👁️ 在线视力测试（E 字视力表）Online Eye Test (Tumbling E Chart)
在线视力自测：先用银行卡校准屏幕尺寸，按 5 米、3 米或 40 厘米等距离显示标准对数视力表上的 E 字，按开口方向作答，自动得出 5 分记录和小数视力；还有完整视力表和散光测试图。仅供参考，不能代替医院验光。Check your eyesight online: calibrate the screen with a bank card, then answer which way the E opens at 5 m, 3 m or 40 cm; you get a 5-point (logMAR) and decimal acuity. Includes a full chart and an astigmatism dial. A self-check only — not a substitute for an eye exam.
第 1 步：校准屏幕尺寸Step 1: calibrate your screen
拿一张银行卡或身份证贴在屏幕上，拖动滑块让下面的蓝色卡片和实物一样宽（85.6 mm）。Hold a bank card or ID card against the screen and drag the slider until the blue card is exactly as wide (85.6 mm).
“E” 的开口朝哪边就按哪个方向（电脑也可以用键盘方向键）。每一行答对 3 次即通过，答错 2 次结束。Press the direction the E opens toward (arrow keys work too). 3 correct passes a line; 2 wrong ends the test.
遮住一只眼，在约 1 米外看这张图。如果某个方向的线条明显比其他方向更黑、更清楚，可能存在散光，建议到医院或眼镜店做验光。Cover one eye and look from about 1 m. If lines in some directions look clearly darker or sharper than others you may have astigmatism — get an eye exam.
⚠️ 本测试只供自查参考，不能代替医院或专业验光。屏幕亮度、距离和校准都会影响结果。This is a self-check only and cannot replace a professional eye exam. Brightness, distance and calibration all affect the result.
使用说明与常见问题How-to & FAQ
「在线视力测试（E 字视力表）」是什么？What is the Online Eye Test (Tumbling E Chart)?
在线视力自测：先用银行卡校准屏幕尺寸，按 5 米、3 米或 40 厘米等距离显示标准对数视力表上的 E 字，按开口方向作答，自动得出 5 分记录和小数视力；还有完整视力表和散光测试图。仅供参考，不能代替医院验光。Check your eyesight online: calibrate the screen with a bank card, then answer which way the E opens at 5 m, 3 m or 40 cm; you get a 5-point (logMAR) and decimal acuity. Includes a full chart and an astigmatism dial. A self-check only — not a substitute for an eye exam.
如何使用「在线视力测试（E 字视力表）」？How do I use the Online Eye Test (Tumbling E Chart)?
第一步：把银行卡贴在屏幕上，拖动滑块让蓝色卡片和实物一样宽。第二步：选择测试距离并站到对应位置，遮住一只眼，点“开始测试”，看清 E 的开口方向后点对应的箭头（电脑可用键盘方向键，让旁人帮忙按更准确）。Step 1: hold a bank card to the screen and drag the slider until the blue card matches. Step 2: choose the distance and stand there, cover one eye, press Start and answer which way each E opens (arrow keys work; a helper pressing for you is more accurate).
视力 5.0 和 1.0 是什么关系？How do 5.0 and 1.0 relate?
国内常用“5 分记录”（如 4.8、5.0），国际常用小数视力（如 0.6、1.0），两者换算为：5 分记录 = 5 + lg(小数视力)。所以 5.0 = 1.0，4.9 ≈ 0.8，4.8 ≈ 0.6，4.7 = 0.5，4.0 = 0.1。China uses the 5-point scale (4.8, 5.0); elsewhere decimal acuity (0.6, 1.0) is common. 5-point = 5 + log10(decimal), so 5.0 = 1.0, 4.9 ≈ 0.8, 4.8 ≈ 0.6, 4.7 = 0.5, 4.0 = 0.1.
为什么一定要校准屏幕？Why must I calibrate the screen?
不同手机和显示器的像素密度不同，同样的像素在屏幕上的实际大小差别很大。用银行卡（标准宽度 85.6 mm）校准后，E 字才能按标准视角显示出正确的毫米尺寸。Pixel density differs between devices, so the same pixels have different physical sizes. Calibrating with a bank card (85.6 mm wide) lets the E be drawn at the correct size for the viewing angle.
测出来视力下降怎么办？My result is low — what now?
屏幕亮度、反光、距离不准都会让结果偏低，可以重测一次。如果仍低于 4.9（0.8），或者两眼差别明显，建议到医院眼科或正规眼镜店做专业验光检查。Brightness, glare and distance errors can lower the result, so retest. If it is still below 4.9 (0.8), or the eyes differ clearly, get a professional eye exam.
「在线视力测试（E 字视力表）」免费吗？文件会上传吗？Is the Online Eye Test (Tumbling E Chart) free? Are my files uploaded?
「在线视力测试（E 字视力表）」完全免费，无需注册。你输入的内容只保存在本机浏览器里（方便下次继续），不会上传到任何服务器。The Online Eye Test (Tumbling E Chart) is free with no sign-up. What you enter stays in this browser only (so you can continue later) and is never uploaded to any server.