If you are experiencing difficulty reading smaller print or holding reading material farther away from your face than is comfortable, it may be time to purchase new readers.

Figuring out the right pair can be daunting, but this guide will help make it easier for you to determine which reading glasses strength is best.

What Is a Diopter?

A diopter (pronounced “dah-opt”) is the unit of measurement for an eyeglass or contact lens prescription. It describes the focusing strength of the lenses. With a simple refraction test, your eye care professional determines your focusing strength or prescription.

Refraction involves holding a set of lenses with different strengths in front of your eyes and asking you to try to focus on an object or chart. It enables your eye care professional to calculate the exact focusing error you are experiencing. The numbers describing your focusing strength appear on the bottom of your glasses or contact lens prescription.

A defining feature of a lens is its optical power, which is the ability to cause an incident pencil of parallel light rays to converge or diverge. A lens with a lens power of three diopters will bring light rays to focus at 1/3 of a meter away from the lens. On the other hand, a flat window will not have a lens power of 3 diopters because it causes light rays to focus at an infinite distance.

In photography and cinematography, a lens’s optical power is often expressed in terms of its focal length in millimeters. It makes sense because a lens’s focusing ability is proportional to its focal length. However, it is essential to note that optical power and focal length are not interchangeable units of measurement.

Diopter Test Charts

A diopter test chart is a great way to gauge which reading glasses strength will be best for you. These charts typically feature rows of text that get smaller and smaller with a corresponding diopter number next to each row. Typically, the first line you can read indicates your reading glass strength, though it may take some trial and error to find this line.

You can often find these charts online or at many optical retailers that carry reading glasses, and they are a quick and easy way to determine your eyeglass’s strength. To use the chart, remove your glasses or contact lenses and hold them up to your face approximately 14 inches away from your eyes.

Then, read the lines from the top (most minor text) and work down the page. Reaching the first line that is difficult to read will indicate the strength of your reading glasses.

Selecting the correct pair of reading glasses will help your eyes by preventing unnecessary strain and fatigue. The proper reading glasses strength will allow you to enjoy your favorite books, magazines, or newspapers without focusing on the small print or holding your materials uncomfortably close to your face.

You will also prevent eye strain and headaches from using a pair of reading glasses that are too powerful or do not match your needs.

Diopter Charts for Contact Lens Wearers

Whether purchasing reading glasses over the counter or at an eye doctor, a diopter chart will help you find the perfect pair for your needs. These sheets of text have rows ranging in size that correspond to certain magnification levels – the lower the number, the less intense the lens.

Typically, you will hold the sheet 14 inches away from your face and read down the rows until you can identify a line that looks crystal clear. If you have mismatched strengths in your eyes, cover one eye and repeat the test with the other until you hit a reading glasses strength that works for both eyes together.

Once you’ve identified a power that suits your eyes, testing several pairs of glasses with the same strength is often helpful. If you’re buying over-the-counter readers at a retail store, you can also test out weaker and stronger pairs than the initial results you received from the diopter chart test.

In most cases, choosing reading glasses that are a little weaker is preferable to ones that are too strong. However, some people require reading glasses with a higher magnification level to focus on closer items like maps or restaurant menus. If this is the case, visit a trusted optometrist for professional advice.

The Foster Grant Diopter Chart

While it’s tempting to buy a pair of reading glasses from a local store or online, this type of solution often provides a temporary fix and may not be an accurate fit for your eyes. Instead, if you purchase your reading glasses, you should visit an optometrist for a complete eye exam.

It will enable you to try different frames and a more comprehensive range of strength options. However, if you cannot make an appointment with your optometrist, you can still test out several pairs of over-the-counter readers and narrow down your search for the correct power.

The easiest way to figure out what your lens power should be is by using a diopter chart. You can find one online or purchase a printable version from your optometrist. The chart will have rows of words ranging in text size that different strength lenses can read.

Start by holding the chart 14 inches away from your face and attempting to read the most minor line of words. Continue reading down the chart until you find a line that you can see. The number to the right of the first line you read will indicate the lens strength (or magnification) you need for your reading glasses.

Reading glasses can be an affordable and efficient remedy for people who suffer from presbyopia. Finding the correct strength of your reading glasses can make a difference in how well you can read and focus on close-range objects.