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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:
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High-index plastic lenses correct all types of refractive errors, including myopia (nearsightedness), hyperopia (farsightedness), and astigmatism. They are available as single vision lenses, or 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.
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 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.
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.
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.
These lenses are at least 35% thinner than CR-39 lenses. They are the thinnest high-index lenses. This lens is suitable for stronger prescriptions above +5.00/-8.00, and astigmatism correction between -4.00 and -6.00.
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:
Some drawbacks include:
High index lenses typically cost approximately $150 to $200 for single vision and $300 to $400 for progressives.
Speak with your optometrist, or an eye care specialist to find out if high-index glasses are your best option for prescription 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.
High-index lenses can be combined with many other features and lens types. Some of those options include the following:
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 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 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.
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 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.
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.
High-index lens material is a great option for stronger prescriptions, as they are thinner and lighter. However, polycarbonate are more impact resistant, making them a better option for sports, protective, and children's frames
High-index lenses do cost more than regular polycarbonate lenses. However, people with strong prescriptions will likely find the additional cost worth it, since high-index lenses are much thinner, lighter, and aesthetically pleasing.
High-index lenses are more expensive to manufacture and more difficult to grind, making them more expensive than other types such as polycarbonate.
It is possible that high-index lenses cause slight distortion in your peripheral vision due to their low Abbe value.
1.67 index lenses are suitable for prescriptions under +5.00/-8.00, and astigmatism correction between -3.00 and -4.00. 1.74 index lenses are the thinnest high-index lenses. This lens is suitable for stronger prescriptions above +5.00/-8.00, and astigmatism correction between -4.00 and -6.00.
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Coronis, Timothy. “Winning the High-Index Numbers Game.” 20/20, 15 July 2009, www.2020mag.com/article/winning-the-high-index-numbers-game.
Whitney, Dick. “Does Material Abbe Value Influence Your Patient's Vision?” 20/20, 14 Sept. 2015, www.2020mag.com/article/does-material-abbe-value-influence-your-patients-vision.