Soft Contact Lenses

Were introduced in the 1970’s and are made from water absorbing plastic gel. These are very comfortable to wear, but because they absorb whatever fluids they are in contact with, in sponge like manner, problems with maintenance of sterility make them the lenses most likely to result in re-current eye infection.

Eye infections resulting from contact lens wear, and especially non-compliance with contact lens care regimes can be of a trivial, merely annoying nature, or potentially sight threatening diseases such as ‘pseudemonous’ infiltration.

The hygiene problems associated with soft contact lenses wear have resulted in the more recent development of regular and frequent replacement lenses. These include: -

Monthly disposables – Usually a patient collects six months supply of contact lenses (6 left & 6 right) and the necessary care solutions. The contact lenses are worn on a daily basis, and on removal are cleaned thoroughly according to the instructions of the care regime recommended. Once a month the pair of lenses are discarded and replaced.

Daily disposables – Arguably the safest form of soft contact lenses correction. Single use lenses – worn for one day only, and therefore require no cleaning. There is no cleaning procedure for the patient not to comply with (!) and as each lens is used once only, the risk of infection is considerably reduced.

Extended wear (soft) contact lenses – Big advances in material technology has allowed the introduction of certain types of lens, which are capable of being worn for up to a month at a time. The potential for infection is obviously increased and such lenses require careful monitoring and special aftercare procedures.

Hard Contact Lenses/ RGP

During the second world war, it had been noted that pilots who had suffered eye injuries from shards of Perspex from the canopies of their aircraft, had a distinct lack of inflammatory reaction to the embedded fragments of plastic. These could stay in the eyes’ tissues as an inert substance and it was reasoned that clinical quality perspex (PMMA) would make a good basis for a material from which to fashion a contact lens.

These PMMA ‘contact lenses’ fitting within the limits of the cornea and covering the pupil area have largely been replaced by RGP (rigid gas-permeable) contact lenses. These look similar to hard contact lenses but are made from a range of oxygen permeable polymers. This has resulted in greater cornea health and longer wearing times. It could be argued that RGP lenses represent the healthiest option for the cornea, and their ability to correct astigmatism makes this type of lens a very popular option today.