The eyes can give away an opponent's intent.... but they can also be used to deceive.
As a former hockey player, we were coached to always look at the chest when defending, because to look at the puck or face would give the other guy a good chance to trick you with a fake. Look at his chest and hit him was the idea.
That said, when I spar I like to engage the opponents eyes (I've been told not to before). But I find most opponents will give away more strategy with their eyes than they will deceive you with them, but I remain very cognizant of the possibility. This awareness is the key, to me.
As my training is based more on defending in real situations and not squared-off fighting per se, body language and visual cues are of utmost importance.
This said, being cognizant of your own cues is also immensely important. You may give away your own attacks with your visual focus, so not telegraphing is important, unless of course it is being used deliberately to misguide your foe. Football quarterbacks are excellent at this--looking at one receiver and then throwing the ball to someone in another location. But a QB who telegraphs his throws gets picked off routinely, and his receivers get very sore and disgruntled.
It's something to look into, anyway.