Your description regarding your fathers health suggests multiple neurological lesions. Ischemic foci means that the blood flow to the brain tissue is absent at those points. Age related cerebral changes are common in old age. The are due to degeneration of brain tissue due to multiple factors of them the commonest is cummulative oxidative/free radial stress
to the brain tissue.
These lesions can affect your fathers vision but mostly that tends to produce similar involvement of both eyes. Any blurring of vision related to only one eye will have the pathology most likely in the same eye or its nerve
. I strongly suggest you to consult the ophthamlologist or preferably a neuro-ophthalmologist to help you look for the probable cause of decline in vision. Take care