Screen Eye Strain Calculator
Calculate digital eye strain risk from daily screen hours, viewing distance, break frequency, and lighting.
Returns a risk score with tips to reduce symptoms.
Computer Vision Syndrome (also called Digital Eye Strain) affects an estimated 50–90% of people who work at computer screens. Symptoms include eye fatigue, dryness, blurred vision, headaches, and neck pain.
Key risk factors:
Screen distance: The ideal distance is 20–26 inches (50–65 cm) from your eyes. Screens closer than 16 inches (40 cm) force your eye muscles to work significantly harder to maintain focus. Every inch closer increases strain exponentially.
Screen time duration: Risk increases dramatically after 2 continuous hours. The average office worker spends 6–8 hours looking at screens daily. Adding phone and TV use, many people exceed 10 hours total.
The 20-20-20 Rule: Every 20 minutes, look at something 20 feet (6 meters) away for at least 20 seconds. This relaxes the ciliary muscles that control focus. Studies show this simple practice reduces eye strain symptoms by 30–40%.
Blink rate: Normal blink rate is 15–20 times per minute. When staring at screens, blink rate drops to 5–7 times per minute, causing dry eyes. Consciously blinking more often helps, as does using artificial tears.
Lighting: Glare from overhead lights or windows reflecting off your screen is a major contributor. Your screen brightness should match the ambient light level - not brighter, not dimmer. A too-bright screen in a dark room is particularly harmful.
Blue light: Blue light (400–490 nm wavelength) from screens can disrupt sleep patterns when viewed in the evening. While blue light blocking glasses are popular, research on whether they reduce eye strain during daytime use is inconclusive. The bigger factor is overall screen habits.
Tip: Position your screen so the top of the display is at or slightly below eye level. Looking slightly downward reduces the exposed surface area of your eye, which slows tear evaporation.
How the score is built
Four factors, 100 points between them. The weights follow how much each one actually shifts symptom rates in the workplace studies, which is why raw hours carries the most and lighting the least.
| Factor | Points at worst | Points at best |
|---|---|---|
| Daily screen hours | 40 (at 10 hours or more) | 0 (no screen time) |
| Screen distance | 25 (under 16 in / 40 cm) | 3 (over 26 in / 65 cm) |
| Break frequency | 20 (rarely or never) | 0 (every 20 minutes) |
| Lighting | 15 (glare or bright overhead) | 2 (matched to the room) |
Screen hours score at 4 points per hour and stop climbing at 40, because past ten hours a day the other three factors decide whether you get symptoms, not the total.
Under 20 is low risk, 20 to 39 mild, 40 to 59 moderate, 60 to 79 high, and 80 or more very high. The bands are a rough guide to how likely daily symptoms are, not a diagnosis. Distance and breaks are the two you can usually change today; hours are usually set by your job.
One point the score cannot capture: an uncorrected prescription. If you already sit at a sensible distance, take breaks, and still get headaches by mid-afternoon, an eye exam is worth more than any setup change. Presbyopia starting in the early forties shows up at a computer first, because the working distance is exactly where the loss of accommodation bites.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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