When descending in an airplane i get terrible pressure behind my eye. what can i do to stop this?

Check the sinuses: The transient pressure felt behind the globe and in the face area is usually due to pressure changes and the sinuses. Sometimes, sinus congestion prevents equalization of the pressure between the sinus and outside. Decongestants can help but the best thing is to see your primary care doctor if this occurs frequently.

Pray: Hold your nose and blow air through your ear.