Often times, the GP will order an MRI before the initial visit with the neurologist. That way, major problems can promptly be ruled out and the neurologist will have more information to help you at the time of your visit. The down side to this is that the MRI will not necessarily be done with the same protocols that the neurologist would use, and the MRI will probably not be read by the same radiologist that the neurologist would have used. If you are worried then maybe you can talk to your GP and find out if the GP can order an MRI.
It would also be a good idea to schedule an appointment with an ophthalmologist, who may also order an MRI. In general, I have found that ophthalmologists don't take as long to get in to see as a neurologist. Neurologist take forever to see!
I have a suggestion that might be worth trying. Call the optometrist who gave you the referral and explain the situation. It might really help if he were willing to set up the appointment with the neurologist for you. (If you had seen an ophthalmologist, I think you could get the appointment within a few days. Hopefully, an optometrist can get some preferential treatment, too.)
I'm wondering about a possible diagnosis of psuedotumor cerebri - most common in overweight, younger females with headaches. Just a thought. Regarding your appointment, I'm sorry but I see it all the time too and I get a little frustrated. I totally understand your worries and the longer the wait the more you worry. That's completely normal. Your problem is not new and has been going on for months but it would be nice to at least have the MRI in a day or two - that's what I would want. Then you could rule out major intracranial problems but would not rule out pseudotumor cerebri. Good Luck - call again to maybe get appointment moved up.
MJK MD