Coffee Causes Temporary Blindness

A brother I haven't seen in some years is visiting.  He's a rough & tumble Arizona rancher, who also does work in Africa and Pakistan.
I was astounded to hear hiim say that he can't drink coffee because it makes him go completely blind for a half hour or so.  It happens every time he takes even a sip of coffee.  The only kind of coffee that doesn't affect him this way, he says, is Somali coffee, which is made from the coffee bean husk instead of the bean.  Drinking any kind of tea is absolutely no problem for him.
Has this symptom ever come up before?  It seems to me, this would be worth further study.  And no, he's not "pulling my leg..."

[John C Hagan III, MD, FACS, FAAO]

I have never had a patient complain of this, nor I have I ever read about a similiar complaint in the medical journals. Some patients use coffee to break or abort a migraine headache while others have found that coffee can cause a miagraine. The only thing I could think is that he has a form of ophthalmic migraine with coffee as a "trigger".  

JCH III MD Eye Physician & Surgeon