GENERAL FACTS ABOUT CONTACT LENSES
A contact lens is a lens that is placed on the cornea for corrective, cosmetic or therapeutic purposes. Leonardo da Vinci is credited with introducing the first idea for contact lenses in 1508. More than 300 years later the first lenses were produced. It was not before the second half of the 20th century that mass usage of contact lenses started. Today, more than 150 million people are estimated to be contact lens users, and they opt to wear contact lenses because of their personal appearance and practicality. Certain conditions, such as keratoconus or aniseikonia cannot be corrected by eyeglasses so that contact lens is the only choice. Contact lenses and contact lens care solutions are medical products so that their market is regulated by law. They are one of the safest medical products ever produced, but still complications may arise. About 6% of all contact lens users have experienced some kind of these problems related to contact lens usage every year. The majority of problems are insignificant and have no consequences for the user. However, there may be also serious and vision-dangerous complications if the user fails to follow the wear and care instructions. Also, purchase of medical products from unauthorized suppliers without regular eye control by professional persons, and failure to follow the rules about safe usage and handling of contact lenses lead to high risk of medical complications related to wearing contact lenses.
BASIC TYPES OF CONTACT LENSES
CONTACT LENSES CAN BE CLASSIFIED ACCORDING TO SEVERAL CATEGORIES:
ACCORDING TO TYPE OF MATERIAL
- rigid (made of obsolete PMMA material that has good optical and mechanical properties but lacks oxygen transmissibility which is necessary for normal eye metabolism)
- rigid gas permeable lenses are produced from advanced polymers that have excellent optical and mechanical properties, and high oxygen transmissibility, so that they are, therefore, the healthiest for the eye and provide best possible vision to the user;
- soft contact lenses (made of soft polymers). The most advanced soft material today is silicon hydrogel.
ACCORDING TO PURPOSE
- corrective (to correct visual acuity)
- cosmetic (to change the appearance of the eye)
- therapeutic (to protect eyes due to certain medical conditions, after injuries or surgery, and as medicine carriers slowly delivering the medicine into the eye from the contact lenses).
ACCORIDNG TO METHOD OF CORRECTION
- monofocal (for the correction of distance vision)
- multifocal / bifocal and progressive (for the correction of distance and near vision)