Earlier, there were times, when thick glass wearers were teased by friends and subordinates. The thick spectacle lenses were uncomfortable to wear and being mostly in glass had a complaint of breakage. There was no concept of high Index lenses and the users felt very uncomfortable in wearing thicker glasses in earlier times. People who had such high prescriptions could not follow fashion trends. However, today lightweight eye lenses are available for people who need correction in their vision with high powers.
Refraction corrects most vision defects. When a refraction is done, light is bent as it passes through a lens. The more the light is bent, the stronger is the prescription. More light is bent if the prescription is higher but in case of high refractive index lenses, light refracted is more efficient than in case of traditional lenses. With the material being more efficient, less material is required to make a corrective lens.
Today with the technology changing, different materials are available to ensure comfortable vision. Thin lenses are now manufactured using different available materials. There is high refractive Plastic and glass material with good optical quality with Plastic material having advantage of lighter weight compared to glass. With a 1.6 or 1.7 Index, there is less curvature on the frame leading to a thinner lens. Plastic Lenses have various indices available with 1.6 Index spectacle lenses being most used. Whenever the manufacturer uses high index material for lenses, it’s density increases and lesser material is used to make lenses thereby making it thin. A lens with high Refractive Index is relatively thin. High power prescription are the ones where the user needs to use High Refractive Index for their spectacle lenses. Some lenses are used even for high Plus powers where a thinner centre helps in reducing the weight and thickness of the lens. Aspheric lenses are used for Plus power lenses. Most aspheric lenses are made in high index material.
However, these lenses are very reflective and cause problems for drivers. Some countries also do not allow its drivers to drive without antireflection lenses especially if they are using lenses with high Indices. Antireflection lenses reduce light reflection and help in ensuring the same of the driver while driving and improve the vision. They have a downside to them as well as they are more expensive and prone to scratches. A superior scratch resistant coating is required on the lenses to prevent scratches.
Most people who use high index lenses suffer from myopia. The lenses become thin when the refractive index used is high. Today, Ultra High Index lenses are used to high myopes. Users with prescriptions like +11.00/-11.00 can make use of these Ultra high index lenses for a thin and flat eyeglass. The cost of these is a lot more though. 1.9 Index Glass lenses along with 1.74 Plastic lenses are the thinnest index lenses. They are available at the lowest possible prices online.