Tension Headache: This is the most common type of headache and can cause pain behind the eyes due to muscle tension in the face and neck.
Sinusitis: Inflammation of the sinuses can cause pain behind the eyes, especially if the ethmoid or frontal sinuses are affected.

Migraine: A migraine can cause severe, unilateral pain that may be felt behind the eye, often accompanied by sensitivity to light and sound.
Cluster Headache: These are severe headaches that occur in clusters or cycles and are often felt on one side of the head, behind the eye.
Dry Eye Syndrome: Irritation and inflammation of the eyes can cause pain behind the eyes, especially if the eyes are dry and irritated.
Refractive Errors: Uncorrected vision problems, such as nearsightedness or farsightedness, can cause eye strain and pain behind the eyes.

Giant Cell Arteritis: This is an inflammation of the blood vessels in the head that can cause severe headaches, including pain behind the eyes, and can lead to blindness if not treated promptly.
Temporal Arteritis: Similar to giant cell arteritis, this condition can cause pain behind the eyes and can lead to serious complications if not treated.
Brain Tumor: Although rare, a brain tumor can cause headaches, including pain behind the eyes, and is a critical diagnosis not to miss.
Acute Angle-Closure Glaucoma: This is a medical emergency that can cause severe eye pain, including pain behind the eyes, and can lead to blindness if not treated promptly.

Trigeminal Neuralgia: A chronic pain condition that affects the trigeminal nerve and can cause severe, shock-like pain behind the eyes.
Idiopathic Intracranial Hypertension: A condition characterized by increased pressure in the brain that can cause headaches, including pain behind the eyes.
Cavernous Sinus Thrombosis: A rare condition that can cause pain behind the eyes, as well as other symptoms such as double vision and drooping eyelids.
Optic Neuritis: Inflammation of the optic nerve that can cause pain behind the eyes, especially with eye movement.