幻眼管（Magic Eye，亦称猫眼管）是一种热真空电子管，用来给出音效输出、信号强度或其他功能的视觉信号，于约1936年之后加入收音机的设备之中，替代较早的 Tuneon 霓虹灯调谐指示器。实际上，幻眼管是一种微型的阴极射线管，通常会发出绿光，且屏幕上未发光的部份在调准到和发射台同频时会变窄，因而显示出信号的「高峰」。幻眼管的使用目的即在于帮助调至最强的发射台频率。幻眼管在视觉上的帮助使得信号强度比起单独用耳朵要来得容易量测得多。

当1950年代早期，FM收音机开始在英国市场上出现时，许多态式的幻眼管也跟着出现。虽然有许多不同的外观，但运作原理都是一样的。一些幻眼管甚至有分别的小屏幕来显示FM的立体声多路传输接收。

A magic eye indicator, called in technical literature an electron-ray indicator tube, is a vacuum tube which gives a visual indication of the amplitude of an electronic signal, such as an audio output, radio-frequency signal strength, or other functions. It is also called a cat's eye, or tuning eye in America. Its first broad application was as a tuning indicator in radio receivers, to give an indication of the relative strength of the received radio signal, to show when a radio station was properly tuned in.