It's very interesting, the etymology behind this, because it can be very easily explained, if you'll read me.

When the body experiences a headache, it is due to the dilation of the blood vessels in the brain; essentially, the blood vessels open up wider than normal, and press against nerves surrounding the brain and skull, because the brain itself cannot feel pain.

The same thing is going on with your eyes- the blood vessels are dilating and pressing against your ocular nerves in excess. Glaucoma patients have trouble with blood pressure behind their eyes, and smoking pot helps widen the blood vessels in order for the blood to have more room to flow around, and thus regulating the ocular blood pressure, reducing any possibility of damage to the eye or ocular nerve.

In simple terms, lay of the pot for a bit, and drink caffiene- this will help return the blood vessels to their normal size