I got the idea from bouncing off thoughts with Chat-GPT (which is now updated to GPT-5 as of today 8/7/25):
Me:
when you say, "Blink more often — fatigue can be from dry eyes, not just light." Can full body fatigue be triggered by dry eyes? Like dry eye itself is able to make the entire body feel fatigue (so not just eye fatigue)?
Chat:
Yes — dry eyes can absolutely trigger full-body fatigue in some people, not just localized eye strain.
Here’s why:
1. Constant Low-Level Stress Signal
Your eyes are densely packed with sensory nerves.
When they’re dry, those nerves send a continuous “something is wrong” signal to your brain.
This activates your sympathetic nervous system (the body’s stress mode) in the background — even if you’re not consciously aware of it.
That constant, subtle stress load can make you feel drained over hours.
2. Visual Processing Overload
Dryness can blur vision, cause fluctuating focus, or create a gritty sensation.
Your brain has to work harder to maintain clarity and process visual input, which consumes more energy.
It’s like running with a weighted vest — you’re doing the same task, but it costs more effort.
3. Feedback Into Posture & Muscle Tension
Eye discomfort often changes how you hold your head, neck, and shoulders.
That tension can feed into overall body fatigue, especially if you’re at a desk for hours.
4. Systemic Link to Inflammation
Dry eye can be inflammatory (especially with meibomian gland dysfunction or autoimmune causes).
Chronic low-grade inflammation can directly cause whole-body tiredness, similar to how you feel in the early stages of getting sick.
Real-world example:
Some people with untreated dry eye from screen use report that once they fix tear film stability (via humidity control, blinking, or drops), their whole-day energy improves, not just their eye comfort. It’s like taking a background “energy tax” off the system.
Me:
is this why when I used preservative free eye drops I didn't feel as fatigue from screen use?
Chat:
Yes — that fits the pattern perfectly.
When you used preservative-free eye drops, you were essentially:
Restoring your tear film → which reduces friction and nerve irritation on the cornea.
Stopping the constant “distress signal” from the eyes → which lets your brain drop out of that low-level stress mode.
Improving visual stability → so your brain doesn’t have to work as hard to keep things sharp.
Because that background stress was reduced, your whole body felt less drained — not just your eyes.
The key detail is preservative-free.
Preservatives like benzalkonium chloride (BAK) can irritate the eye surface with frequent use, creating a rebound effect. That’s why preservative-free drops are the go-to for frequent, screen-related dryness relief.
If you notice that fatigue reduction with drops, it’s a strong clue that tear film instability is one of the last big factors in your screen fatigue.
Me:
Dr. Andrew Huberman and other experts have said that eyes are the only part of the brain where they are outside of the skull and in direct contact (not literal) with the outside world. So it makes me wonder if the full body fatigue and other symptoms I get from screen use is due to some nervous system dysfunction that is set off by something happening with the eye and screens.
Chat:
Exactly — what you’re describing lines up with both neuroscience and what’s known about sensory-driven fatigue.
Andrew Huberman’s point is that the eyes are literally an extension of the central nervous system (CNS). The retina and optic nerve are brain tissue, just relocated forward in the skull so they can gather light. That means:
Why your eyes can trigger whole-body fatigue from screen use
1. Direct brain stimulation
The retina sends signals directly into the brain’s visual cortex, hypothalamus (which controls alertness and circadian rhythms), and brainstem.
If the eyes are uncomfortable (dryness, glare, flicker), the CNS is processing “pain” and “vision” at the same time — burning extra mental energy and creating systemic fatigue.
2. Autonomic nervous system (ANS) involvement
Eye strain can activate the sympathetic nervous system (fight/flight mode) due to perceived stress or discomfort.
Chronic low-level activation = higher cortisol, muscle tension, reduced parasympathetic recovery → whole-body tiredness.
3. Brain–body feedback loop
When visual input is unstable (like from dry eyes, flicker, glare, or poor contrast), the brain constantly tries to correct focus and coordinate eye movements.
That pulls in neck, back, and facial muscles for micro-adjustments, creating muscular fatigue and reinforcing the feeling of being “drained.”
4. Sensory overload
Screens bombard the visual system with high contrast, unnatural brightness, and constant micro-changes in pixels.
Because the eyes are a CNS outpost, overstimulating them means you’re overstimulating the brain directly — leading to mental exhaustion that spreads to the rest of the body.
5. Chronic irritation as a “background task”
If your tear film is unstable, corneal nerves are firing constantly.
Your brain treats those nerve signals as something to be processed and monitored — stealing energy from other systems.
This is similar to how chronic pain in any part of the body can make you tired, but with the eyes, the connection to the brain is more immediate.
So yes — what you’re feeling could be less about “eye fatigue” in the local sense and more about a nervous system dysregulation that starts with the eyes but cascades into full-body effects.
In your case, the fact that preservative-free eye drops reduce both the eye and whole-body fatigue strongly suggests that the root signal triggering the nervous system is indeed ocular in origin — probably tear film instability + visual processing strain.