★Types of contact lenses:-
These arrangements better endured by eye as more antacid or corrosive arrangements causes hazing impact.
1-Hard contact lenses:-
Made of rigid plastic resin polymethylmethacrylate.
Impermeable to oxygen and moisture.
2-Soft contact lenses:-
Made of hydrophilic transparent plastic,hydroxyethylmethacrylate.
Contain 30-80% water so are permeable to oxygen.
Have two types: daily wear and extended wear.
★Advantages of soft contact lenses:-
(a)Worn for longer periods.
(b)Do not dislodge easily.
★Disadvantages of soft contact lenses:-
Have shorter life span and the wearer must ensure that the lenses do not dry out.
3-Rigid gas permeable (RGP):-
Take the benefits of both delicate and hard focal points ,they are hydrophobic and oxygen permeable.Take the upsides of both delicate and hard focal points ,they are hydrophobic and oxygen penetrable.
★Advantages of hard contact lenses and RGP lenses:-
(a) Strength durability.
(b) Resistant to absorption of medications and environmental contaminants.
(c) Visual accuracy.
★Disadvantages of hard contact lenses and RGP lenses:-
(a) Require adjustment period of the wearer.
(b)More easily dislodged from the eye.
★Products for hard contact lenses:-
(A)Cleaners :to remove lipid and protein depris.
Formulation:-
Surface -active agent :to enable gentle friction with fingertips and antibacterial-fast acting: benzalkonium chloride.
(B) Rinsing and storage solutions:-
Facilitate lens hydration.
Inactivation of microbial defilement and keep the focal point from drying out.
Formulation:-
0.9%NaCl(isotonic)and antibacterial-3%hydrogen peroxide for 30min followed by inactivation with sodium pyruvate.
★Products for soft contact lenses:-
(A) Rinsing and storage solutions:-
For cleaning, microbial inactivation and hydration.
Formulation:-
Surface-active agent and antimicrobial:(0.01%benzalkonium chloride+0.1%sodium edetate;EDTA).
(B) Wetting solutions:-
To achieve rapid wetting by the lachrymal fluid and promote comfort.
Facilitate insertion of the lens.
(C)Buffering solutions:-
Hypromellose eye drops B.P.C.
Buffered to pH8.4 To 8.6 with boric acid and borax.