Criteria for Choosing Contact Lenses: "Consider Water Content and Oxygen Permeability"

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[Asia Economy Reporter Seo So-jeong] What criteria should be used when choosing contact lenses, a medical device worn on the cornea of the eye to correct vision?

The Ministry of Food and Drug Safety (Commissioner Kim Gang-lip) announced on the 12th that for wise purchase and use of contact lenses, one should consider the purpose of wear, wearing time, and living environment.

Contact lenses can be divided into 'hard contact lenses' and 'soft contact lenses' depending on the material. Hard contact lenses are made of hard materials such as glass or acrylic resin that do not absorb moisture, while soft contact lenses are made of materials with high moisture content and softness, such as hydrogel (hydrophilic polymer) and silicone hydrogel.

To obtain approval for contact lenses, all test and inspection items specified in the standard regulations, such as diameter, thickness, refractive power, ultraviolet and visible light transmittance, water content, oxygen permeability, eye irritation, cytotoxicity, and sterility tests, must be met.

Among the various test items for contact lenses, 'water content' and 'oxygen permeability' are closely related to the comfort and wearing time of the lenses. Water content, expressed as a percentage of the amount of moisture held by the contact lens, is measured only for soft contact lenses. This is because soft contact lenses are made of hydrogel or silicone hydrogel materials that can contain moisture within the lens itself.

Contact lenses with high water content are moist and comfortable to wear, but since they absorb moisture from the surroundings well, moisture evaporation is also fast, which can cause the eyes to dry out easily in dry environments.

Oxygen permeability refers to the rate at which oxygen passes through a unit area of the contact lens. Oxygen permeability varies depending on the characteristics of the contact lens material. The cornea of the eye has no blood vessels and receives oxygen from the external air and tears. Wearing contact lenses interferes with oxygen supply to the cornea, so oxygen permeability is related to eye health. If symptoms such as frequent eye redness or visible blood vessels occur while wearing contact lenses, it may indicate insufficient oxygen supply to the eyes, so contact lens use should be stopped immediately and an ophthalmologic examination should be conducted.

Soft contact lenses have high water content, resulting in less friction inside the eye when worn, providing good initial comfort and easy adaptation. They have less movement and foreign body sensation, making them suitable for people who engage in sports, leisure, and other active activities. However, their soft material makes them prone to tearing, and products with low oxygen permeability can cause redness and corneal edema with prolonged wear. The moisture absorption characteristic of the lenses themselves can also cause dry eye syndrome. Additionally, when engaging in water sports such as swimming, the risk of bacterial infection from contaminated external water may increase.

Hard contact lenses require time to adapt due to higher foreign body sensation compared to soft contact lenses, but once adapted, they can be worn comfortably for long periods. Generally, they allow better tear circulation and oxygen supply than soft contact lenses, reducing the likelihood of corneal or conjunctival diseases. However, there is a risk of lens displacement or loss during exercise.

According to the Ministry of Food and Drug Safety, as of August this year, a total of 723 products (591 manufactured by 60 companies and 132 imported by 19 companies) from 79 manufacturers and importers have been approved. On average, 500 million contact lenses are manufactured annually, with 64% (about 320 million) exported, and annual imports amount to about 140 million lenses.

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