The Different Types of Prescription Lenses
There are many different types of prescription lenses. How should you decide which type of prescription lens is best for you? Our guide will cover the types of prescription lenses, lens materials, and lens designs. In addition, many components can be added to lenses to improve light sensitivity, protect against UV, and prevent double vision.
Single-vision lenses are either glasses or contact lenses with a single power. The power can be set for distance or near but is used for viewing at only one distance. Distance single-vision lenses are often used for driving, while near single-vision lenses are used for reading. Keep in mind a single vision lens prescribed for a certain distance may cause blurry vision at other distances depending upon your age and the lens power.
Multifocal lenses are designed to provide you with vision at multiple distances. They are usually prescribed for patients over the age of 40 with a condition called presbyopia. There are several types of multifocal lenses, including progressives, no-line bifocals, bifocal, and trifocal lenses.
Progressive lenses are also called progressive addition lenses or PALs. Progressive lenses have distance vision at the top of the lenses, and the powers increase towards the reading distance at the bottom. PALs do not just have three separate distances but a multitude of different distances allowing the wearer to see at all ranges. For most patients, PALs are the most functional lens for everyday use. Progressive lenses can be further divided into older, conventional progressives, and new freeform lenses.
Progressive lenses for driving
Freeform progressives have many advantages over conventional progressive lenses. Freeform lenses are made digitally to achieve better optics. The software analyzes data, including one’s prescription, pantoscopic tilt, and frame fitting position to create a customized lens for each individual. The freeform design allows for many different types of lens designs by integrating surfaces. The lens optics are located on the back surface of the lens, putting them closer to the eye. This is called the keyhole effect and results in clearer vision. Freeform lenses are considered premium progressive lenses because they provide a wider field of view and less peripheral distortion.
Instead of using computer analytics to generate an optical design, conventional progressive lenses are produced using “pre-molded” templates, and the same design is used for every wearer. The lens optics are located on the front surface of the lens, reducing the field of vision. Conventional PALs are less customized and do not consider as many patient-specific factors. The results are a reduction in optical quality, increased distortion, and less visual clarity for the patient.
A no-line bifocal is like a lined bifocal; it is composed of two distances, distance and near. However, it does not have a line to divide the powers, but there is a smooth transition from distance to near. The lens does not have an intermediate zone. A Shamir Duo lens is a type of no-line bifocal.
A lined bifocal lens has two separate powers, distance and near. They will work best for someone who needs glasses for driving, does not use a computer, and needs glasses for reading or sewing. The window will be set at the lid margin of the bottom lid for the best reading. If you need to see something at arm’s length, a bifocal is not ideal because the lenses do not include power for intermediate distances.
Trifocal lenses have three separate lens powers: distance, intermediate and near. Both the intermediate and near are delineated by two small windows. Trifocal lenses may be an option for those who cannot adapt to a progressive lens but need all three working distances. Trifocals have the addition of an intermediate segment for desktop computers, the dashboard on the car, and other tasks performed at arm’s length. Trifocals are available in two sizes, 7x28 or 8x35, with the latter having a larger size window.
Aspheric lenses correct for spherical aberration, which is an optical effect that causes light rays to focus at different points, causing blur. Aspheric lenses are smoother, flatter, thinner, and reduce distortion. Aspheric lenses are particularly beneficial for patients with high glasses prescriptions as the lenses will be thinner.
Spherical lenses can also be called singlets. The lens is a curved surface that causes light rays to either diverge or converge. Spherical lenses have a simpler design and are easier to produce. They may be adequate for patients with low prescriptions and little astigmatism.
Prism is a component added to glasses lenses to correct binocular vision disorders, lazy eyes, or double vision. Some patients may have been born with eye muscles that are out of alignment or may occur with age or disease. When a patient gets tired, the alignment may become worse, resulting in double vision. Prism is used to move the image to where the patient’s eye sees it. Your doctor will perform a series of tests to decide if your glasses need a prism.
Toric lenses are a specialty type of prescription contact lens for patients with astigmatism. Not all patients with astigmatism need a toric lens, but if you have greater or equal to -0.75 diopters, you will see better with a toric lens. A toric lens is a football-shaped power lens designed to match the football-shaped power of an eye with astigmatism. Toric lenses are designed to be thicker at the bottom or at the edges to maintain stability. If your vision changes significantly when you blink, the lens may be rotating in your eye. The greater the amount of astigmatism you have, the more you may notice blurry vision between blinks. A good toric contact lens provides stable vision and reduces the halo effect around letters and numbers.
High index is a type of thinner, lighter-weight lens material. A high-index lens bends light improving lens clarity. High-index lenses are made from plastics and are used in many products besides spectacle lenses. High-index lenses are recommended for patients with a prescription equal to or greater than -4.00D or +2.00D. High-index lenses are available in 1.60, 1.67, and 1.74, with the highest number being the highest index lens. A 1.74 is the best, thinnest, and lightest lens for a patient with a high prescription.
Polycarbonate is a strong, tough, and impact-resistant lens material. Polycarbonate is the standard material for kids and sports glasses, but may not be as optically clear as Trivex. Lenses are made of polycarbonate, so they do not shatter if a patient is hit in the face by an airbag or sports ball. UV is an inherent property of a polycarbonate lens.
1.56 refers to the len index of refraction or thickness of a lens. A 1.56-index lens is thinner and lighter than a standard 1.5-index lens.
Trivex lenses are clear, lightweight, and as impact-resistant as a polycarbonate lens. Visual clarity is greater through a Trivex lens when compared to a polycarbonate lens. Trivex lenses are ideal for children's glasses, sports glasses, and sunglasses.
CR-39 is a plastic polymer invented by PPG industries. CR-39 is the go to lens for individuals who have a low prescription and don’t need an impact resistant lens. CR-39 is optically the clearest with the least amount of aberrations. It is naturally scratch resistant and can be tinted easily but not as light or strong as Trivex.
Tinted Lenses/Lenses with Tint
Polarized lenses contain a polarizing film. Works great for sun protection, to reduce glare, and to enhance color. Images appear sharper and clearer through polarized lenses. Not all sunglasses are polarized. They are an upgrade for a tinted lens, which just makes the world appear darker. Those that enjoy water activities like boating or fishing or snow involving snow activities like skiing will benefit from polarized lenses.
View from a polarized lens
A tinted lens is a clear lens dipped in a tint to make the lens darker. Tints are available in many colors and darknesses, solid or gradient. Dark gray, dark amber, and green are the most common. Tints can be used to reduce sunlight to the eye or as a fashion statement.
View from a gray tinted lens
Therapeutic lenses such as F-41 may be beneficial for patients with a history of migraines, concussions, or other neurological problems. The rose-tinted lenses block certain wavelengths of blue light to reduce the intensity of light and improve one’s light sensitivity.
Light Responsive/Photochromic lenses
Photochromic lenses are a novel lens technology activated by UV light. With the newest technology, photochromic lenses are activated by both UV and visible light, allowing them to turn dark behind a car windshield such as Transitions® Xtra Active® . The lens will turn dark when exposed to sunlight and return to clear after a period of time indoors.
Which Prescription Lens Type is Right for You?
When determining what prescription lens type is right for you, you must consider the number value of your prescription, what types of activities you need your lenses for, and any special features that you desire from your lenses.
There are many different types of prescription lenses, lens materials, and lens features. With the advice of your eye doctor and our guide, you can decide which options are best for you. When you order your new prescription lenses, consider the written prescription for your eyes, what type of improvements in your vision you desire, your occupation and hobbies, and the lens features that may best improve your vision and the quality of your life!