Short answer: Screens are harder on your eyes than physical books for most people — primarily because of reduced blink rate, self-luminance, and the tendency to use screens for far longer sessions. But both cause fatigue if used for hours without breaks.
Head to head
The blink rate difference
The biggest practical difference between screens and books is blink rate. Studies consistently show that screens suppress blinking more than books — roughly 60–70% reduction versus 30–40% for print reading. The self-luminous nature of screens appears to be a significant factor: the brain allocates more attention to processing a light-emitting source, further suppressing the blink reflex.
This matters because blink rate is the primary determinant of tear film health and therefore of dryness, burning, and eye fatigue. The extra 30–40% reduction on screens translates directly to more dryness and faster symptom onset.
Where books are also hard on eyes
Physical reading is not without strain. Sustained near focus causes the same accommodative fatigue as screen use — the ciliary muscle works just as hard to focus on a book at 30cm as a screen at the same distance. Poor reading posture, reading in low light, and small print all amplify this. The 20-20-20 rule applies equally to book reading.
E-readers are somewhere between the two — they use reflected light like physical books, which is gentler, but shares the blink-suppression effects of screens. Front-lit e-readers with warm light settings perform better than backlit tablets for eye comfort.
The session length factor
One underappreciated reason screens cause more eye strain than books in practice: sessions are much longer. Most people naturally put a physical book down after an hour or two. Screens — particularly when used for work — run for 6–8 unbroken hours. Total exposure time is a major variable, independent of the per-hour strain rate.