Computer glasses are typically 0.50 to 1.00 diopters weaker than your reading glasses. Standard reading glasses are designed for material held about 12 to 16 inches from your face, but a computer screen sits 20 to 28 inches away. That greater distance requires less magnification, so wearing your full reading prescription at a computer will often cause eyestrain, headaches, or blurred vision.
How to Calculate Your Computer Strength
The simplest approach is to start with your reading glasses power and subtract based on how far your screen sits from your eyes. If your monitor is on the closer end (20 to 24 inches), subtract about 0.50 diopters. If it’s farther away (24 to 28 inches or more), subtract 0.75 to 1.00 diopters.
So if you wear +2.00 readers for books, you’d likely need +1.00 to +1.50 for computer work. Someone with +1.50 readers would try +0.75 to +1.00 for a screen at arm’s length. The exact number depends on your personal setup and how your eyes focus, but this formula gives you a reliable starting point.
If you don’t already have a reading prescription, age offers a rough guide. Presbyopia, the gradual loss of close-up focusing ability, typically becomes noticeable in the early to mid-40s and progresses until around age 65. Ready-made reading glasses range from +1.00 to +3.00 diopters, and your reading needs increase along that spectrum as you age. Whatever reading strength works for you at a bookstore display rack, step it down by the amounts above for computer use.
Why Regular Readers Don’t Work at a Computer
Reading glasses focus your eyes at roughly 14 to 16 inches. When you wear them at a computer 24 inches away, the magnification is too strong for that distance. Your eyes strain to compensate, or you unconsciously lean forward to get the screen into the lens’s focal range. The American Optometric Association notes that people often tilt their heads at odd angles or hunch toward the screen when their glasses aren’t designed for computer distance, and those postures lead to muscle spasms and pain in the neck, shoulders, and back.
Common signs you’re using the wrong strength at your computer include eyestrain, headaches, blurred vision, dry eyes, and neck or shoulder pain. If you find yourself pulling your head back from the screen or pushing your chair closer, your lenses are probably too strong for the distance.
Single Vision vs. Occupational Lenses
You have a few options once you know your computer power. The simplest is a pair of single-vision glasses set to your intermediate (computer) distance. These work well if you spend most of your screen time at a fixed distance and don’t need to read printed documents at the same desk. The tradeoff: distance vision will be blurry through them, so you’d take them off to walk around or look across a room.
Occupational progressive lenses (sometimes called “office progressives” or “near-variable focus” lenses) cover two zones. The upper portion is optimized for screen distance, roughly 2 to 5 feet, while the lower portion provides extra power for close tasks like reading a printout or checking your phone. Some versions include a small zone at the very top for limited distance viewing, useful if you attend meetings or give presentations without switching glasses. These are not the same as standard progressive lenses, which prioritize distance vision and squeeze the computer zone into a narrow corridor.
If your work is almost entirely on a single monitor at a consistent distance, single-vision computer glasses are the clearest, widest-field option. If you frequently shift between a screen, printed pages, and looking across a room, occupational progressives handle those transitions without swapping pairs.
Setting Up Your Screen for the Right Distance
Your glasses can only do their job if your monitor is positioned correctly. OSHA recommends placing the screen 20 to 40 inches from your eyes, with the top of the monitor at or slightly below eye level. The center of the screen should sit about 15 to 20 degrees below your horizontal line of sight. This lets you look slightly downward, which is the natural resting angle for your eyes and reduces strain on both your eye muscles and your neck.
If you use a laptop, the screen is often too low and too close, which pulls you into a forward hunch. A laptop stand paired with an external keyboard can fix both problems. For dual monitors, angle them so you don’t have to turn your head more than about 35 degrees in either direction, and keep both screens at the same distance from your face so one pair of computer glasses works for both.
How to Test Before You Commit
Inexpensive over-the-counter readers make it easy to experiment. Buy two pairs in strengths that bracket your estimated computer power. If you calculated +1.25, grab a +1.00 and a +1.50. Sit at your normal workstation and spend 15 to 20 minutes with each pair. The correct strength will let you read text on screen comfortably without leaning in or squinting, and you shouldn’t feel any pulling sensation behind your eyes after several minutes of use.
This approach works well if both of your eyes have similar vision. If you have significant differences between your eyes, astigmatism, or an existing prescription for distance, over-the-counter readers won’t match what you need. In that case, a prescription set specifically to your intermediate distance will be far more comfortable and accurate.