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Many people with Keratoconus require contact lenses to achieve sufficient visual acuity. Fitting a Keratoconic cornea with any lens can be more difficult and challenging than fitting a healthy eye. It is important to find an experienced and understanding contact lens fitter. It can take many fitting sessions and up to two or three sets of lenses before the right lenses are found.
If KC progresses the shape of the cornea will change and at this stage a new contact lenses fitting may be required. Therefore a person with Keratoconus may require many lens fittings during their lifetime.

Below you will find the most common types of contact lenses used for Keratoconus.

RGP lenses = Rigid Gas Permeable lenses

RGP lenses or Rigid Glass Permiable lenses are one of the most common type of lenses to be used in the treatment of Keratoconus. It is important to know that RGP stands for the material of the lens not the actual lens itself. Although the two names are often interchanged there are infact numerous RGP lenses on the market with different designs and attributes. RGP lenses are sometimes called hard lenses or rigid lenses. they work by creating a smooth surface on the cornea. When fitted on the eye they create along with the tears a smooth optical surface for light to enter the eye. One of the myths of rigid contact lenses are they push and squash the cornea into shape. This is not true the front of the lenses provide the spherical shape, the back of the lenses is then filled with tears canceling out the irregularities of the cone.

Soft lenses are made from gel like plastic containing mostly water . They are normally used for the early stages of Keratoconus.

Soft Toric lenses are made from the same material as soft lenses and have many similar attributes. Soft Toric lenses correct the astigmatism of Keratoconic eye much better than a regular soft lens. The main difference is that soft toric lens has two powers (one for astigmatism and the other for myopia or hyperopia) while regular (spherical) soft lens has the same power all around the lens. For soft toric lens to achieve good visual acuity it is vital that it remains in the position unlike regular soft lens, which can move freely around the eye. Due to this attribute it can take more time to get perfect fit with soft toric lens than with standard soft lens.

These lenses have a rigid center but a soft outer skirt, improving comfort level. These lenses are normally used if comfort and vision cannot be achieved with RGP lenses. There are some draw backs, they have less oxygen permeability which can create problems, also the skirt can sometimes be too tight. Not everyone is able to wear softperms despite their comfort level, due it's associated problems. A new hybrid lenses is in development, which will have increased permeability. They are also generally more expensive than RGPs and the connection between the soft skirt and hard center is often vulnerable to tearing meaning they are replaced more often.

These lenses cover the whole of the idea and have many advantages over RGP and softperm lenses. Since they rest of the white part of the eye they are much bigger than RGP or soft lenses and are reported to be more comfortable and also do not slip off the cornea due to their size.

Piggyback technique is based on wearing a RGP lens over standard soft lens.

Useful links :

ROSE K Lens official site

Excellent information about various types of lenses and care of them

Management of Keratoconus with contact lenses