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Soft Contact Lens Material.pptx
Soft contact lenses are made of hydroxyethyl methacrylate (HEMA), which was developed by Wichterle and Lim. HEMA contains a polar OH group that allows water to bind. Contact lenses can have water contents ranging from 38-80%, with lower water content lenses being more stable and easier to handle, and higher water content lenses having greater oxygen permeability but being less stable. Lenses can also be ionic or non-ionic, with ionic lenses being more deposit-prone but better wettable, and non-ionic lenses being less deposit-prone but less wettable. The FDA classifies soft contact lenses into four groups based on water content and ionicity. A lens's Dk, or
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Soft Contact Lens Material.pptx
- 1. Soft Contact LensMaterial By Babli Sharma B.Optom, M.Optom
- 2. Hydroxyethyl-methacrylate PHEMA OWichterle and D Lim A polar OH group to which water lipole binds 38% water content Are soft and pliable Large lens diameters New generation-soft material-improved PHEMA combination of other polymers 2-3
- 3. Physical Properties Water content Rangesfrom 38%-80% >40% are low water content Dk range 5-8 Low oxygen permeability Low water content lenses are stable, Easier to handle More wettable 40-55% are mid water content Dk range 7- 19 >55% are high water content Dk range 18- 28 Higher the water content greater the oxygen permeability Less stable Fragile More deposit prone Less dimension stability Thicker due to low refractive index
- 4. Ionicity Ionicity Ionic Net Negative charge More proneto deposits Better wettability Nonionic No net surface charge Less deposit prone Less wettable
- 5. FDA Classification Groups In 1986 US food and drug administration classified hydrogel contact lenses into 4 groups • Non ionic Low water content 38-50% Group -1 • Non-ionic High water content 51-80% Group-2 • Ionic Low water content 38-50% Group-3 • Ionic High water content 51-80% Group-4
- 6. Soft materials andDk-depends on Water content if higher increases Dk Material chemistry If pH is acidic it reduces water content Hyper tonicity reduces water content
- 7.