If you are looking for thinner, lighter, and more attractive spectacle lenses and glasses, high-index lenses are the right choice.
If you have a strong prescription for short-sightedness, long-sightedness, or astigmatism, thin, lighter high-index lenses should be considered. In spite of how strong your prescription is, high-index lenses can make your spectacles noticeably slimmer, lighter and more attractive.
The majority of spectacle wearers are short-sighted, which requires corrective lenses that are thin in the center and thicker at the edges. The stronger the prescription, the thicker the edges.
Today’s fashionable frames are usually made of plastic or metal with thinner rims than the lenses.
The edges of the lenses are fully exposed in rimless mountings.
It is important to note that the lens edges are highly visible in either case, and thicker edges may detract from the appearance of your glasses.
High-index lenses vs. regular spectacle lenses
Your optician will determine the amount of light-bending ability (lens power) that is required to provide good vision on your spectacle prescription.
There is a noticeable difference between regular plastic lenses and high-index lenses when it comes to correcting nearsightedness.
It is important to note that refractive errors and the lens powers required to correct them are measured in units called diopters (D). If you are mildly shortsighted, your lens prescription might say -2.00 D. If you are highly myopic, it may say -8.00 D.
Longsighted individuals require “plus” (+) lenses, which are thicker in the center and thinner on the edges.
It is quite common for regular glass or plastic lenses for high levels of shortsightedness or longsightedness to be quite thick and heavy.
In recent years, manufacturers have created a variety of new “high-index” plastic lens materials that are more efficient at bending light.
As a result, high-index plastic lenses are both thinner and lighter than conventional glass or plastic lenses, since they require less material to correct the same amount of refractive error.
Advantages of high-index lenses
A high-index lens for shortsightedness has thinner edges than a conventional plastic lens with the same prescription power due to its ability to bend light more effectively.
Lenses made of high-index plastic are lighter than lenses made of conventional plastic, so they are more comfortable to wear. Thinner edges require less lens material, resulting in a lighter overall weight.
In addition to having thinner edges, high-index glass lenses are heavier than conventional glass, so they do not offer the same weight savings as plastic lenses.
Those with long-sighted prescriptions, which can be very heavy, will benefit greatly from lightweight lenses.
Aspheric lenses also have a slimmer, more attractive profile, reducing the magnified appearance that conventional lenses cause in strong longsighted prescriptions.
High-index lens choices
In terms of how efficiently they bend light, there are a variety of thin, lightweight high-index spectacle lenses available.
A spectacle lens’ ability to bend light is influenced by its refractive index, which is the ratio of the speed of light when it passes through air to the speed of light when it passes through the lens material.
The speed of light is reduced the more it is refracted as it passes through a lens material. It follows that lenses that are more efficient at bending light have a higher refractive index than lenses that are less efficient at bending light, and lenses made of materials with a higher refractive index are thinner.
The thinner a lens is, the higher its refractive index.
Plastic lenses have a refractive index of approximately 1.50, whereas glass lenses have a refractive index of 1.52.
High-index lenses are those that have a refractive index higher than glass or plastic.
Plastic lenses with high refractive indices are available in a variety of refractive indices between 1.53 and 1.74. Plastic lenses with a refractive indices of 1.70 or higher are typically at least 50% thinner than conventional plastic lenses.
As a general rule, the higher the index, the higher the cost of the lenses.
Depending on the strength of your prescription, you may be required to use high-index lenses. The highest index materials are used primarily for the strongest prescriptions.
You should ask your optician for high-index lenses if you desire them, but rely on his advice on which index to choose. Your optician will be able to explain which high-index lenses are most suitable for your needs and budget.
There are a number of lens designs and features that are available in high-index materials today, including progressive lenses and photochromic lenses. However, there are some exceptions, so ask your optician for more information.
High-index lenses benefit from AR coatings
All lens materials block some light from passing through them. This light is reflected back from the surface of the lens, causing distractions and reducing night vision clarity.
The conventional glass or plastic lens reflects about 8 percent of light that otherwise would reach the eye. The high-index lens reflects up to 50 percent of the light that otherwise would reach the eye.
A high-index lens should be coated with an anti-reflective coating (AR coating) for optimum vision and appearance. AR-coated high-index lenses transmit up to 99.5 percent of light to the eye.
Due to AR coating’s ability to virtually eliminate lens reflections, high-index lenses are virtually invisible, so others see your eyes and not your lenses.
As well, studies have shown that spectacle lenses with anti-reflective coatings provide better night vision with a reduced amount of glare.