Table 1.

A list of the polymers mainly employed to prepare therapeutic Contact Lenses (CLs). pHEMA: poly (2-hydroxyethyl methacrylate); PMMA: poly (methyl methacrylate).

Polymer	Properties
pHEMA	Biocompatible, but not biodegradable Hydrophilic properties, due to the presence of an –OH group Water-absorbing material When dry, it has the properties of hard organic glass; after the hydration, it becomes soft and flexible Generally display very poor mechanical properties Generally employed for soft CLs, which are fragile/less durable but very comfortable
PMMA	Rigid/poorly flexible High stability to UV and atmospheric agents Limited chemical and heat resistance Scarce permeability to oxygen Excellent light transmission Good mechanical and optical properties (e.g., transparency) Low water-absorbing capacity Generally used for rigid CLs, which are cheap and durable, but uncomfortable
Silicone/siloxane	Biocompatible, but not biodegradable Chemical inert (e.g., not readily attracked by oxygen) Resistance to water and oxidation Highly flexible Stability at both high and low temperatures Very high permeability to gases Generally employed for soft CLs, which are fragile/less durable but very comfortable