Eye Strain Signals: Blink Rate, Eyes-Closed Seconds, And Microsleeps
Blink rate alone is noisy. Eyes-closed seconds and microsleep events are stronger signals, especially when read together against your own baseline.
Why eye signals show up before fatigue feels obvious
Most fatigue tracking apps rely on what you tell them. Sarenica leans heavily on what your camera sees, because the eyes start drifting before most people notice they are tired.
Three signals do most of the work in this layer: blink rate, eyes-closed seconds per minute, and microsleep events. Each one is noisy on its own. Read together, against your own baseline, they get useful fast.
Blink rate, and why it is the easiest signal to misread
A normal screen-facing blink rate sits around 12 to 18 per minute. Drop into deep focus and it can fall to single digits. That is not necessarily strain; it can be concentration.
That is exactly why blink rate alone is a weak fatigue signal. It moves with focus, with screen task type, with light, and even with how you sit. Sarenica records it because it is one input into a larger read, not because it is conclusive on its own.
Eyes-closed seconds, the more honest signal
Eyes-closed seconds counts how many seconds in a minute your eyes were closed beyond a normal blink. It captures heavy blinks, long blinks, and the small unconscious pauses that creep in when you are pushing through.
It is more honest than blink rate because it does not move much with normal focus. A long-blink pattern is a quieter, more reliable strain tell.
In your own data, you will usually see this number stay near zero through morning blocks, then climb in the afternoon, then climb again in late evening. The shape matters more than the absolute number.
Microsleep events, and why they matter even when rare
A microsleep event is a brief involuntary closure long enough that the system flags it as more than a blink. They are rare in normal work; you might see zero for days at a time.
When they show up, they almost always cluster around a specific hour or after a specific session length. That is the whole reason the signal exists: not to count strain in real time, but to retroactively explain a block that looked off.
If a weekly report says your worst block was Wednesday at 14:00 and the microsleep events line shows a small spike there, you have a much stronger explanation than guessing.
How Sarenica combines them
No single eye signal triggers a fatigue call. Sarenica reads them as a small panel: blink rate as context, eyes-closed seconds as the burden line, microsleep events as the rare exception evidence.
They feed into a per-minute eye-strain score, which then feeds into the larger fatigue and focus reads. That is why your weekly report can say "30-45 minute sessions show 38% higher fatigue" without ever saying "your eyes were tired" — the eye signal is folded in upstream.
What to do once a pattern repeats
Single days do not matter much. A repeating pattern across normal workdays does. If eyes-closed seconds reliably climbs after 11:00, the question is no longer "am I straining" but "what changes if I cap demanding blocks at 30 minutes before noon".
That is the kind of question your weekly report is built to answer. The eye signals are the why; the report is the so-what.