OK lens, short for orthokeratology, is actually a kind of contact lens.

Contact lenses can be roughly divided into hard contact lenses and soft contact lenses according to different materials.

Soft lenses, as we all know, are the contact lenses we talk about every day, mostly made of hydrogel. The lens is soft and comfortable to wear, but the disadvantage is that the lens has poor formability.

Hard lens, now mainly refers to high oxygen permeability hard contact lens (RGP), which has high oxygen permeability and good lens formability, but the lens is hard, and it takes some time to get used to it for the first time.

OK mirror belongs to hard mirror, but it is different from general RGP. Ordinary RGP is mainly worn during the day, while OK glasses are worn at night to correct vision by changing corneal morphology, and glasses are not needed during the day. However, the effect of OK glasses is reversible. If you stop wearing it for a while, the degree will change back. So in order to maintain that you don't need to wear glasses during the day, you need to wear OK glasses at night.

How can a mirror correct vision?

OK mirror is different from ordinary RGP, except for the different wearing time. The main difference lies in the lens design. As we all know, the lens has two surfaces, one is the inner surface attached to the cornea, and the other is the outer surface in contact with the eyelid.

Generally, the inner surface of RGP is parallel to the cornea, and the vision can be corrected by changing the outer surface to adjust the lens power. On the other hand, the outer surface of OK mirror is relatively simple, but by designing the inner surface in reverse geometry, the effect of corneal shaping can be achieved.

At present, most of the OK mirrors used in clinic are divided into four arc areas, namely, basal arc area, inverted arc area, positioning arc area and peripheral arc area.

The basal arc area (also known as the central optical area or treatment area) and the anti-arc area are responsible for keratoplasty; The positioning arc area is responsible for lens positioning, and the peripheral arc area is responsible for tear exchange.

Figure: Schematic diagram of OK mirror lens design

Wear OK glasses at night, and your eyes will still blink when you sleep, that is, blink. Every blink of an eye will produce a pressure on the OK lens, which will be transferred from the basal arc of the lens to the cornea, forming a positive pressure on the central cornea.

However, the convex anti-arc area forms a negative pressure similar to siphon on the cornea, thus producing traction. At the same time, the tears between the cornea and the lens will flow along the pressure difference between the base arc area and the reverse arc area, generating a force to make the cornea and the lens suck more and more tightly, thus completing the shaping of the cornea and achieving the purpose of correcting vision.

Therefore, everyone's OK glasses need to be customized according to their corneal morphology and myopia.

What kind of people can wear OK glasses?

The general fitting range is within 600 degrees of myopia and 200 degrees of regular astigmatism, which is more suitable for myopia < 450 degrees and regular astigmatism < 150 degrees. Regular recommended fitting age is over 9 years old.

Even if the above conditions are met, not everyone can wear OK glasses. Check your eyes carefully first to see if you can wear them. If there are problems such as poor corneal condition, active conjunctival inflammation, obvious dry eye symptoms and high intraocular pressure, it is not recommended to wear it.

Moreover, because of the high price of OK glasses, a pair of OK glasses may be made in China for thousands, and imported for more than 65,438+10,000. If well maintained, it can only be worn for about two years. Plus the cost of nursing solution and reexamination, the average cost is tens of thousands a year, so the cost of this piece also needs to be taken into account.

For adults, this cost can basically be used for myopia laser surgery, so few adults choose this way to correct their vision. For children, because OK mirror can control the development of myopia to a certain extent, it is mainly used by teenagers in clinic at present.