Eyeglasses: What They Are, How They Work, Parts & Types (2024)

What are eyeglasses?

Eyeglasses are wearable lenses mounted in a frame you wear on your face so you can see better. They do that by correcting refractive errors (like nearsightedness) or other issues that make it hard for you to see properly. Corrective lenses in prescription and reading eyeglasses get their name from how they “correct” your eyesight. They compensate for what your eyes can’t do on their own so you can see clearly.

Eyeglasses (often known simply as “glasses” or “spectacles”) can help with a variety of vision issues. That includes difficulty seeing objects up close, far away or at varying distances. They can also help with distortions in your vision, age-related vision difficulties and eye alignment issues.

What do eyeglasses do?

Eyeglasses do for your eyes what a stepstool does for how high up you can reach. They help you use an ability that isn’t strong enough on its own.

When beams of light enter your eyes, they pass through the cornea and lens. The cornea and lens are supposed to bend light beams so they converge on the retina at just the right distance. When they do this correctly, your vision is clear and sharp.

But if you have a refractive error (either in one or both eyes), the affected eye(s) can’t bend beams of light correctly, making things look blurry and out of focus. That’s where eyeglasses come in. They add more bend to the light than your eyes can do on their own.

Eyeglasses can also help with double vision (diplopia) because of eye misalignment. When your eyes align correctly, your brain can seamlessly “fuse” input from both eyes into a single picture. When your eyes don’t align correctly, you get double vision because there are two competing pictures. Certain types of lenses can compensate for that.

What can eyeglasses help with?

There are four main types of refractive errors that eyeglasses can help:

• Nearsightedness (myopia). Objects close up are clear, but objects farther away are blurry.
• Farsightedness (hyperopia). Objects far away are clear, but objects close up are blurry.
• Tilted or distorted areas of vision (astigmatism). Your vision is blurry close up and far away. It can also cause visible “starburst” rays coming off lights (especially at night).
• Trouble focusing up close due to age (presbyopia).

How common are eyeglasses?

Eyeglasses are extremely common. Over 1 billion people around the world wear them.

What tests will I need before getting eyeglasses?

Before you get prescription glasses, you’ll need to undergo an eye exam. An eye care specialist, usually an optometrist or ophthalmologist, will do the exam and associated tests to check your sight. They’ll check if you have 20/20 vision (in places that use the metric system, it’s 6/6 vision).

Having 20/20 vision means your visual acuity is normal. If you don’t have 20/20 vision, your eye care specialist will determine how far off from 20/20 you are and what it’ll take to get you up to that. And if you already wear glasses, they’ll make sure your glasses are helping you adequately.

Not having 20/20 vision can go one of two ways:

• If the second number is less than the first: This is better-than-normal vision. For example, 20/15 vision means you can stand 20 feet away from something and see it clearly. Meanwhile, most people would have to get closer and stand 15 feet away to see it just as clearly as you.
• If the second number is greater than the first: This is worse-than-normal vision. For example, 20/30 vision means most people could stand 30 feet away from something and see it clearly. But you would need to stand closer, 20 feet away, to see it just as clearly as they do.

What are the different types of prescription eyeglasses?

There are many different varieties of eyeglasses. Some of the terms you might encounter include:

• Single-vision lenses. These are lenses with a single prescription change.
• Multifocal lenses. These are lenses with multiple prescriptions combined into a single lens. For example, a multifocal lens can have a prescription for close-up reading and another for seeing farther away.
• Bifocals. These are a type of multifocal lenses. “Bi-“ means they contain two different prescriptions. They usually contain a visible seam/edge that separates the prescriptions (they often look like a lens within a lens).
• Trifocals. These are also a type of multifocal lens. “Tri-“ means they contain three different prescriptions. These also usually have a seam between the different prescriptions, appearing like multiple lenses combined into a single piece.
• Progressive lenses. These are somewhat like bifocals, but there’s no seam. The prescription gradually changes from top to bottom. The lower part of the lens helps with close-up vision.
• Reading glasses. These are single-vision lenses that help with near vision. Their main use is helping people with presbyopia see up close for tasks like reading. Many people know them as “readers” or “cheaters” (a slang term from the 1920s that’s still in widespread use). You can often purchase these over the counter (OTC) at pharmacies, grocery stores and bookstores.
• Prism lenses. These lenses shift the light’s position before it enters your eye. That position shift helps with double vision due to eye misalignment.

Some types of lenses or glasses have very specific uses. You can often get these without a vision prescription in the lens, or as a prescription lens with the various features/capabilities built in. They include:

• Sunglasses. Sunglasses can have prescriptions built into the lens. This can be helpful if you need to wear glasses all the time and want to make it easier to block sunlight and see clearly at the same time.
• Computer glasses. Sometimes known as “blue-blockers” (or under the trademark “BluBlocker®”), these glasses block certain wavelengths of light. If you spend a lot of time looking at a computer screen, they can help ease eye strain and fatigue. You can also commonly get a blue-blocking coating on prescription lenses of any kind for this same reason.
• Photochromic lenses. These are also known as “light-adaptive” lenses or under the trademarked name “Transitions®.” They automatically darken when ultraviolet light hits them. The material can be part of the lens itself or in a coating applied to the lens’ surface.

What are the different types of lenses and lens materials?

When it comes to prescription lenses, you often have two choices: glass or plastic. Your eye care specialist or another eye care professional, like an optician, can tell you more about the options available. They can also explain the pros and cons, and tell you what different types of glass might do for you.

There are also a few different varieties of plastic available for use in prescription lenses. They all scratch easier than glass, but anti-scratch coatings help offset that disadvantage.

Common plastic materials include:

• Standard plastic. The most common plastic for prescription lenses is Columbia Resin #39 (known simply as “CR-39®” for short). CR-39 weighs half as much as glass, which helped it become a popular lens material.
• Polycarbonate. This type of plastic is light and yet very durable, and it’s more shatter-resistant than CR-39. The lenses can be even thinner and lighter than with CR-39, too. This material is especially popular for very active people, including kids. They’re also good for people with strenuous jobs where you’re more likely to damage your glasses.
• Trivex®. This is the lightest of the plastic materials available for prescription lenses. It’s also impact-resistant.
• High-index plastics. Similar to varieties of high-index glass, high-index plastics are useful for stronger prescriptions. But like their glass counterparts, high-index plastics also have durability issues and are prone to breaking.