Most eye glitches are harmless. A few are not, and the difference is usually clear within a minute if you know what to check. Start with the red box. If none of it applies, the two checks after it will tell you which kind of glitch you have.
A shadow or curtain moving across part of your vision; a sudden shower of new floaters, or new flashes of light at the edge of your vision; sudden loss of vision in one eye, even if it comes back; visual disturbance together with weakness or numbness on one side, difficulty speaking, or facial droop; a first-ever aura after age 50; or an aura that lasts longer than an hour. None of these are screen fatigue.
Check 1: cover one eye
While the glitch is happening, cover your left eye, then your right.
- You still see it with either eye covered. The glitch is in the visual part of the brain, not in one eye. The usual cause is a migraine aura.
- You only see it with one eye open. The glitch is in that eye: the tear film, the gel inside the eye, or the retina.
- You feel it more than you see it. It is probably the eyelid muscle, not your vision.
Check 2: time it
- Gone after a blink. Tear film.
- Grows over several minutes, then fades within an hour. Migraine aura.
- Comes and goes in bursts over days. Eyelid twitch.
- Drifts when you move your eye, and has been there for months. Floaters.
- Only on one screen, worse at low brightness. The display.
The five glitches
| What you notice | Most likely cause |
|---|---|
| Lid flutters; image may jump slightlyBursts over days; you can feel it | Eyelid myokymia — benign |
| Smeary, shimmering patchOne eye; clears with a blink | Tear film breaking up |
| Flicker on the screen itselfLow brightness; one display only | Display dimming (PWM) |
| Shimmering zigzag that spreadsBoth eyes; 5–60 minutes | Migraine aura — see a doctor if new |
| New floaters or flashesOne eye; sudden onset | Urgent eye exam |
1. The eyelid twitch
A fine, rhythmic flutter of the lower or upper lid, usually on one side. It is called eyelid myokymia. You feel it much more than anyone else can see it. If the lid moves into your line of sight, the image may seem to jump slightly. It comes in bursts for days or weeks and then stops on its own. The common triggers are poor sleep, stress, caffeine, and dry, irritated eyes. Everything about it, including when it is not benign, is in eye twitching at a screen.
2. Tear-film blur
A smeary or shimmering patch, often in the centre of your vision, that appears after several seconds of staring and clears the moment you blink. During focused screen work, blink rate falls by roughly two thirds. The tear film on the front of the eye breaks up between blinks, and the broken film bends light unevenly. This is the most common "glitch" for people at a screen, and the least serious. The five-second blink test in blurry vision after screen work confirms it.
3. Display flicker
Some displays dim by switching the backlight on and off very fast, a method called pulse-width modulation (PWM). Most people do not notice it. Some people are sensitive to it and get a shimmering effect, discomfort or headaches, mainly at low brightness. Clues: the effect appears on one screen and not on another, and it gets worse as you turn the brightness down. Pointing a phone camera at the screen sometimes shows dark bands rolling across it, which suggests PWM. If this is you, keep the screen brightness higher and add room light instead of dimming the screen, or choose a display that dims without PWM.
4. Migraine aura
A small bright or shimmering spot, often with a zigzag edge, that slowly grows into a C-shape and drifts toward the edge of your vision over several minutes. Each aura symptom typically lasts between 5 and 60 minutes. A headache often follows within an hour, but not always: aura without headache is common, especially with age. Because the aura comes from the visual cortex, you see it with either eye covered.
A first aura deserves a medical check, to confirm that it is migraine and to rule out the conditions in the red box. Once diagnosed, a typical aura is not dangerous. Screen work does not cause migraine, but bright light, glare, long sessions without breaks and poor sleep are common triggers for people who already have it.
Headache Classification Committee of the International Headache Society (2018). The International Classification of Headache Disorders, 3rd edition. Cephalalgia, 38(1), 1–211.
5. Floaters and flashes
Dots, threads or cobwebs that drift when you move your eye, most visible against a bright screen or a white wall. Long-standing floaters are common and harmless. A sudden change is different. New floaters, new flashes of light, or a shadow at the edge of your vision can mean the gel inside the eye is pulling on the retina. That needs an eye exam the same day, because a retinal tear treated early is a much smaller problem than a retinal detachment.
When it is constant
A glitch that never stops — fine static across the whole field of vision, day and night, for months — is a different category. One cause is a condition called visual snow. It is rare, it is not caused by screens, and it needs a neurologist or neuro-ophthalmologist rather than an optometrist.
The short version
- Clears with a blink: tear film. Blink fully and more often.
- Felt in the lid, comes and goes for days: myokymia. Sleep, less caffeine, wait.
- Spreads over minutes, visible with either eye: migraine aura. Get a first one checked.
- One screen, low brightness: the display. Raise the brightness.
- New floaters, flashes or a shadow: same-day eye exam.
The glitch that clears when you blink.
If your vision smears during screen work and sharpens after a blink, the tear film is drying between blinks. Skopia is a quiet Mac menu bar app that prompts a full blink on a timer. No camera, no subscription, no account.
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