About

Digital Eye Strain (DES), also known as Computer Vision Syndrome, affects nearly 60% of people who use computers daily. The 20-20-20 Rule, popularized by optometrist Dr. Jeffrey Anshel, is the gold standard for mitigation. The logic is simple but effective: Every 20 minutes, look at something 20 feet (6 meters) away for 20 seconds.

This tool automates that discipline. Unlike standard timers, it uses a dedicated background worker to ensure precision even when you are focused on other tabs. It features a synthesized 432Hz calming chime to gently alert you without inducing stress, allowing your ciliary eye muscles to relax and reset their focal distance.

Formulas

The 20-20-20 Rule can be formalized as a cycle of strain accumulation and release:

T_cycle = t_work + t_rest

Where:

t_work = 20 min

t_rest ≥ 20 s

Optimal Focal Distance during t_rest:

d_focus ≈ ∞ (Optical Infinity, approx. 6m)

Reference Data

Parameter	Standard (Imperial)	Standard (Metric)	Physiological Benefit
Work Interval	20 minutes	20 minutes	Prevents tear film evaporation and blink rate reduction.
Break Duration	20 seconds	20 seconds	Minimum time required for eyes to fully relax focus.
Focal Distance	20 feet	6 meters	Relaxes the ciliary muscles (infinity focus).
Blink Rate	15-20 / min	15-20 / min	Rehydrates the cornea.
Screen Distance	20-28 inches	50-70 cm	Reduces convergence fatigue.

Frequently Asked Questions

It takes approximately 20 seconds for your eyes to fully relax their focus muscles (ciliary muscles) after locking onto a close-range screen for an extended period. Shorter breaks do not allow for a complete reset.

Not necessarily, but it helps. The primary requirement is optical: look away from the screen at a distant object. However, combining this with standing up aids blood circulation, addressing sedentary fatigue simultaneously.

Yes. This tool uses a Web Worker thread, meaning the timer continues to count down accurately even if you minimize the browser or switch to a heavy application.

The timer generates a soft sine wave at approximately 432Hz (Verdi's A), often associated with relaxation, to avoid the "startle response" caused by harsh alarm clocks.