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In 1960, it was invented by Otto Wichterle using a "hydrogel" material, which was called and used hydrophilic plastic in many medical fields.
It is a lens that can be contacted without damaging the lens by bending both ends of the lens. Soft lens is made of HEMA (Hydroxyethyl methacrylate) and added a small amount of various monomers, so it is soft and comfortable to wear. Currently, silicone hydrogel lenses have been developed that improve low oxygen permeability, which is a disadvantage of conventional hydrogel lenses.
Type of Soft Lens
Daily Wear Lens: The most common soft lens, worn in the morning and removed in the evening. Lens life is usually about 6 months to 1 year.
Continuous wear lens: This lens is made of a material that can be worn when sleeping. It is allowed to be used without removing from eyes for 7 days to 1 month.
Although it is possible to receive complications, care must be taken when wearing it continuously.
1) One-day Soft Lens: This lens is discarded after one day of use. It is convenient to use when traveling or irregularly. However, if you wear a one-day lens for more than one day, you should not wear it for a few days because of side effects.
2) Two-Week Soft Lens: A lens used for two weeks in the morning, removed in the evening, stored in a cleaning and preservative solution.
3) 1-month soft lens: This lens is used for one month after being put in the morning and removed in the evening.
4) Soft lens for three months: This lens is used for three months after being put in the morning and removed in the evening.
5) Color lens: A lens that changes the color of the iris area of the eye. It can be contacted with both disposable lenses and continuous wear lenses, and there are one-tone lenses, two-tone lenses, and three-tone lenses depending on the color.
6) Iris Lens: This lens is used to cover the iris deformed due to surgery, inflammation, or whiteness due to turbidity. It is called an iris lens because it is shaped like an iris.
7) Astigmatism correcting lens: Astigmatism correction of astigmatism correcting lens is worn with a daily wear lens.
8) Silicone Hydrogel Lens: Compared to the existing soft lens made of hydrogel, the addition of silicon significantly improves the oxygen permeability, thereby solving the low oxygen permeability problem of the existing soft lens.
Early models had a disadvantage of poor fit, but recently, models that solve many of these problems have been introduced. Depending on the model, the license period is different, but the advantage is that one to four weeks of continuous wear is possible.
3. Features of Soft Lens
The advantage of soft lenses is that the eye easily adapts and the initial fit is good. Disposable for one-time use is convenient. It is good for people who enjoy sports due to less detachment of the lens, and less corneal deformation than RGP lens. There is very little spectacle blur, which is difficult to see if you remove the contact lens and immediately wear the glasses. Due to the large diameter of the optics, there is less glare than RGP.
The disadvantage of soft lenses is that they are soft and easy to tear (especially disposables). Low oxygen permeability can cause congestion and corneal edema with prolonged wear. Severe astigmatism is difficult to correct, and there is a risk of bacterial infection due to poor circulation of the tear when wearing the lens. Since the lens itself is a material that absorbs water, there is a high possibility of causing dry eye. When the tear layer is unstable, the lens changes shape, making it difficult to mount correctly.
Prolonged wear can cause allergic conjunctivitis, such as giant papillary conjunctivitis (GPC). General eye drops are deposited on the lens when worn, so eye drops other than wetting agents (or artificial tears) cannot be used. Water sports, such as swimming increase the risk of bacterial infections from contaminated water.
1. What is an RGP lens?
Hard lenses are made of more stable and rigid materials than soft lenses. In the past, it was called a hard lens because it was made of PMMA lens that does not supply oxygen because it was made of hard acrylic material, but now it is an RGP lens made of a material that is strong and provides oxygen supply easily by combining silicon and fluorine compound. All are called RGP lenses. Due to its material properties, it is suitable for visual acuity correction is severe or irregular corneal patients, and it is less dry.
2. Types of RGP Lens
a) Aspherical lens: Aspheric surface means not spherical surface. It is a curved surface that is generally flattened from the center to the periphery. It is similar to the surface of the rugby ball. The cornea of our eyes is also in this aspheric shape so that the aspherical lens fits in line with the curvature of the cornea. Compared with the spherical lens, wearability is good, tear circulation is good, there are few side effects such as lens stiffness and hyperemia, and it is good for astigmatism correction. Prescriptions are more complicated than spherical lenses, and poor vision can cause poor vision.
b) Spherical lens: A spherical surface is a curved surface with the same curvature at the center and periphery. In general, a spherical surface is a surface of a public ball such as a baseball or soccer ball. The spherical lens is shaped like a circle. Since vision is less affected by centering than the aspheric lens, general vision correction is good. However, in the eyes with severe astigmatism, lens deviation can occur, and prescription can be difficult. Compared to the aspherical lens, foreign body and fit may be inferior and corneal deformation is easy.
3. How to wear RGP lens
Unlike soft contact lenses, the lens is not attached to the cornea but remains on the tear layer of the cornea. This principle is beneficial to the health of the eyes (especially the cornea) due to the good circulation of tears and oxygen supply through the tears. There is a movement due to the structure floating on the cornea, which makes it feel the paint at the time of initial wearing, but as time passes, the foreign body decreases and becomes more comfortable as the tear layer stabilizes and adapts to movement.
4. Features of RGP Lens
The advantage of the RGP lens is that it is less likely to deposit on the lens surface compared to the general soft lens, and is easily cleaned. Once adopted, it feels comfortable even in prolonged wearing. It is more economical in the long run than soft lenses. Long life of the lens, good circulation of tears and oxygen supply, fewer complications of the cornea and conjunctiva, conducive to eye health. Correction (especially aspherical lens) in the presence of corneal surface curvature or corneal astigmatism occurs less frequently than soft lenses. Allergic reactions occur minimally.
Disadvantages of RGP lenses are their initial discomfort, and some patients may not be able to adapt. Initial adaptation period (1-2 weeks) is required. Dust or other foreign matter can get into your eyes and cause temporary pain. There is a risk of lens detachment or loss during exercise. Prescribing a lens requires more careful skill and time. If you make a mistake, you may have increased redness or dryness. Due to the small diameter of the optics, peripheral flares may occur at night or in dark places.