Hi there and welcome,
What your brain MRI is saying is that you have a lot of tiny sized lesions, typically only 1-3mm are left unmeasured on MRI reports, and micro size non specific white matter lesions would be consistent with microvascular disease, which is the most common cause.
Microvascular disease is not typically related to brain surgery but microvascular disease is unlikely to account for the types of symptoms you are having...
Headaches are classified into two categories either primary and secondary, primary headaches include migraine, tension-type, and cluster headaches typically have no apparent underlying organic disease process but secondary headaches are caused by an underlying organic disease and are a symptom of a recognised disease process and patients with frequent or severe headaches usually require evaluation of any serious condition that may be causing the headache.
Fainting or syncope can be caused by dehydration, medications, diabetes, pregnancy, anemia, heart conditions, age etc Dysthymic disorder, is a mild but chronic type of depression but its your ocular pain (left eye) and persistent degrading vision in the same eye that imho is a heads up to the potential of something like optic neuropathy or an ocular disorder especially retinal disease and may be the clue to working this out for you. So with that thought in mind i would highly recommend you see an ophthalmologist and get the health of your eyes checked and if you already have, get a second opinion and depending on your visual findings it should help rule in or out all the types of the associated medical conditions and provide you with some alternative directions...
I hope that helps......JJ