Dear Vamsi,
Typically, when no noise in the system and all used devices are ideal, there will be a clean eye with no amplitude or jitter present in the eye. However, depending on the noise sources in the transmission system starting from the laser, the modulator, channel characteristics, and detector, there will be noise on the one and zero levels (amplitude noise) and jitter that distorts the eye and may close it.
Regards,
Ahmad