Contact lenses - what's the difference?

Nowadays the choice of contact lenses can be quite bewildering. There are many manufacturers, types, products and replacement intervals.  So what's the difference?


Hard or Rigid Gas Permeable

The very first contact lenses were hard lenses. Primitive versions date back to the late 19th century, but hard lenses as we know them today first gained mass appeal in the 1960's.

Despite requiring some initial adaptation, they actually provided superb vision. However because they were made of PMMA, they did not allow any oxygen to reach the eye. For optimum eye health, a good supply of oxygen to the cornea is essential.

Accordingly, research and development in the 1970's led to the introduction of Rigid Gas Permeable (RGP) lenses which solved this problem. RGP lenses offer excellent quality of vision and, unlike soft lenses, won't tear so they're exceptionally durable. They're particularly good for people with complex prescriptions (such as high amounts of astigmastism) or pathology such as keratoconus.

Our speciality is a modern variant known as Wave. Using corneal shape data from a device known as a topographer, we can individually design a custom RGP contact lens that accurately mirrors the cornea for the most precise and comfortable fit available. In most cases, vision quality will be even better than with a standard RGP or soft lens.

We also fit Orthokeratology (or Ortho-K) lenses. Here a rigid gas permeable lens is worn overnight to temporarily reshape the cornea. When removed in the morning, this provides corrected vision during waking hours. Research has also suggested that, in young people, this might halt the progression of short sightedness. You can read more about orthokeratology here

 

Soft Lenses

Traditional soft contact lenses first became widely available in the early 1970's. Their main attraction was superb comfort almost immediately after insertion. However, the oxygen transmission of the lens materials was initially fairly limited. In addition, lenses that were worn for more than a few months tended to attract stubborn deposits which reduced the overall comfort and visual performance. Manufacturing techniques also dictated that the lenses were thicker than they otherwise needed to be, and were only available in a certain range of powers.

By the early 1990's, improvements in manufacturing methods helped solve some of these problems. Lenses could not only be made thinner and more comfortable, but in a wider range of powers and at a reduced cost which would allow regular replacements (thereby reducing the problem of deposits). Monthly and fortnightly replacement lenses therefore became the norm. Later, daily disposables were also introduced.

Toric lenses became more widely available (and affordable) to correct astigmatism, as did multifocals for presbyopia or near vision deficiencies.


A further breakthrough came in 1998 with the availability of silicone hydrogel lenses. These combined the extremely high oxygen permeability of silicone with the comfort and clinical performance of conventional hydrogels, offering outstanding comfort and eye health.



The arrival of silicon hydrogels also allowed the introduction of specific lenses approved for overnight or extended wear. Previously overnight wear was not possible without the risk of causing damage to your eyes.  They also allowed the development of better coloured lenses (to change or enhance the colour of your eye). Previously, coloured lenses often caused problems because they severely restricted the oxygen transmission to the eye.


Ultimately the most suitable lens for you will depend on a number of factors, such as your prescription, lifestyle, tear supply and geometry of your cornea. During your contact lens consultation, we will discuss this with you and give our honest recommendations. Meanwhile, if you require any further information or advice, please don't hesitate to ask.