Brief introduction to hard contact lenses development
Friday, February 13th, 2009 Subscribe To Our Feed
Originally, when the hard (pmma) contact lens was developed, the correction of astigmatism was not much of an issue due to the fact that this lens material was rigid and therefore did not follow the contour of the irregularities of the cornea and so the tear film between the lens and the cornea of the eye would function as an extra lens which would compensate the irregularities and also most of the astigmatism caused by the cornea.
With the onset of soft contact lenses, the problem of correcting astigmatism suddenly re-emerged because this type of lens material (as the name already suggests) does follow the contour of the cornea and therefore does not compensate for astigmatism. The result was that the popularity of soft contact lenses was somehow slowed down because most hard contact lens wearers who wear refitted with soft contact lenses suddenly noticed that their vision was not quite as sharp with the newly fitted soft lenses. So the main reason for the refit from hard to soft lenses was the advantage of comfort or the fact that the soft lens did not spontaneous fell out during contact sports. Other reason for contact lenses users to stay with the rigid hard lenses was the cheap price. The pmma lens was made out of Perspex and therefore needed very little care. Most wearers would just store the lens dry during the night and use a few drops of saline to help to insert the lens in the morning. Some wearers even used saliva to clean or wet the lenses before inserting it in their eyes.
The next development was the gas permeable (hard) rigid lens which was to replace the pmma hard lens. This lens was as uncomfortable as the pmma lens and also needed a long adaptation period for the wearer to get used to. The advantage of this type of lens was that the oxygen transmission to the cornea improved and therefore could be worn for longer periods without complications such as oxygen deprivation which could lead to cornea oedema and other symptoms. The correction of astigmatism was again not much of an issue.
The main drawback of this type of lens was the depositing of protein molecules on the lens surface especially when the lens wearer did not adhere to a strict cleaning regime. The lenses users had to spend additional money for the lenses maintenance and the average lenses replacement time went down from ten plus years for the pmma lens to four years for the gas permeable lens. Most optometrists were able to convince their patients of the benefits of this new development although a considerable number of successful pmma lens wearers were not very happy with the increased spending and protein depositing of these new lenses.
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