you want to use contact lenses healthily and safely, you not only need to choose the right products, but also have the correct wearing and care habits.

Finally, I wish you all a healthy, comfortable, long-lasting and safe wearing of glasses.

References

[1] Xie Peiying. New technologies and advances in soft corneal contact lenses[M]. Peking University Medical Press, 2020.

Corzine,John.ClinicalManualofContactLenses,4thed.EdwardBennettandVinitaHenry[J].Optometry&VisionScience,2014,91(4):e95.

[2] Xie Peiying. Contact lens fitting technology[M]. People's Medical Publishing House, 2012.

[3] Qi Bei. Corneal contact lens[J]. People's Medical Publishing House, 2014.

[4] Qi Bei. Corneal contact lens[J]. People's Medical Publishing House, 2014.

[5] Lü Fan. Contact Lens Science[M]. People's Medical Publishing House, 2011.

[6] Chen Zhi, Zhou Xingtao. Interpretation of the 2017 edition of the American Society of Ophthalmology Clinical Practice Guidelines (PPP): Safe and Expanded Application of Contact Lenses[J]. Chinese Journal of Ophthalmology, Otolaryngology, 2019, 19(6): 2.

[7] Johnson & Johnson Acuvue Advisory Expert Group. White Paper on Eye Health Related Content of Soft Contact Lenses - Consensus of Ophthalmologists (2017 Hangzhou, China Conference). Johnson & Johnson Acuvue Advisory Expert Group. Chinese Journal of Optometry and Visual Science, 2018, 20(6):321-325.

[8] Zheng Rongling, Zhong Fuling, Zhang Qinfan, et al. Clinical analysis of contact lens-related corneal neovascularization. Ophthalmic Research, 2000, 18(2):157-159.

Author: Jin Xin, Director of the Shouyang Myopia, Strabismus and Amblyopia Prevention and Control Research Institute, Huainan City

Review丨You Yuxia, deputy chief physician, Beijing Aier Xinli Ophthalmology, doctor of medicine