Role of Contact Lenses in Myopia

The use of contact lenses and the rapid advances in the technology of their manufacture during the last decade has undoubtedly contributed to treatment of myopic. The wearing of contact lens corrects myopia just as spectacles’ glass.

It goes a step further in providing natural visual field and, above all, stops the myopia from increasing at an alarming rate. The last factor is singularly the most favorable point in contact lenses.

It is easy to understand that the placement of the lens on the surface of the cornea brings a film of tears between the lens and the cornea. This film of tear fluid, which has the same refractive index as the cornea, neutralizes any irregularity in the curvature of the cornea. The contact lens of a myopic has a minus number power ground into it from the spectacle power prescription given by the eye specialist. However, in practice, high-powered myopic with high astigmatism benefit additionally by the contact lenses.

There are two types of basic contact lenses-hard and soft contact lenses.

Hard Contact Lenses

A hard lens is made of highly inert and refined plastic material which rests on the cornea. It has no water and oxygen content and the nutrition to the cornea is supplied by the tear film and atmospheric air in and around the lens. These lenses cannot be worn for long stretches and certainly not during sleep. They rest lightly on the cornea due to surface tension. They move with lid movements. A clear area must be there between the cornea and the surrounding white sclera for free tear flow. There is a tendency for them to slip off if not properly fitted. This is perhaps their disadvantage. They correct even high astigmatism and are economical in cost. The hard contact lenses now do not find favors with eye specialists. They have been replaced by semi soft, comfortable and gas permeable lenses.

Soft and Semi-soft Contact Lenses

The soft lenses have a high water and oxygen content. They are very light, thin and collapsible, like a section of a balloon. They rest more comfortably and tightly on the cornea and the surrounding sclera and can be worn for a greater length of time. They do-not slip off or move with the lids. Their high water and oxygen content is a great advantage. They have a tendency to wear off if not carefully handled. They are delicate and require expert handling and sterilizations. Also they are more expensive. The semi-soft (gas permeable) contact lens have now replaced· the hard lenses for wearing in astigmatism. They are comfortable and have a long life.