Headaches can be due to innumerable causes and visual problem is just one of them. Other common causes for headache are tension headache and migraine. Other associated features help in making a proper diagnosis. Consult a psychiatrist/neurologist with details like frequency, aggravating/relieving factors and sleep patterns.

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Firstly show your daughter to an Ophthaomologist at a Hospital. Maybe there is some problem in the eyes like high pressure which is causing pain. If the Ophthalmologist says her eyes are not the cause of the headache then she needs to see a Neurologist to rule out Migraine which is severe one sided headache with vomiting and seeing lights and colours, or any brain masses which is causing pain. How old is your daughter. She can take a pain killer over food under medical supervision for the headache in the time being.