Imagined by Leonardo da Vinci in the sixteenth century, contact lenses will only be produced three centuries later. At the end of the 19th century, German, Swiss and French doctors and opticians developed glass contact lenses, based on an idea of the British astronomer Herschel, namely to use a mold of the patient’s eye …
These first coarse heavy glass contact lenses covered the entire eye and did not let oxygen pass, making them very uncomfortable.
In the 1930s and 1940s, American opticians introduced hard plastic materials into contact lenses for the first time, the central part of which remained in glass. The first fully plastic lenses appeared in the 1950s. But it was only in the early 1970s that the diameter and thickness of contact lenses reached current standards. But despite these 40 years of evolution, they remain uncomfortable for most users due to their rigidity. A disability that will quickly disappear due to the arrival in the market in 1971, revolutionary lenses signed Bausch & Lomb. These soft lenses are flexible and absorb water. Thinner and more comfortable than the previous ones, these new lenses offer a real alternative to wearing glasses for all people suffering from ametropia. Today, soft lenses account for almost 90% of sales of contact lenses.
Hard or Soft lenses?
This choice depends on your visual defect, your correction, your lifestyle, your tastes and finally your ability to secrete tears … The most modern, known as RPG (Rigid Gas Permeable), particularly satisfy carriers susceptible to ocular dryness, due to their high oxygen permeability, however, the difference in oxygen permeability Between hard and soft lenses tends to disappear due to the arrival on the market of soft silicone hydrogel lenses, a material which allows up to 7 times more oxygen to pass than the usual flexible lenses and which allows them to be kept during One month, 24 hours a day without danger of infection or risk of damaging the eyes.
Hard or soft, it is your ophthalmologist who will determine the lens that suits you best.
Why is oxygen permeability important?
In order to provide perfect transparency, the cornea is the only non-vascularized tissue. In fact, she “breathes” only through the oxygen of the air and tears. For a better comfort and a lower risk of infections, it is therefore imperative that the lenses, rigid or flexible, guarantee a maximum oxygenation of the cornea.
Between soft and hard
– Soft lenses have a predetermined life span, which can vary from one day to two years. Conversely, hard lenses do not have a predetermined lifetime. It is their state that determines whether the time has come to change them or not.
– Soft lenses are almost always immediately comfortable, whereas it takes a time to adapt to rigid lenses which can range from a few days to a month. However, this time lapse, rigid lenses are as comfortable to wear as soft ones.
– Conventional soft lenses contain between 40 and 80% of water which makes them permeable to oxygen, soft and comfortable. However, this forces them to be immersed in a liquid as soon as they are deposited in order to prevent them from dehydrating. Silicone hydrogel lenses, because of their lower water content (26%) suffer less from this disadvantage.
– Most rigid lenses are more expensive than soft lenses, but their frequency of replacement is less regular.
– Rigid lenses perfectly correct corneal astigmatism, whether minimal or important and give the eye a sharp image.
– Because they allow a very good visual quality, rigid lenses are widely used in children. They allow them to acquire optimal visual maturity.
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