This post was most recently updated on February 29th, 2020
Whether this is your first time getting prescription glasses, or you have worn them all your life, there is a lot to learn about the materials of your lenses, the coatings that can be applied, and your prescription. It is good to be informed so that you and your eye doctor can work together to find the right solution for you. Here is some information to get you started as you learn about your prescription and lenses.
Lens Materials
The lenses of your prescription glasses can vary in material depending on what you and your doctor decide is best for your situation. There are many different materials to choose from and each one serves a different purpose.
Glass lenses are the most classic option available. At one time, all glasses were made from glass. They tend to be the hardest material and are not as prone to scratching. These lenses offer the clearest vision, but there are some major drawbacks. Glasses made from glass are much heavier than their plastic counterparts and they can break much easier. Many eye doctors worry about eye injury due to breaking glass. As a result, glass lenses are not commonly used anymore, although they are still available.
CR-39 Plastic lenses were invented over 70 years ago, but are still widely used today. The material is one of the cheapest to fabricate, allowing these savings to be passed to the customer. CR-39, or Columbia Resin 39, is much lighter than glass lenses making them much more practical for everyday wear. This material provides very clear vision as well, nearly rivaling that of glass.
Polycarbonate lenses are one of the strongest on the market today. They have been around for around 50 years, and have been widely used in safety glasses. However, their strong properties have also made them an ideal material for glasses that might see a bit more wear and tear. They are great for children’s glasses, athletes, or those working in warehouse or construction settings.
Trivex is a material that is similar to polycarbonate but much lighter. It is a new material and has only been in use since 2001. It offers the clearest vision next to glass and CR-39 plastic while being 100% UV resistant and the lightest material on the market.
High-index plastics, while not offering vision as clear as that of other materials, nonetheless has benefits that would make it a great choice. These are the thinnest lenses on the market and also are effective at blocking UV light. They are very lightweight and tend to be less expensive than other materials.
Tribrid lenses are one of the newest lens materials on the market today. This material is thin, clear, blocks 100% UV radiation, and is impact resistant. However, it is less widely available, and may not be an option for every lens type.
Understanding Abbe Value
One number that may be helpful to be familiar with is the Abbe value. This number describes how well a particular material is able to disperse light through the lens. The higher the number, the clearer the material. Materials, such as glass, which have a high Abbe number will have fewer visual disturbances such as halos. Although the Abbe value should be a factor when deciding which type of material to use, it is not the only consideration as many materials with a lower Abbe value can still provide clear vision. Crown glass, with an Abbe number of 59, has the highest number, while polycarbonate has the lowest lumber of 30.
Coatings
When understanding different coatings, it is important to remember that not every coating is compatible with every lens material, and not every coating is needed. Make sure to discuss with your doctor which combination of material and coating is best for you and your unique situation. Here are a few of the most common treatments.
Scratch-Resistant Coating
A scratch-resistant coating is an excellent choice for anyone needing extra protection from scratches and other damages. Although it is not possible to completely prevent scratches, this can add the boost that is needed to keep glasses in good condition. Some materials already contain anti-scratch coatings such as polycarbonate, Trivex, and some high-index lenses. Be sure to ask whether the coating is included or should be added. Almost all materials are compatible with this coating.
Anti-Reflective Coating
Anti-reflective coatings are some of the most recommended coatings. They are especially important for materials that have a lower Abbe Value, such as polycarbonate or high-index lenses. These coatings help to take away the glare from surrounding lights and completely eliminate reflections in the glass. This has many different benefits. This type of coating creates the clearest vision possible for the patient, while also making it easier for other people to see the patient’s eyes. This type of coating is especially important for individuals who frequently drive at night, and for those who have to do up close or intricate work.
Anti-Fog Coating
Although patients in some areas may not struggle with fogging glasses, those who live in colder temperatures may have this problem. Fog can form on glasses when the individual comes from cold temperatures outside to warmer temperatures inside. It can even happen when the patient is trying to enjoy a nice hot cup of coffee or tea. The temporary covering that occurs can be embarrassing and dangerous. This coating is extremely important for those who work in emergency services, or who drive for a living as even a little bit of fog can severely impair vision right when it is needed most. Most materials, including plastic, photochromic, and polycarbonate are compatible with anti-fog coatings.
Ultraviolet Blocking Coatings
Some materials, such as polycarbonate and Trivex already have 100% UV blocking properties. In such cases, additional coatings for UV rays are unnecessary. However, for all other materials, it is prudent to protect the eyes by adding this particular coating. UV rays can be incredibly damaging to the eyes. It is important to note that this treatment is just as effective as the protection that sunglasses provide, but sunglasses may still be necessary for those with a sensitivity to light.
