Chapter 4: LENS OPTIONS

a lens material indicates how much the material will refract or bend light as it enters the material from air, by comparing the speed of light in a given material to the speed of light in air.

describes the density of a lens material by comparing its density to the density of water.

the higher the index of a lens material, the higher the chromatic aberration, and the lower the Abbe value.

• The reflectance of the material describes the percentage of incident light reflected from a highly polished surface of that material and is calculated from the refractive index of a material. When light hits a lens surface in air normally, the percentage of light reflected at each surface is given by:
• R = (n - 1)2/(n + 1)2 * 100%
• Thus a material of refractive index 1.5, has a reflectance of
• (0.5/2.5)2*100 = 4% per surface

The transmittance of a lens material describes the amount of light (usually specified for a given waveband) that will pass through that material.

• Pros:
•    Superior optics
•    Stable material
•    Scratch resistant
• Cons:
•    Does not accept tint
•    Not impact resistant
•    Heavy

• Pros:
•    Lighter than glass
•    Readily tint-able
•    Less likely to fog
• Cons:
•    Susceptible to scratching (correctable by coating)
•    Lower index of refraction makes it less suitable for higher powered prescriptions

• Pros:
•    Thinner and lighter than glass and plastic
•   Highly impact resistant (used for safety glasses)
•    Inherent UV protection
• Cons:
•    Poor optical quality
•    Susceptible to scratching (correctable by coating)
•    Susceptible to stress fractures in drill mounts
•    Does not readily accept tint

• Pros:
•    Thinner and lighter than glass and plastic
•    Better optical quality than polycarbonate
• Cons:
•    Susceptible to scratching (correctable by coating)
•    Susceptible to backside and inner-surface reflections (correctable with AR)

• Pros:
•    Impact resistance of polycarbonate
•    Better optical quality than polycarbonate
•    Tint-able
•    Lightest material on the market
•    Inherent UV protection
•    High tensile strength (ideal for drill mounts)
• Cons:
•    Susceptible to scratching (correctable by coating)

• Reduces glare by 99%
• Eye fatigue, Itchy eyes
• Reduces glare: Driving, Computer (Phone/tablet), Artificial light reduces glare
• Makes lenses appear thinner
• UV, scratch

lens with a characteristic of changing state from clear to sunglass dark when exposed to light

• Transition lenses were created by PPG Industries
• Transitions lenses use a technology called imbibing to place the photochromic dye photosol a few microns below the front surface of the lens.

Photo Grey Extra and Photo Brown Extra are the original glass versions of a photochromic lens.

• • Flat Top – 25mm, 28mm, 35mm, 45mm, 7x28mm, 8x35mm, Double D 28mm, Double D 35mm, Quadrifocal 28mm
• • Curved Top – 28mm
• • Round – Achromat, Kryptok, Ultex, 22mm, 25mm, Double Round
• • Panoptik
• • Ribbon
• • Executive – Bifocal, Trifocal, ED Trifocal

or bicentric grinding, is a method of correcting vertical imbalance for patients with anisometropia.