Tension Headache: This is often the most common cause of headaches and can be associated with blurry vision due to tension in the muscles around the eyes. It's typically characterized by a band-like pressure around the forehead, back of the neck, or both.

Migraine: Migraines can cause severe headaches and are often accompanied by visual disturbances such as blurry vision, sensitivity to light, and sometimes aura symptoms like zigzag patterns.
Dry Eye Syndrome: This condition can cause eye strain leading to headaches and blurry vision due to insufficient lubrication of the eyes.
Refractive Errors: Uncorrected or under-corrected vision problems like myopia, hyperopia, or astigmatism can lead to eye strain, resulting in headaches and blurry vision.
Sinusitis: Inflammation of the sinuses can cause headaches and, if the sinuses around the eyes are affected, may lead to blurry vision due to swelling and pressure.

Giant Cell Arteritis: Although less common, this condition is critical to diagnose early because it can lead to blindness if not treated promptly. It typically presents with headaches, visual disturbances (including blurry vision), and jaw claudication.
Stroke or Transient Ischemic Attack (TIA): Sudden onset of headache and blurry vision could be indicative of a stroke or TIA, especially if accompanied by other neurological deficits like weakness or speech difficulties.
Brain Tumor: A tumor in the brain can cause increased intracranial pressure, leading to headaches and visual disturbances, including blurry vision.
Idiopathic Intracranial Hypertension (IIH): Characterized by increased pressure within the skull without a detectable cause, IIH can lead to headaches and visual symptoms, including blurry vision and double vision.

Multiple Sclerosis: An autoimmune disease that affects the brain and spinal cord, multiple sclerosis can cause a wide range of symptoms, including vision problems and headaches, though it's less common as a primary presentation.
Optic Neuritis: Inflammation of the optic nerve can cause pain with eye movement and blurry vision, often associated with headaches.
Papilledema: Swelling of the optic disc due to increased intracranial pressure can cause transient blurry vision and is often associated with headaches.