Screens didn’t just get smaller—they got closer. That shift (from TVs across the room to phones inches from our eyes) changes the focusing work your visual system has to do and helps explain why “the same number of hours” on different devices don’t feel the same to your eyes. Below is a practical guide to why distance matters, how accommodation works, and how device classes (TV → PC → tablet → phone → VR) differ.
And here’s the catch: the closer the screen, the harder your eyes have to work. Humans weren’t built to spend 10+ hours a day with their lenses locked at just a few centimetres of focus—yet that’s exactly what modern work and leisure demand. No wonder we’re seeing a surge in complaints of digital eye strain, now refered as an emerging rising epidemic. read more about (Computer Eye Strain, 2025).
TL;DR
Screens didn’t just get smaller — they got closer. The nearer the screen, the harder your eyes must work. Phones at ~30 cm demand about 8–10× more focusing effort than a TV across the room. PCs and tablets fall in between, while VR creates a unique vergence–accommodation conflict — more about brain–eye mismatch than raw muscle effort.
Key takeaway: it’s not just screen time that strains your eyes, it’s how close those screens are.
How Accommodation Works (the 10-second version)
When you look at something close, your eyes have to refocus. They do this by tightening a tiny ring-shaped muscle inside the eye called the ciliary muscle, which squeezes the eye’s natural lens (the crystalline lens) and makes it rounder. A rounder lens bends light more strongly, so near objects come into focus. This process is called accommodation.
The closer the object, the more the muscle has to contract — just like flexing your arm harder to lift a heavy weight.
When you look far away, the opposite happens: the muscle relaxes, the lens flattens, and your eyes are basically at rest. That’s why staring out a window or across a room can feel so good after hours on a laptop or phone.
Accommodation usually works together with two other automatic responses:
- Convergence – your eyes turn inward to line up on the near object.
- Pupil constriction – your pupils get smaller to sharpen the image.
These three changes — focusing, turning in, and pupil tightening — happen almost instantly and in sync. Eye doctors often call them the near reflex or near focus triad.
Rule of Thumb: How Distance Translates Into Eye Work
Eye doctors measure focusing effort as accommodative demand, and the unit they use is diopters (D). A higher diopter number means your ciliary muscle is contracting more and working harder to bring something into focus.
The formula is simple: accommodative demand (in diopters) ≈ 1 viewing distance (m) .
This optics relation is a standard teaching in vision science (HyperPhysics, 2023).
Why it matters: focusing up close is like holding a dumbbell without putting it down — your eye muscles eventually tire. Add in reduced blinking, and it’s no surprise that screens leave eyes feeling dry and uncomfortable (Sheppard & Wolffsohn, 2018).
The Evolution: TV → PC → Tablet/Phone → VR
Over the past few decades, screens haven’t just changed in size and purpose — they’ve steadily moved closer to our faces. Each new generation of devices has pulled our eyes into a shorter viewing distance. This shift matters because closer screens demand more focusing effort and create different kinds of visual strain. Here’s how that evolution looks:
- Television: Large image at long distance. Low accommodative demand (~0.33–0.5 D), minimal vergence stress (SMPTE, 2016).
- PCs: Typical distance 50–70 cm. Demand ~1.4–2 D, sustained. AOA advises 20–28 inches (51–71 cm) for comfort (AOA, 2015).
- Tablets: Usually 30–50 cm, creating ~2–3.3 D demand. Apple warns children if held <30 cm (Apple, 2023).
- Smartphones: Mean ~33–37 cm, often closer in kids, increasing strain (Long et al., 2017).
- VR/AR Headsets: Project images at 1.3–2 m, but vergence varies with depth → vergence–accommodation conflict (Kramida, 2016).
Key takeaway: Looking at your phone just 30 cm away makes your eyes work 8–10× harder than watching TV across the room. In other words, just 1 hour on your phone can strain your eyes like 8–10 hours of TV time (Blehm et al., 2005).
Surprising Reality Check: VR vs. TV
You might think VR headsets are the “closest screens” and therefore the hardest on your eyes. In reality, they’re optically designed so the image appears at a distance — usually around 1.3–2.0 meters, similar to watching a TV across the room.
But here’s the catch: unlike TV, VR makes your eyes converge (turn inward) to follow objects that seem nearer or farther in the virtual world, while your actual focus (accommodation) stays locked at that fixed 1–2 m point. This mismatch — called the vergence–accommodation conflict — is unique to VR and is what often causes eye fatigue and discomfort, even though the focusing distance itself isn’t extreme (Kramida, 2016).
The strain is less about raw muscle effort and more about a brain–eye coordination problem. Read more in our detailed article: VR Eye Strain: Causes, Symptoms, and Fixes .
Why Distance Hits Hard: Three Mechanisms
- Higher focusing load: Prolonged near demand can cause headaches, blur, and difficulty refocusing (Ciuffreda, 2006).
- Vergence stress: Extra convergence increases symptoms when posture or refractive error are off (AOA, 2015).
- Blink suppression: Blink rates can halve during screen tasks, worsening dryness (Tsubota & Nakamori, 1993).
