Essential Contact Lens terms Flashcards
What are Soft contact lenses, and what material are they made of?
SCL are lenses that cover the cornea and extend just beyond the limbus.
They are 13-15mm in diameter.
they are made of flexible hydrogel material (either conventional hydrogel or silicon hydrogel (SiH)
Flex to take up the shape of the cornea.
What are Rigid Gas Permeable lenses (RGP), and what material are they made of?
Corneal RGPs are 9-10mm in diamter. They are made of ma material capable of transmitting Oxygen. Rigid material with limited flexibility, which traps a layer of tears behind the lens.
The original rigid lenses were made from polymethyl methacrylate (PMMA) which did not let any oxygen pass through the material. It is now referred to as ‘hard’ lenses
Corneo-scleral (14-15mm) and semi-scleral (15-18mm) rigid lenses- larger diameter lenses made of RGP materials which cover the cornea and rest on the conjunctiva just beyond the limbus. Useful for fitting more complex eyes.
scleral lenses - large (~22-14mm diameter) rigid lenses made of GP material (or sometimes PMMA) that vault over the cornea and gently rest on the conjuctiva beneath the lids useful for fitting more complex eyes.
What does it mean by Lens replacement?
Depending on the brand, soft lenses are replaced monthly, fortnightly or daily.
RGPs and customised, complex lenses are genrally replaced every 6-24 months
