• The contact lenses are normally used to accurate visualization, even though some public wear colored contact lens to improve or alter their eye color.
• The contact lenses can be classified based on type of material, replacement cycle, wear schedule and special applications:-
  1. Material types (soft, hard and gas-permeable),
  2. Replacement schedule (one year, daily, fortnightly, monthly and quarterly),
  3. Wear schedule (Daily wear and extended wear),
  4. Special types (torics for astigmatism, UV-blocking contacts, bifocals etc).

• In the starting PMMA, the material of the hard corneal contact lens which came out in 1957. The material did not convey oxygen and was actually tough to fit. Until the early 70's, PMMA was the only contact lens material.
• At that time the variety of "soft" or "hydrogel" resources started coming out. By 1980 these latter materials conquered the market--to the extent that some young doctors forgot how to fit hard lenses. The newer materials "breathed", were much more relaxed, and were much easier to fit but they wear out, got coated, were indicted in a number of long term corneal troubles, and the optics was not as superior as stiff lenses.
• In the late 70's a variety of RGP materials came out. These materials are rigid, but not quite as rigid as PMMA. They convey oxygen and have superior optics than hydrogel materials. They are much easier to fit than PMMA lenses but share many of the advantages and fitting characterizes. The ease of RGP lenses with modern designs is greater than PMMA but much inferior than hydrogel.

• Soft Contact Lenses are prepared from a water absorbing material called HEMA (Hydroxy Ethyl Metha  Acrylate) & are very flexible to handle and comfy on the eyes.
• Inside the sphere-shaped category are the conventional and disposable soft lenses. The first comprises a single pair that can be worn for a period of one year on a daily basis during waking hours.
• Disposables are the most hygienic option as they are replaced after a particular period —daily, fortnightly, monthly or quarterly.
• Hard contact lenses are made of some variant of polymethyl methacrylate (PMMA) and are obsolete.
• RGP lenses are semi-rigid lenses prepared generally from silicones which permit oxygen through to the eye.
• Toric soft lenses are used in cases of high cylindrical power or astigmatism.
• An easy choice over semi-soft lenses, it is offered as both conventional and disposable.
• Bifocal contact lenses are recommend for those who favor contact lens improvement for Presbyopia or difficulty in near vision. These are presently obtainable only in disposable choice.
• Cosmetic contact lenses are obtainable in a variety of colors and shade, in both power and Plano, with usual and disposable choice. These are mainly worn to improve looks.
• Contact lens market in India is dominated by soft contact lenses. The market for disposable lenses is growing at a higher rate as they are more hygienic and require lesser maintenance.

The Optics of Rigid Contact Lenses:

General Considerations:

1. Rigid lenses are comparatively tiny, usually about 9.0mm diameter.
2. RGP lenses should move a bit to convey O2 through tears to the cornea. Movement or "lag" generally is approximately 2-3mm.
3. The uneasiness of the lenses is mainly due to lid sense, particularly the upper lid going over the lens.
4. As a result, patients often stop blinking generally, and 3-9 staining, results from drying of the parallel cornea.
5. These days, lenses are often fit so they tuck under and move with the upper lid, thus reduce lid feel.
6. The lenses are paper slim, <0.1mm, and fairly breakable and stretchable.

• Soft Contact Lenses are made from a water absorbing polymer called HEMA (Hydroxy Ethyl Metha Acrylate). It has hydrophilic qualities, i.e., it can soak up water and still retain its shape and optic functions.
• Contact lenses may be formed by cutting a blank on a lathe or by molding process.

1. Recommend displacement- generally 1 day,1-2 week, 1 year
2. Wearing Indication
3. Lens Material (edge corrected)
4. Lens Material  (non-edge corrected)
5. Water Content-generally 38%,47%,58% etc
6. Visibility Tint- should be yes.
7. UV Blocking-should be yes
8. Inside-Out Mark
9. Center Thickness
10. Parameters (Power Range)