Properties of contact lens mats Flashcards
(12 cards)
Density
defined by mass or volume
higher density heavier lens therefore lens may not center properly
in case of prism ballast may be beneficial
Refractive index (RI)
required refracive power of lens directly related to RI and determines thickness and curvature of lens
thicker lens = lower Dk
increased RI = thinner lens = increased Dk
Optical transmission
ratio of light that passes through material as percentage
should be 90+
Dimentional stability
High water content lenses will change durring wear
ability to rehyderate important to dim sta
Surface properties
wettability
adheasive - cohesive forces acting on a lens surface
C lens allow statain complete wetting allow a thick coverage of tear film, smooth recovery tear layer after eye closure and good VA
Water content
higher the water content, the more comfy the c lens is but there is a decrease in stability of the material
Mechanical properties
tensile strength
tear strenght
modulus of regiditiy
Oxygen permiability
Increased water content leads to increased oxygen permiability
Ocular compatability
Contact lenses are biocompatible with the ocular surface -
they are non toxic and well tolerated by ocular tissue
* The most obvious clinical manifestation of ocular
incompatibility is spoliation
* Clinical manifestations include protein, make up, microbial
spoliation, calcium…..
Toxicity and chemical stability
can cause accumulation of metabolic by product in anterior cornesl layers
can result in limbal keratitis, peripheral corneal infiltrtes and keratic precipitates
Quality of material
medical devices adn must custom fit
should be infected durring manafacturing processes and pre fitting
Methods of ease of sterilisation
done using autoclaver
