What are High-Index Lenses?

High-index lenses are made of a special plastic material that allows your eyeglasses to be thinner and lighter because they bend light more efficiently. Many people enjoy using high-index lenses because they look better cosmetically and feel more comfortable. 

There are several types of eyeglass lenses available, listed here in order of thickest to thinnest:

• CR-39 plastic is often referred to as standard, regular, or plastic lenses. Some features of CR-39 include low cost and excellent optical quality. However, the lenses tend to be thick with higher prescriptions.
• Polycarbonate is the go-to lens for children’s eyewear, sports goggles, and safety glasses because of its high impact resistance. One drawback is that polycarbonate tends to have more chromatic aberrations than any other lens material, which means poorer visual quality. Although many people do well with polycarbonate lenses, some have trouble adapting to them because of the visual quality.
• Trivex is similar to polycarbonate in that it is also incredibly impact-resistant. Other benefits of Trivex include fewer chromatic aberrations than polycarbonate, and it is the lightest lens material.
• High index is the thinnest eyeglass lens available, in addition to being lightweight. Because these lenses tend to reflect more light, most opticians and eye doctors recommend adding an anti-reflective coating to reduce glare.

What Vision Problems Do High-Index Lenses Correct?

High-index lenses correct all types of refractive errors, including myopia (nearsightedness), hyperopia (farsightedness), and astigmatism. A reading prescription that corrects presbyopia (age-related farsightedness) can also be added, such as in a bifocal or progressive lens.

Farsighted lenses are thicker in the center and thinner on the edges. Nearsighted lenses are thicker on the edges and thinner in the center. As the prescription increases, the thickness is more pronounced.

What Types of High-index Lenses Are Available?

There are a variety of high-index lenses you can select. The higher the number (refractive index), the thinner the lens. Generally, the higher your prescription, the higher the index you may need. For reference, standard plastic lenses have a refractive index of 1.50.

When you are looking at your eyeglass prescription, a plus (+) sign in the “sphere” section indicates a farsighted correction, while a minus (-) sign indicates a nearsighted correction. The higher this number, the stronger your prescription. The number in the “cyl” section indicates the strength of your astigmatism correction. If there is no number here, you do not have astigmatism.

1.61 Index

These lenses are about 25% thinner than CR-39 lenses. A 1.60 high-index lens is suitable for prescriptions around +3.00/-6.00 or less, and astigmatism correction of -3.00 or less.

1.67 Index 

These lenses are about 30% thinner than CR-39 lenses. A 1.67 lens is suitable for prescriptions under +5.00/-8.00, and astigmatism correction between -3.00 and -4.00.

1.74 Index 

These lenses are at least 35% thinner than CR-39 lenses. They are the thinnest high-index lenses. This lens is suitable for prescriptions above +5.00/-8.00, and astigmatism correction between -4.00 and -6.00.

Pros and Cons of High-Index Lenses

There are many benefits to wearing high-index lenses. Whether high-index lenses are the best choice for you depends on a few things, including your prescription, the type of frame you select, and how sensitive your eyes are. Some people do better with certain lens materials than others.

Some benefits include:

• Lightweight 
• Thinnest lenses available
• 100% UV protection
• Excellent durability
• Provides crisp vision and good peripheral vision (when paired with an aspheric design)
• Good for strong prescriptions
• Suitable for semi-rimless or thinner eyeglass frames (high-index lenses have thinner edges)
• Better cosmetic appeal
• Eyes appear less magnified for farsighted prescriptions and less minified for nearsighted prescriptions

Some drawbacks include:

• Higher cost than other lens materials 
• Not as lightweight as polycarbonate or Trivex
• Not as impact resistant as polycarbonate or Trivex
• Not suitable for drill-mount (rimless) frames (Trivex and polycarbonate are less likely to crack, making them a better option for rimless styles)
• Reflects more light, which can be reduced by anti-reflective coating

High-Index Lenses vs. Regular Plastic Lenses

One of the most significant differences is lens thickness. Regular CR-39 plastic tends to be quite a bit thicker than high-index lenses. CR-39 can be 25% to 50% thicker, depending on the type of high-index and the prescription. This is why regular plastic lenses are better for lower prescriptions, around +2.00/-3.00 or less.

The optical quality is better in CR-39 lenses. High-index lenses can reflect up to 50% more light than regular plastic lenses. Many optical retailers often include anti-reflective coatings with high-index lenses to reduce glare.

Types of High-Index Eyeglasses

High-index lenses can be combined with many other features and lens types. Some of those options include the following:

Aspheric Lenses

Most high-index lenses are aspheric in design, which means the lens is flatter. Aspheric lenses are slimmer and help to minimize the edge thickness, particularly on high myopic prescriptions. Aspheric high-index lenses also help minimize the magnification caused by high hyperopic prescriptions, otherwise known as the “bug-eyed” look. 

Photochromic Lenses

Photochromic lenses are clear indoors and turn dark when you go outside. They are convenient if you do not want to carry a pair of clear eyeglasses and another pair of sunglasses. Although they block 100% of UV rays and reduce glare, some people find that photochromic lenses do not turn dark enough while inside the car or on an overcast day.

Polarized Lenses

Polarized filters reduce glare off horizontal surfaces, such as road surfaces and water. They are often added to sunglass lenses to improve contrast and quality of vision. Polarized sunglasses are excellent for people who spend lots of time outdoors or are very sensitive to light.

Bifocal Lenses

Bifocals are suitable for those who are presbyopic and need reading correction. The top of the lens contains the distance prescription, while the lined segment on the bottom half of the lens includes the reading prescription.

Progressive Lenses

Progressive glasses provide distance, intermediate, and near correction. Unlike bifocal glasses, progressives do not have a line segment. Some people prefer progressives for cosmetic reasons, while others find that progressives are more suitable for computer use versus bifocals.

High-Definition Lenses (HD lenses)

HD lenses, also known as digital lenses, are highly customized lenses that deliver higher quality vision than traditional lenses. These lenses use digital computer technology to correct a wide range of vision problems, resulting in sharper and brighter vision.