Lens Materials and Index of Refraction

Index of refraction:  the index of refraction as it pertains to optical lenses, discusses how efficiently a lens material can refract or bend light.  The higher the index of the material the more efficient it is as a refractive medium.  As the result of a material’s increased efficiency, a lens constructed of a higher index material can be made thinner and still achieve the same optical effect of a thicker 1.49 plastic lens.

1.49 Plastic:  Standard optical material.  Mainly used for prescriptions +/-3.00D.  These should be coated with a scratch resistant coating for maximum durability.  Anti-reflection-coating is recommended, especially if used for night driving or in an environment where fluorescent lighting is in use.  1.49 Plastic lenses are available in clear, Transitions and polarized.

1.56 Mid-index Plastic:  Used much in the same fashion as 1.49 plastic.  This lens material finds itself to be just slightly thinner than regular plastic and moderately lighter.  Used for prescriptions ranging from 0.00D. to +/-3.00D.; when weight and thickness are a concern as a result of frame size selection.  Much like 1.49 plastic, scratch resistant and anti-reflection coatings are highly recommended.

Polycarbonate:  This is the lightest lens material available on the market (in fact 20% thinner and 30% lighter than regular plastic), making it a comfortable choice for people who are looking for the most light-weight glasses.  Polycarbonate lenses are also 100% UV protectant in a clear state.

Polycarbonate is also the material of choice for impact resistance.  Polycarbonate is actually a softer material, allowing it to flex as oppose to shatter under intense impact.  For this reason, it is used in about 90% of all CSA approved prescription safety eyewear.  The material quality of polycarbonate also makes it the material of choice for semi-rimless eyewear and drill mounted (rimless eyewear).  Due to its flexible nature, it is less likely to chip or crack on the areas of the lens that are exposed or in contact with the mounting hardware.

Though polycarbonate has great impact and chip resistant qualities, it is inherently a softer lens material (it will scratch more easily than other optical plastics).  It is imperative to apply a high quality scratch protection to these lenses in order to lengthen their lifespan.

It is also fairly important to apply an anti-reflection coating to polycarbonate lenses.  Approximately 10% of the population is unable to adapt to polycarbonate lenses due to high amounts of chromatic aberration (distortion in a lens that breaks down light into its component colors).  Chromatic aberration is reported by a patient when he or she experiences a rainbow effect in the periphery of the lens.  Chromatic aberration can be improved for some through the application of an anti-reflection coating.  Polycarbonate lenses are available in clear, Transitions and polarized.

1.6 Hi-index Plastic:  This lens material is a great option for people with moderately strong prescriptions.  It is up to 25% thinner than regular plastic and provides 100% UV protection in its naturally clear state.  We recommend using this material for prescriptions ranging from +/-3.50D. to +/-6.50D.-pending the size and style of frame chosen.  This material is also a good choice for semi-rimless and drill mounted frames as it is less prone to chipping or cracking than regular plastic.  Due to its inherent moderate chromatic aberration, it is highly recommended to apply an anti-reflection coating to this material in order to maximize visual performance and optical clarity.  1.6 hi-index lenses are available in clear, Transitions and polarized.

1.67 Hi-index Plastic:  This lens material is a great option for people with strong prescriptions.  It is up to 33% thinner than regular plastic and provides 100% UV protection in its naturally clear state.  We recommend using this material for prescriptions ranging from +/-5.00D. to +/-8.00D.; pending the size and style of the frame chosen.  This material is also a good choice for semi-rimless and drill mounted frames as it is less prone to chipping and cracking than regular plastic.  Due to its inherently noticeable chromatic aberration, it is highly recommended to apply an anti-reflection coating to this material in order to maximize visual performance and optical clarity.  Truly, this material should never be worn without an anti-reflection coating-though it can be offered that way.  1.67 hi-index lenses are available in clear, Transitions and polarized.

1.74 Ultra Hi-index Plastic:  This lens material is the optimum choice for people with very strong prescriptions.  We recommend using this material when your prescription ranges from +/-6.50D. to +/-15.00D.  1.74 hi-index lenses are very efficient at bending light, resulting in a lens that is approximately 50% thinner than its regular plastic counterpart ground to the same prescription.  This material is also a good choice for semi-rimless and drill mounted frames as it is less prone to chipping or cracking than regular plastic.  Though fantastically thin and comfortable, like all hi-index lenses, this material suffers from chromatic aberration-and in very strong prescriptions, spherical distortion.  To maximize quality of vision, this material comes standard with an anti-refelction coating.