Eye pattern is a pattern displayed on the screen of a cathode ray oscilloscope (C.R.O).

The shape of this pattern resembles with the shape of human eye.

Therefore it is called eye pattern.

Eye pattern is a practical way to study the intersymbol interferences and its effects on a PCM or data communication.

The eye pattern is obtained on the C.R.O. by applying the received signal to vertical deflection plates(Y-plates) of the C.R.O. and a sawtooth wave at the transmission symbol rate i.e. (1/Tb) to the horizontal deflection plates(X-plates) resulting display is eye pattern as it resembles human eye.

The interior region of eye pattern is called eye opening.