Cosmetic Coatings
There are certain coatings that can also be added for cosmetic reasons. These include tinted coatings that can add color to the lens without altering the clarity of vision, or mirror coatings which have the same cosmetic effect as sunglasses, keeping the eyes hidden. Tinted lenses have also begun to be used for individuals who spend a lot of time on the computer and have developed Computer Vision Syndrome. It may help to reduce eye strain, but these options should always be discussed with a doctor.
Types of Glasses Prescriptions
There are four basic types of glasses prescriptions. The choice of which lens to get will depend on whether the patient is nearsighted, farsighted, or a combination of both. The basic types are single, bifocal, trifocal, and progressive.
Single Vision Lenses
Single vision lenses are made for individuals who need help with either only long-distance vision, or only up-close vision. For example, an individual who is near-sighted will require a prescription to help with seeing far away objects. This would also be the category for glasses that are worn purely for cosmetic reasons or to protect from particles, wind, or chemicals. Reading glasses with one prescription are also classified as single vision.
Bifocal Lenses
Bifocal lenses feature two different prescriptions: one for distance vision, and the other for close up vision. In this type of glasses, the lens is divided into two distinct sections. The top section has a prescription for faraway objects, and the bottom section is for any activity that is up close such as reading or looking at a computer. Individuals with bifocals simply adjust their vision as needed. For some, bifocals are not ideal. Head position may have to be adjusted while using the upper and lower portions of the lens and can cause neck pain. Also, the constant adjusting from one to the other can cause headaches and dizziness. In addition, most people find the appearance of bifocals to be aging or generally unattractive. However, bifocals may be the perfect option for patients who have developed presbyopia.
Trifocal Lenses
Trifocals, as the name suggests, are lenses that have three different regions, allowing for the patient to see at a far distance, close up, and in between. These are especially helpful for patients who have developed an extreme version of presbyopia and need help at every distance.
Progressive Lenses
Progressive lenses are the newest in presbyopia technology. For many people, they replace their multifocal lenses while still helping them to see well at any distance. Progressive lenses provide the same “three zone” sections for distance, near, and intermediate vision, but without the visible lines that are in trifocals. Instead, there is a smooth transition between each of the zones, increasing the aesthetics of the lens as well as the function. There are many benefits to this type of lens. Instead of only three separate powers, there are many different strengths combined into one lens. This “progressive” design allows for the individual to see at many different distances and eliminates the eye strain and headaches that may come from constantly adjusting from one half of the glasses to the other. Not only this, since bifocals and trifocals are often associated with old age, this type of lens can make the wearer feel and look much younger.
Photochromic Lenses
Photochromic lenses are a type of lens that adjusts depending on how much light is in the environment. These lenses become darker when the individual goes outside into the sunlight but will adjust back to a clear color when the individual goes back indoors. UV rays cause the particles in the photochromic lenses to react and makes them darken. In any environment that is free from UV rays, the lens will remain clear. These are great options for anyone who wants added protection from these harmful rays, and many parents are choosing them for their children.
Reading Your Prescription
Those who have not been to optometry school may be confused when they see the many different elements of their eyeglasses prescription. However, it is possible to learn to read the prescription without getting a degree. The prescription that the doctor writes will most likely indicate the OD, OS, and OU. These simply indicate which eye is being referenced. OD (oculus dexter) refers to the right eye, while OS (oculus sinister) refers to the left. OU (oculus uterque) refers to both eyes.
Lens power is indicated in the section labeled “Sphere” or SPH. The power of a lens is measured using diopters. The higher the number, the higher the power of the prescription. If the number has a minus sign, this indicates nearsightedness, while a plus sign indicates farsightedness.
The Cylinder or CYL sections contain information related to astigmatism. This may or may not have anything written in it, depending on whether the patient has any astigmatism. This indicates the strength of correction that certain sections or meridians of the eye need to correct astigmatism. The axis indicates the location of the lens where the astigmatism correction needs to be, while the “Add” section indicates whether an additional power is needed at the bottom for presbyopia. Finally, the prism is a rarely filled out section of the prescription that indicates any corrections that are needed for eye alignment. If you have any questions regarding your prescription, be sure to ask your eye doctor.
Expiration Dates
Every eyeglass prescription will contain an expiration date. This is important because eyes change over time and wearing a prescription that is not correct for the eyes can cause discomfort such as headaches, blurry vision from too weak of a prescription, or symptoms of eye strain. A prescription is usually good for one to two years, after which a return visit to the doctor is needed for a new prescription. Both optometrists and optical companies must legally adhere to these expirations dates.
The world of prescription eyeglasses may seem complicated at first, but with a little exploration, it is easy to understand both the type of lens that your doctor has recommended and the various elements of the prescription. You should always talk to your doctor about any questions or concerns you have regarding your glasses.