Vision training tool
Compute optotype sizes from the international standard (h = 2 × d × tan(θ/2), θ = 5/V arcminutes) and generate a 20-20-20 rest plan plus near-far focus training for self-testing and eye relaxation.
Runs in your browserEvery computation happens in your browser — your data never leaves this device.
Result
Optotype sizes or a training plan.
Enter an acuity value to calculate
Acuity: 0 · Optotype mm: 0 · Optotype px: 0 · Rounds: 0
What this tool does
- Build your own chart: get the millimetre and pixel height of each acuity step at your chosen distance and lay out a rough chart on screen.
- Pair with rest reminders: use the 20-20-20 plan to schedule each distant-focus break instead of staring at a nearby screen.
- Near-far training: follow the 33 cm near point and 6 m far point routine to ease the blurred feeling after long screen sessions.
- Check your screen: compare the computed pixel sizes with the real display to see whether browser or system scaling is distorting the optotypes.
Example
Input
1.0
Output
视力（小数记录法）：1 检查距离：600 cm（6 m） 视标张角：5 角分（1.0 视力为 5 角分） 该行视标高度：8.73 mm = 33 px（按 96 dpi 换算） 换算依据：h = 2 × d × tan(θ/2)，θ = 5/V 角分；px = mm ÷ 25.4 × 96 对照表（距离 600 cm 时各行视标高度）： 0.10：87.27 mm（329.8 px） 0.12：72.72 mm（274.9 px） 0.15：58.18 mm（219.9 px） 0.20：43.63 mm（164.9 px） 0.25：34.91 mm（131.9 px） 0.30：29.09 mm（109.9 px） 0.40：21.82 mm（82.5 px） 0.50：17.45 mm（66 px） 0.60：14.54 mm（55 px） 0.80：10.91 mm（41.2 px） 1.00：8.73 mm（33 px） 1.20：7.27 mm（27.5 px） 1.50：5.82 mm（22 px） 2.00：4.36 mm（16.5 px） 用法：把屏幕放在设定距离，让视标高度与上表一致，即可用于粗略自测或训练；屏幕 PPI 与浏览器缩放会影响 px 值，以 mm 值为准。 说明：自测结果不能作为医学诊断，视力异常请到眼科做专业检查。
A 1.0 acuity optotype subtends 5 arcminutes; at 6 m it is 8.73 mm tall, matching the international chart.
Frequently asked questions
What is the optotype formula?
The international standard sets a 1.0 acuity optotype to subtend 5 arcminutes at the test distance, so for acuity V the angle is θ = 5 / V arcminutes and the height is h = 2 × d × tan(θ / 2). Check: at V = 1.0 and d = 6 m, θ = 5′, so h = 2 × 6000 × tan(0.0416667°) = 8.727 mm — exactly the 8.73 mm of the 6/6 line on a standard chart.
Why is the 1.0 optotype only 7.27 mm at 500 cm?
Because optotype height scales with distance: 8.727 × (500/600) = 7.27 mm. That is why a chart must state its test distance; the same line changes size when the distance changes, and charts are not interchangeable.
Can I use the pixel values directly?
Only as a guide. The conversion assumes the CSS pixel definition of 1 px = 1/96 inch (96 dpi), while the real display PPI and browser or system scaling change the physical size. For accurate self-testing trust the millimetre values, or calibrate by measuring a 100 mm line on screen first.
What is the 20-20-20 rule?
Every 20 minutes of near work, look at something 20 feet away (20 × 0.3048 = 6.096 m) for 20 seconds. Plan mode lists each round's minute mark and cumulative rest, so five rounds means 100 minutes of work and 100 seconds of rest.
How does near-far training work?
Focus on a near point at 33 cm (the standard reading distance) for five seconds, then on something 6 m away for five seconds, repeated ten times per set. The point is to alternate the ciliary muscle between contraction and relaxation to relieve accommodative spasm; one or two sets a day is enough.
Can it replace an eye exam?
No. The tool does geometry and offers general eye-hygiene advice; it has no diagnostic ability. If self-testing shows reduced acuity, distortion or floaters, see an ophthalmologist.
Keywords：视力训练视标尺寸视力表20-20-20护眼eye trainingoptotype