Hard contact lens use

 
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Types of contact lens
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Hard Contact Lenses

What are hard contact lenses?

Hard contact lenses are made from rigid materials like glass and plastics. The earlier types are rarely prescribed now, though they had several advantages. They were easy to wear and remove and easy to maintain. They were durable and cheap. Today the lenses made from rigid gas permeable materials are practically the only hard lenses available.

When are hard contact lenses used?

Like all contact lenses they are used for correcting vision in near sightedness, far sightedness and in some astigmatism cases. Hard contact lenses, by and large, provide good vision correction.

What are the types of hard contact lenses?

Glass contacts, PMMA contacts and RGP contacts are the three main types. The first two are almost obsolete. Presently RGP contacts are practically the only hard contacts still used.

Glass contact lenses: The first contact lenses, made from glass, caused a lot of irritation and could be worn for only limited periods. These were soon discarded.

Polymethyl methacrylate or PMMA lenses: Glass lenses were replaced by lenses made from a mixture of plastic and glass called polymethyl methacrylate or PMMA and commonly known as plexiglass. These were the first contact lenses with mass appeal. They were lighter and more convenient. But they came with their own side effects.

PMMA lenses did not allow oxygen to enter the cornea, thus increasing the risk of corneal and other infections. This lack of oxygen permeability in PMMA lenses was a serious disadvantage. Also PMMA lenses were quite uncomfortable for the first few weeks of wear. Despite these disadvantages, PMMA lenses are still occasionally worn but have become largely obsolete. They are cheaper than the latest contact lenses.

Rigid gas permeable or RGP lenses: These are the modern version of the hard lenses. Today when people talk about hard contact lenses they mean RGP lenses. After the 70s, superior plastic materials, which had higher oxygen permeability and were also rigid, were developed. Lenses made from such materials are called Rigid Gas Permeable or RGP lenses to distinguish them from soft contact lenses that are also oxygen permeable.

What are the benefits of RGP lenses

  • Rigid gas permeable lenses are less flexible than the soft lenses, since they are made from a mixture of semi-rigid materials. This means they retain their shape even when you blink. They provide better vision than what you would get with soft contacts.
  • They are very durable and provide excellent vision clarity and can serve you for up to a year.
  • Since they are longer lasting, RGP lenses can be cheaper than soft lenses in the long term.
  • They can be worn occasionally or regularly but need to be cleaned, disinfected and stored properly.

What are the unique benefits of RGP lenses?

RGP lenses offer a number of unique benefits, they are:

  • These lenses can replace the natural shape of the cornea with a new refracting surface. This allows RGP lenses to provide good level of vision in people who have astigmatism or distorted corneal shapes as in keratoconus. Conventional glass spectacles and soft contacts cannot correct such visual impairments.
  • People who are very fussy about their clarity of vision prefer RGP lenses.
  • According to many people, the best bifocals are made from RGP material. It is of special benefit to people with presbyopia since RGP lenses come in several bifocal and multifocal designs.
  • For children, RGP lenses can slow down the progression of near sightedness.
  • RGPs are used for orthokeratology where specially designed lenses are worn during sleep to correct the corneal shape and improve the vision.

What are the disadvantages of RGP lenses?

  • These lenses can take longer than soft lenses to get used to.
  • Unlike soft contacts, you will have to wear RGP, if not daily, at least very regularly to get maximum comfort. Soft contacts worn after a week don’t need time to adjust. But RGP lenses worn after a similar period will certainly need some time to feel comfortable.
  • Some people experience what is called ‘spectacle blur’, a blurring of vision when the lenses are removed that persists even after wearing glasses. Though a temporary phenomena, it makes RGP a full time wear causing inconvenience for some people.
  • RGP lenses need greater care and more rubbing during cleaning.

Conclusion

RGP lenses, although needing more time to adjust, are as good as soft contacts. Some vision problems can be corrected by only RGP lenses. But they require greater care than soft contacts.