Optical lenses have played an extremely important role in the development of human history. With the improvement of science and technology, especially the rapid development of polymer materials, inorganic optical glass lenses have been gradually replaced by polymer resin lenses with excellent optical performance and light weight due to their heavy quality and wearing safety. In addition, as lens wearers tend to be younger and pursue aesthetics, the lightness of lenses has been put forward with higher requirements, the centre thickness of resin lenses is required to be processed thinner, and the refractive index of lenses is required to be higher.
In order to give you a better understanding of high index lenses, in this article we will focus on high index lenses before and after: what they are, the types of high index lenses available, which high index lens is best for you and their respective advantages and disadvantages.
What are High Index Lenses?
High index lenses are lenses that are thinner and lighter than regular lenses. They are often used to correct higher levels of nearsightedness or farsightedness because they reduce the thickness and weight of the lens while providing better aesthetics. High index lenses are stronger and can be used in half-rim and rimless glasses, and most high index lenses are aspheric, which makes them thinner and largely eliminates the ‘bug-eye’ look.
What is a Refractive Index?
The refractive index of a lens is the ability of a lens to refract light and is an important parameter of the lens material. Generally speaking, the higher the refractive index of a lens, the better its optical properties and the thinner the lens will be. A lens with a high refractive index will have thinner edges for the same prescription, making the lens lighter and more aesthetically pleasing, as well as providing better vision.
The refractive index of a lens is usually expressed as a number, such as 1.50, 1.56, 1.61, 1.67, 1.74, etc. These numbers indicate the material of the lens. These numbers represent the refractive index of the lens material, and different materials have different refractive indices. The refractive index of common resin lenses is usually around 1.50, while the refractive index of high refractive index glass lenses can reach over 1.70.
What are High Index Lenses Made of?
High-index glasses lenses are made from plastics that are specially manufactured to bend light more effectively than regular lenses because the plastic used to manufacture high-index lenses are usually denser than normal plastic. These lenses use less material because they can be cut more thinly than regular lenses.
The following are the most common materials used in eyeglass lenses from thickest to thinnest.
- CR39 (standard) plastic – 1.50(1.49/1.499)
- Trivex – 1.53
- Mid-index plastic(NK55, imported from Japan) – 1.56(1.57)
- Polycarbonate – 1.59
- 1.60 high-index plastic(MR-8, imported from Korea) – 1.60(1.61)
- 1.67 high index plastic(MR-7, imported from Korea) – 1.67
- 1.74 high-index plastic(MR-174, imported from Korea) – 1.74
Types of High Index Lenses
High-index lenses can be categorised by different gradients, and have their index number.
-
1.61 High Index Lenses
1.61 high index lens is a relatively high index lens for mild to moderate myopia or hyperopia correction. It is about 20% thinner lighter than the standard index lens (1.50). It is designed for people with high prescription between +3.00 and -4.00. However, the lighter material makes the lenses more comfortable and minimises the bulkiness of thicker lenses. This also means they fit most styles of spectacle frames.
-
1.67 High Index Lenses
The refractive index of is taller than 1.61 lens and is suitable for moderate to severe myopia or hyperopia correction. It is thinner and lighter than 1.61 lenses, and for those who require more advanced correction, the thinner lenses are easier to match with any type of frame, providing better vision and aesthetics. 1.67 lenses are 33% thinner than 1.50 lenses, which enhances vision for those who require between +4.00 and -6.00 diopters.
-
1.74 High Index Lenses
1.74 high index lens is one of the highest high index lenses available for severe to very severe myopia or hyperopia correction. It is the thinnest and lightest high index option, 45% thinner than standard lenses. This significantly reduces the weight of the glasses and provides ultimate comfort without compromising visual clarity. This index lens is significantly thinner and is suitable for all spectacle frames and for people with a prescription over -6.00.
-
1.90 High Index Lenses
1.90 high index lenses are usually made of glass material. Glass lenses have a higher refractive index than plastic lenses and can be made thinner for the same amount of power.1.90 high index lenses are ultra-thin, lightweight lenses designed for strength prescriptions. They offer excellent clarity and comfort, reduced distortion, and enhanced durability. However, glass lenses are also heavier and more fragile.
The Advantages and Disadvantages of High Index Lenses
Advantages
-
Thinner and Lighter
High index lenses tend to be aspheric in design, producing thinner lenses that do not make the frames appear too heavy, improving the aesthetics when worn. The thinner lenses also reduce the weight of the lenses, providing a more comfortable wearing experience, especially for those who need to wear glasses all day long.
-
Fits Most Frames
High index lenses are usually lighter and thinner and can fit many types of frames. They can also be applied to tinted lenses, polarised lenses and transition lenses to suit your style.
-
Comfortable to Wear
These ultra thinner, lighter lenses are not heavy, and the glasses are less likely to slide down your face.
Disadvanatges
-
Cost
High index lenses are usually more expensive than regular plastic lenses because they are more expensive to manufacture and use, and refractive index is higher, the amount is more expensive, 1.74 high index lenses price is the most.
-
Easy to reflections
High index lenses may add to the problem of reflections and affect visual comfort. Each type of lens blocks some light from entering the eye and reflects it away. While ordinary plastic or glass lenses reflect about 8% of light, high index spectacle lenses reflect up to 50% more light than ordinary glass or plastic lenses. This reflection can make night driving difficult.
Are High Index Lenses Worth it?
To determine are high index lenses worth it, there are a few things to consider, the most important of which is the degree. If you have a high prescription, we usually recommend high index lenses to reduce thickness and weight and increase comfort, 1.67 or 1.74 lens can be considered. Of course, budget is also a part to consider, as high index lenses are usually more expensive, so if you want value for money 1.61 index lens is a good choice!
