Hi I had gone through your query. Spinal tap ruled out infection but there are many other cause beside infection that lead to headache with blurring of vision. Beside infection it could be trauma/vascular pathology/migraine/tension headache etc. Diagnosis depend upon clinical presentation. You need to investigate yourself. 1st thing is require is fundus examination. It will shows any papillodeama that suggest raise in interracial tension. MRI brain will helpful to rule out any pressure producing lesion or space occupying lesions. If all come normal then it may due to migraine or tension type headache. Consult neurologist or psychiatrist for better evaluation. I hope i have answered your query. Still if you have query then feel free to ask. Get well soon. Thank you.