Table 1.

Different contact lenses: cons and pros.^58,59

Lens type	Advantages		Disadvantages
Soft	- Suitable for astigmatism in the early stages of mild keratoconus	- Stability - Tolerance and comfort - Adequate optics	- Fitting is not always possible - May poorly hide uneven corneal topography
RGP	- Correction of irregular astigmatism by tear film - High visual acuity		- Tear film bubbles impair vision - Unstable and off-center fit if not large enough - Low tolerance and comfort
Hybrid	- Stability - Comfort and tolerance - Correction of irregular astigmatism	- Exchange of tears without obstruction - Good optical performance - High visual acuity	- More difficult to apply, fit and remove - More frequent replacement - Higher costs - Longer time to settle
Scleral	- No contacting the cone of the eye - Therapeutic benefit for dry eyes by trapping tears behind the lens - Concealing very extensive regions of corneal irregularity - Larger diameter - Greater tear capacity	- More movement - Increased decentration - Smaller diameter - Simple to use - Some don’t require fluid for insertion, resulting in fewer bubbles - More space for support in the bearing zone	- Wrong diameters have distinct advantages - Vertical movement is uncomfortable - Four to five times as expensive as soft contact lenses - Corneal edema - Neovascularization - Corneal abrasion and mechanical irritation - Midday fogging and protein deposits - Giant papillary conjunctivitis
Piggyback	- Improve mechanical tolerance and centration - Comfort and tolerance - Better correction - A highly permeable oxygen structure - Fewer changes in the number of corneal endothelial cells - Better stabilization on the irregular cornea		- Hard maintaining a balance/stability connection between both lenses - Development of new vasculature - Expensive	- Excessive movement → Bubbles or debris, degrading the optical quality and changing cornea metabolism - Hypoxia led to corneal edema

RGP, rigid gas permeable.