It is a very thin plastic lens which is placed on the in front black round part of the eyeball known as cornea. It contact over the eye directly. Basically, contact lens uses medically for visual defect correction, it is generally colour less, but it has very lightly tinge by which we can easily identify or can handle it nicely. Sometimes we can use it cosmetically or therapeutically also.
2 types of Contact lens are – Hard lens and Soft lens.
- Hard lens is made of Polymethyl methacrylate (PMMA). There is another type of hard lens which is called Rigid gas permeable (RGP)lens and it is a refined form of hard lens made by silicon acrylate a polymer of PMMA.
- Soft lens is made by Hydroxy-ethyl-methacrylate (HEMA). This is also the part of PMMA. Now silicon hydrogel material is also very acceptable because its ability to oxygen permeability.
Parts of Contact lens—
- DIAMETER of the contact lens is written by millimetres which is generally 2 to 3 millimetres larger than normal cornea in case of soft lens and in case of hard or RGP lens it is 1to 2 mm less than cornea.
- Curves of lens – It is a base curve or posterior central curvature on the back surface of the lens which is ready to fit on corneal front surface.
- Edges of lens is very finely designed to give a comfort to use lens for eyelids and corneo-scleral junction.
- Power of lens which is measured by Dioptres. Mainly the central anterior curve of lens or the optical zone of lens.
- Thickness of lens is very compatible to eye and depend on the posterior vertex power of lens.
- Tint is the colour of lens. Most of the time it is bluish or for coloured lens is colourful.