The material of the contact lens, such as hydrogel, is soft and pliable. Patients find these lenses significantly more comfortable. The oxygen permeability of the material depends on its water content, which may range from 36 % to 85 %. The higher the water content, the better the oxygen permeability. However, it is typically lower than that of rigid lenses. The material is more permeable to foreign substances, which can accumulate in it. At 12.5-16 mm, flexible lenses are larger in diameter than rigid lenses. Flexible lenses are often supported by the limbus. The lens is often displaced only a few tenths of a millimeter when the patient blinks. This greatly reduces the circulation of tear film under the lenses. This limits the maximum daily period that patients are able to wear them and requires that they be removed at night to allow regeneration of the cornea. Deviation from this principle is only possible in exceptional cases under the strict supervision of a physician.
As the lenses are almost completely in contact with the surface of the cornea, corneal astigmatism cannot be corrected with spherical soft lenses. This requires toric soft lenses.
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