Good question. Anything that causes eye pain or that can risk further injury to the eye should be avoided. If the injury required suturing, there can be a risk of sutures breaking from bearing down. It is advisable to ask the doctor who treated you for your specific injury what level of activity you can engage in safely.
Depends on injury. If you have a hyphema or bleeding in the eye or a traumatic posterior vitreous detachment you need rest - not sexual activity. We get concerned about rebleeding in injury and sexual activity opens the possibility of eye trauma (it usually is shielded post injury) and increased blood pressure. Wait until you're healed then have fun!