This mismatch between demand and focusing ability is a well-documented cause of symptoms like blur and headaches (Ciuffreda, 2006).
Children & Viewing Distance: Why It Matters
Kids don’t just use screens differently — they literally hold them closer. Research shows children often bring devices in at just 18–25 cm, compared to adults’ typical 30–40 cm or more (CooperVision, 2023; Myopia Profile, 2023; My Kids Vision, 2023; Apple, 2023). Holding things that close increases the accommodative demand, putting more continuous strain on their developing eyes.
Here’s what that means for their eyes:
- TV at 3.0 m → ~0.33 D (almost no effort).
- Adult phone use at 33 cm → ~3.0 D (about 9× more effort).
- Kids’ phone use at 20 cm → ~5.0 D (15× the TV effort, nearly double adult phone use).
Put simply: 1 hour of phone use at a child’s distance can strain the eyes like 15 hours of TV. And it’s not just short-term fatigue — research links prolonged close-up work at these distances with faster childhood myopia progression, especially when kids also spend less time outdoors (Rose et al., 2008; Myopia Profile, 2023; My Kids Vision, 2023).
Read more in our in-depth guide: Kids & Screen: What Parents Need to Know .
Final Thoughts
Your eyes aren’t just tired from “too much screen time” — they’re tired from how close those screens are. A phone session at arm’s length can be eight times more demanding than watching TV across the room, and VR introduces its own unique brain–eye conflict.
Over time, this constant near-work is why digital eye strain has become such a common complaint in today’s always-online world. The fix isn’t just fewer screens, but smarter screens: pushing devices further away, making text bigger, taking regular breaks, and remembering that your eyes are happiest when they get to relax and focus on the distance.
Frequently Asked Questions
Why does viewing distance matter for eye strain?
The closer a screen is, the more your eye muscles must contract to keep it in focus. Prolonged near-focus increases strain and can reduce blinking, leading to digital eye strain and dryness.
Is looking at a phone worse than watching TV for my eyes?
Yes. Focusing on a phone at around 30 cm demands about 8–10 times more effort than watching TV from 3 meters away, which is why phone use feels more tiring over time.
Does VR cause the same kind of strain as phones and computers?
Not exactly. VR images are projected at a distance of 1–2 meters, similar to TV, but the brain receives conflicting depth signals. This vergence–accommodation conflict can cause fatigue and discomfort even without extreme close-up focusing.
How can I reduce eye strain from close screens?
Increase your viewing distance when possible, enlarge text, take regular breaks using the 20-20-20 rule, and look into the distance to let your eyes relax.
References
- American Optometric Association (2015) Computer Vision Syndrome. St. Louis: AOA.
- Apple (2023) About Screen Distance on iPad and iPhone. Cupertino: Apple Inc.
- Blehm, C., Vishnu, S., Khattak, A., Mitra, S. & Yee, R. W. (2005) ‘Computer Vision Syndrome: A Review’, Survey of Ophthalmology, 50(3), pp. 253–262.
- Ciuffreda, K. J. (2006) ‘Accommodation, the Pupil, and Presbyopia’, in Benjamin, W. J. (ed.) Borish’s Clinical Refraction. 2nd edn. Philadelphia: Saunders, pp. 93–144.
- HyperPhysics (2023) Optics of the Eye. Georgia State University. Available at: http://hyperphysics.phy-astr.gsu.edu/hbase/vision/accom.html
- Kramida, G. (2016) ‘Resolving the Vergence–Accommodation Conflict in Head-Mounted Displays’, IEEE Transactions on Visualization and Computer Graphics, 22(7), pp. 1912–1931.
- Long, J., Cheung, R., Duong, S., Paynter, R. & Asper, L. (2017) ‘Viewing Distance and Eyestrain Symptoms with Extended Use of Mobile Phones’, Clinical and Experimental Optometry, 100(2), pp. 133–137.
- SMPTE (2016) Recommended Practice RP166: Television Viewing Distance. White Plains: Society of Motion Picture and Television Engineers.
- Sheppard, A. L. & Wolffsohn, J. S. (2018) ‘Digital Eye Strain: Prevalence, Measurement and Amelioration’, BMJ Open Ophthalmology, 3(1), e000146.
- Tsubota, K. & Nakamori, K. (1993) ‘Dry Eyes and Video Display Terminals’, New England Journal of Medicine, 328(8), pp. 584.
- CooperVision (2023) Children and Screen Time: Why Viewing Distance Matters. Available at: https://coopervision.com (Accessed: 4 September 2025).
- Myopia Profile (2023) How are Screens Different from Books in Myopia? Available at: https://www.myopiaprofile.com/articles/how-are-screens-different-from-books-in-myopia (Accessed: 4 September 2025).
- My Kids Vision (2023) Children’s Screen Time and Myopia Risk. Available at: https://www.mykidsvision.org (Accessed: 4 September 2025).
- Rose, K.A., Morgan, I.G., Ip, J., Kifley, A., Huynh, S., Smith, W., and Mitchell, P. (2008) ‘Outdoor activity reduces the prevalence of myopia in children’. Ophthalmology, 115(8), pp. 1279–1285. doi:10.1016/j.ophtha.2007.12.019.