Many eye diseases can cause headaches, even severe ones. Headaches caused by eye diseases are called ophthalmogenic headaches, such as refractive and regulatory abnormalities, ocular muscle balance disorders, glaucoma, iridocyclitis, keratitis, ocular and orbital infections, and cancer can cause headaches. The nerves in the eye are quite abundant, including the optic nerve, trigeminal nerve, motoneurotic nerve, talocrural nerve, and sympathetic nerve of the abducent nerve. Among them, the eye is innervated by the ciliary nerve, which is divided into the long ciliary nerve. The ciliary long nerve is the branch of the 5th pair of cranial nerves, the first ophthalmic branch of the trigeminal nerve, while the ciliary short nerve has 6 to 10 nerves originating from the ciliary ganglion, which is composed of the trigeminal nerve and the sympathetic nerve of the motor nerve. The ciliary ganglion is located deep in the orbit, enters the eye around the optic nerve, and is the main conduction nerve for ocular sensation. The first ophthalmic branch of the trigeminal nerve is a purely sensory nerve, distributed in the cornea, iris, and upper eyelid of the ciliary body of the eye. Because of the abundance of nerve fibers in the ophthalmic branch and its sensory sensitivity, lesions in these areas can cause severe pain. In contrast, the sensation of the conjunctiva of the lower eyelid is innervated by the second maxillary branch of the trigeminal nerve. Therefore, when the eye is affected by diseases of different nature, the nerve endings innervating the eye are often stimulated and damaged, causing eye pain and headache. Refractive and regulatory abnormalities are the most common types of eye diseases that can cause headaches. Patients with refractive and regulatory abnormalities such as hyperopia, myopia, astigmatism, presbyopia and ciliary spasm often have headaches of varying degrees. This is because the ciliary muscles must be tense and constantly adjusted to ensure clear vision, especially during prolonged use of the eyes, and the constant and excessive adjustment of the ciliary muscles can easily cause headaches. The characteristics of headache in this type of patients are related to the use of eyesight, and the longer the time of seeing, the heavier the headache; if the eyes are closed and rested, the headache can gradually reduce or disappear. The headache is usually located in the orbit, frontal region and temporal region, and sometimes it can be radiated to the occipital region or even the whole head, and when the headache is severe, it can be accompanied by nausea and vomiting. Due to prolonged headache, patients may have neurological symptoms, such as emotional instability, insomnia, memory loss, etc. One of the clinical manifestations of glaucoma, a common eye disease that seriously endangers vision and can cause blindness, is eye pain. One of the clinical manifestations of glaucoma is pain in the eye. The pathogenesis of glaucoma is mainly the impairment of atrial fluid circulation, which leads to a sharp rise in intraocular pressure and causes headache. Under normal conditions, the production and discharge rates of atrial fluid secreted by the ciliary muscle are in a dynamic balance, which is an important factor in maintaining normal IOP, but if this dynamic balance is out of balance, excess atrial fluid is formed or the outlet of atrial fluid is blocked, it will lead to an increase in IOP. When the IOP rises more than 8mmHg in 24 hours, the high pressure exceeds 21mmHg or the difference between the two eyes is 5mmHg, it should be considered abnormal. When IOP rises to 50-80 mmHg, glaucoma has an acute attack, and the eye is as hard as a rock when finger pressure is applied to the upper eyelid. If not treated urgently, it can easily lead to rapid blindness. Almost all acute and chronic glaucoma is associated with headache, and headache due to glaucoma is usually persistent and severe on the sick side or worsens in paroxysms. The pain is initially located in the orbital region of the eye, but may progress to the laminae of the first branch of the trigeminal nerve in the frontotemporal region. The onset of the headache may be triggered by emotional stress, trauma, overexertion, sudden climatic changes, and overeating. Most of the patients have nausea and vomiting. In addition to headache, most of the patients have iridescence before the onset of the attack, i.e., they see a “rainbow ring” around the light. After an acute attack, the patient has a dramatic loss of vision in the eye on the side of the disease, or in severe cases, only a sense of light in front of the eyes, photophobia, lacrimation, corneal edema and cloudiness, and congestion around the eye. Funduscopic examination sometimes reveals congestion of the optic papillae and dilated veins, sometimes making it impossible to see clearly. Finger-prick testing may reveal elevated intraocular pressure in the affected eye, with the eye as hard as a rock. The headache is severe, swelling or burning pain when the intraocular pressure rises sharply. This is accompanied by significant ocular changes and symptoms such as fever, chills, diarrhea, and constipation. These acute congestive glaucoma attacks can raise intraocular pressure to 70 or 80 mmHg or more, often with severe eye pain and headache, accompanied by eye redness, vision loss, nausea and vomiting. Many patients’ first visit is often to a gastroenterologist or neurologist, leading to delays. In this case, emergency treatment in ophthalmology is needed to lower the intraocular pressure with medications, improve the water circulation in the eye, and save the visual function. If necessary, emergency surgical treatment is required. In chronic glaucoma, the headache is the same as in acute glaucoma, but the symptoms are slower, and due to the chronic increase in intraocular pressure, the symptoms are often mild eye swelling and acidity with headache. As time lengthens, the eye gradually adapts to the elevated IOP, and the discomfort such as eye swelling and headache can disappear on its own. As a result, the disease is often delayed, and the condition is often advanced when the vision is significantly reduced. Therefore, the most important thing in daily life for glaucoma patients is to follow the doctor’s instructions to protect their eyes, and once they find eye discomfort, they should seek medical attention immediately to preserve their vision. In short, headache caused by eye disease has two characteristics: first, there is eye pain first, and the condition turns dramatic before radiating to the head, most of them are caused by acute inflammation of the eye or glaucoma; second, there is no pain when the eye is not used, and the pain appears after seeing near or distant objects, and the headache decreases when the eye is closed for a nap. If you suffer from headache and have the above characteristics or various medical treatments still do not improve, you should promptly go to the ophthalmology department to have your eyes checked.