In a lot of cases the eye diagram is the measure of compliance for signal on a channel. Reflections in our channel can impact or decrease the eye height. Whereas, the channel is also an attenuator of signal’s high frequency content, this means that the edge rate seen at the receiver is slower (or has a reduced slew rate) which can reduce your eye width. So for faster data rates we need faster slew rates (edge rates) to achieve an open eye at the other end of the channel.