Contact lenses come in various types according to different factors
. When it comes to lens materials, contact lenses can be classified into soft lenses and rigid gas permeable lenses. According to lens color, there are colored contact lenses and transparent contacts. Another aspect that can be used to categorize contact lenses in various brands is wearing or removal schedule. Depending on this factor, contact lenses are grouped into daily wear contacts and extended wear contacts.
In fact, the majority of contact lenses sold on the market are daily wear ones which only last one day and should be removed at night and properly stored in a lens case. This is the commonest type of contact lenses. And the criticism towards contact lenses such as inconvenience and excessive daily care mainly comes from daily wear contact lenses. This kind of criticism is quite understandable because daily wear contact lenses do require much daily care and maintenance such as cleaning and disinfecting.
In order to offset some of the shortcomings of daily wear contact lenses, extended wear contact lenses come into being. Another more vivid name of this type is day and night soft contact lenses. It means that this form of contact lenses can last in the day and the night without removal. This feature or advantage eliminates much of the lens care caused by daily lenses. According to different replacement schedules, extended wear contact lenses that have been worn for continuously several days can be simply discarded or removed and reused later.
One of key requirements of extended wear contact lenses is that they must be made of special materials that allow more oxygen to pass through and reach the eyes. The eyes need sufficient amounts of oxygen to produce adequate water, which is essential to moisturize the eyes. This is a critical ability for the eyes to realize self-protection by washing away debris and dirt that often accumulate on the eye surface.