If your eyes are tired, does it always mean that your body is also tired?

Not necessarily: Tired eyes are usually either (relatively) dry or strained from extended staring (reading a book or using the computer without a break for extended periods of time). You can be perfectly awake and alert, but the eyes may feel differently. Your eye doctor can evaluate your vision and set up a plan to control the symptoms better.

Tired: Not always. Your eyes may be tired from long periods of computer use or reading. At the same time, your body may be tired also, or it may feel plenty of energy.