Essentiallly the MRI is telling you that your brother has chronic under-treated high blood pressure
with resultant vascular damage --- reflected by the prior stroke and microvascular changes.
The transient double vision coupled with and episode of high blood pressure suggests a vascular occlusion in the brain stem.
The only treatment is to control all vascular risk factors including high cholesterol
, diabetes, and blood pressure. The carotids should be checked for obstruction to determine if additional anticoagulation or endarterectomy
is indicated to reduce the risk of stroke. In your brother's case, there is occipital lobe
damage from prior stroke. Since this portion of the brain is fed by the posterior cerebral arteries
, MR angiography can also be performed to check for obstruction in these arteries to likewise determine if anticoagulation is indicated.