Silicone hydrogel lenses

Silicone hydrogel lenses are the latest generation of lenses which are soft, allow a greater amount of oxygen to reach the eye and, can be worn for up to 30 days continuously.

These lenses first appeared at the end of the 1990’sdue to the inclusion of silicone as one of the materials. This has the advantage of a high level of oxygen permeability which means more oxygen is transmitted to your eyes.

This oxygen transmission is vital for eye health, particular the cornea which needs oxygen to enable you to see the world around you. A lack of oxygen causes the cornea to become less translucent, distort and less effective at detecting pain and other similar problems. Scarring develops on the cornea which affects the eyesight.

A sign of a lack of oxygen to the eye is eyestrain and swelling. This is a problem for contact lens wearers which mean choosing a lens which allows a greater proportion of oxygen to pass through the cornea.

Silicone hydrogel lenses are ideal for this purpose.

Advantages of silicone hydrogel lenses

The main advantage is this ability to allow an optimum amount of oxygen to pass through the cornea. This is an exciting development when compared to other types of lenses and means improved comfort and longevity of this type of lens.

Silicone hydrogel lenses are able to transmit five times more oxygen to the cornea as compared to other lenses.

(Source: www.allaboutvision.com)

Plus they are less water based than other types of lenses which reduces the risk of dehydration. The issue of dehydration has been noticed by people who find that their lenses have dried out by the end of the day. This can mean dry, tired and sore eyes.

Basically, the greater the amount of water a contact lens has the greater the risk of dehydration. This is a problem with traditional hydrogel lenses but less so with the newer silicone hydrogel lens.

Improved oxygen permeability

How does the silicone hydrogel lens compare to the hydrogel lens in terms of oxygen transference?

Many of the soft contact lenses are produced from substances known as ‘hydrogel polymers’ (types of plastic) which are also water bearing. The actual lens is not capable of transmitting oxygen to the eye but the water bearing properties are. So this water based plastic allows oxygen to pass through the lens and into the eye.

But there is a catch with this. There is a finite limit to the amount of oxygen that can be transmitted by water and the higher the amount of water the greater the chance of dehydration especially after a long period of wear.

Conversely, the silicone hydrogel lens is oxygen permeable which means that it can enable oxygen to reach the eye. This is done via a combination of both the water and oxygen content of the lens.

Enable continuous wear

As a result of this improved oxygen transference to the eye; the 30 day continuous lens has become available for general wear. This type of lens can be worn in the day and during the night for a period of up to 30 days.

But concerns were raised about the 30 day lens due to a risk of eye infections such as keratitis. Some people experienced eye problems such as this from wearing their contact lenses overnight which led to the development of lenses such as the silicone hydrogel variety.

Silicone hydrogel lenses are the most commonly worn soft lens in the UK. This includes daily disposable, daily wear and even continuous wear lenses. But discuss these options first with your optician particularly in regard to the 30 day continuous wear lenses.

These lenses were designed for continuous wear which includes night time wear although there are arguments for and against this. There is a small risk of conditions such as keratitis although this tends to apply to the standard hydrogel lenses and not the silicone hydrogel variety.

Not suitable for everyone

But it is important that you talk to your optician before wearing continuous wear lenses. Not everyone is suited to this type of lens which may mean an alternative. Most silicone hydrogel lenses are designed to be worn on a daily or two weekly basis so consider these options carefully when deciding whether or not to wear this lens.

Oxygen performance is one factor but there are other factors to take into account.

Your optician will be able to recommend a suitable type of contact lens dependant upon your particular needs and preferences.