Human eyes evolved to handle sunlight and firelight, not eight-plus hours of fixed-distance, backlit screens refreshing at rates the eye has to constantly track. Ophthalmologists refer to the resulting symptom cluster as digital eye strain, or computer vision syndrome.
Several factors compound when using screens for extended periods: reduced blink rate (people blink significantly less often when focused on a screen, leading to dryness), sustained near-focus that fatigues the ciliary muscle, and glare or poor screen contrast that forces the eyes to work harder to resolve detail.
The American Optometric Association recommends the 20-20-20 rule: every 20 minutes, look at something 20 feet away for at least 20 seconds. This is one of the best-evidenced, zero-cost interventions for digital eye strain. Adjusting screen brightness to match ambient lighting, increasing text size to reduce squinting, and consciously blinking more often during screen sessions also help in the short term.
For longer-term nutritional support, ingredients like lutein and zeaxanthin (which filter blue light in the macula) and bilberry extract (studied specifically for ciliary muscle fatigue) have research behind them — see our lutein/zeaxanthin guide and bilberry guide for details.