Studies associate headache and other asthenopic symptoms with errors in refraction and vergence but there is no strict scientific evidence of causation. There is also little evidence that refractive or vergence error correction can alleviate headache. ICHD-3 contains diagnostic criteria for headache associated with refractive error, but at the same time it mentions that the prevalence of such headache is likely overestimated. It is recommended to assess more likely causes of headache first and to bear in mind that vision loss or strabismus that occured for the first time in association with headache is a red flag and secondary causes must be excluded. Despite the lack of scientific proof, most studies suggest that ophthalmologic assessment is indicated for patients with asthenopic symptoms or headache associated with visual tasks and the correct treatment of visual errors can help some patients with their headache.