The History of contact lenses
The first contact lens – made of glass – was developed by Adolf Fick in 1887 to correct irregular astigmatism. These early lenses were uncomfortable and were not worn for long. Until the development of keratometers (instruments to measure the curvature of the cornea – the translucent front surface of the eye) an individual contact lens was made by taking an impression of the eye and fashioning a lens on a mould. The modern contact lens, developed by Kevin Tuohy in 1948 is made of plastic, and rests on a cushion of tears.
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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.
The Fitting Procedure
An initial inquiry by a potential contact lens wearer will be answered with a careful 'history and symptoms' to establish the best type of contact lens for the particular person in question. This decision will be based on the requirements of the patient – likely duration of contact lens wear and the types of activity the patient will be engaged in whilst wearing the lenses.
Most patients will be offered a 'trial' with either RGP or soft contact lenses. This consists of an appointment during which contact lenses are inserted and the patient can then wear the lenses for a short period to establish levels of tolerance.
The tolerance to any particular type of lens, together with information gleaned at the history taking will help to establish what type of lens will best suit a particular patient.
Bifocal & Varifocal Contact Lenses
It is now possible to supply several types of bifocal and Varifocal contact lens, in both soft and RGP designs. These are obviously new developments, but already at Gamble & Creswell, we have quite a few patients wearing these types of lenses with great success.
Whilst they will not suit everyone they can replace a pair of reading over spectacles – the usual means of correcting near vision for a patient (usually over 45) who requires different optical corrections for both distance and near.
Other 'presbyopes' manage well with 'monovision' where one eye is corrected for distance and the other for near. The image in the fellow eye being 'suppressed' when not required.
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