Why do my eyes get tired when I read?

Short answer: the usual causes are reduced blinking, small type, poor contrast, bad lighting, and uncorrected vision. People blink far less while concentrating on text, especially on screens, and each missed blink leaves the eye surface drier. Most reading strain responds to a few setup changes and regular breaks. Strain that persists after those changes is a reason to book an eye exam, because uncorrected vision is one of the most common causes.

Blinking drops when you concentrate

A normal blink rate is around 15 to 20 blinks per minute. During focused screen work it can fall to a third of that, and many of the blinks that remain are partial. Blinks spread the tear film that keeps the surface of your eye smooth and comfortable. Fewer and weaker blinks mean a drier surface, and a drier surface produces the burning, gritty, heavy-lidded feeling most people call tired eyes.

Awareness helps more than it sounds like it should. When your eyes start to feel dry, close them fully for a second or two, a few times. Screens sit lower in the dry-eye rankings when they sit lower physically: looking slightly downward at a page or screen exposes less eye surface to the air than looking straight ahead.

Take breaks: the 20-20-20 rule

The advice optometrists give most often for screen fatigue is the 20-20-20 rule: every 20 minutes, look at something at least 20 feet away for at least 20 seconds. The point is to relax the focusing muscles, which hold a constant contraction while you look at anything close. Reading is close work whether the page is paper or glass, so the rule applies to both. Chapter breaks and section breaks are natural moments for it. A 20-second window glance costs you nothing measurable in reading progress over an evening.

Make the type bigger

Small type forces your focusing system and your eye muscles to work harder for every line, and it invites leaning in, which makes everything worse. On a phone or e-reader, raise the font size one or two steps past the point where it first looks comfortable. Nobody audits your font size. Larger type means fewer letters per line and a bit more scrolling, and that trade is nearly always worth it. On paper, the equivalent fix is holding the book 14 to 16 inches away in strong light rather than close to your face in weak light.

Contrast and lighting

Dark text on a light background at full contrast is the easiest arrangement for most eyes. Low-contrast schemes, such as gray text on white, look stylish and read badly. At night, a light-on-dark theme with the brightness turned down is comfortable for many people, and preference varies, so try both.

Room lighting should roughly match the screen. A bright screen in a dark room and a dim screen next to a sunny window both force your eyes to adapt continuously. For paper, put the light source behind or beside you so it lands on the page without glaring into your eyes. Position screens to avoid reflections from windows and lamps, since fighting glare is constant low-level work for your visual system.

When to see an optometrist

If your eyes tire within minutes of starting, if reading gives you headaches, or if strain persists after you fix blinking, breaks, type size, and lighting, book an eye exam. Small uncorrected errors, astigmatism among them, can be invisible in daily life and still make sustained close focus exhausting. From the early 40s onward, presbyopia gradually reduces near focus in nearly everyone, and reading glasses fix it cheaply. An exam costs less than most people spend on coffee in a month and settles the question. Persistent strain has a boring, correctable cause often enough that skipping the exam is a bad bet.

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