Differential homonymous visual loss

Occipital Stroke (especially PCA,may be heralded by episodes of vision blurring or dimming with flickering. May itself indicate onset of MI or atrial fibrillation and EKG should be checked

Abnormal MRI
Tumors
Hemorrhage
Radiation damage
demyelinating diseaseinfections (especially PML)
MELAS (mitochonidrial encephalopathy with lactic acidosis and stroke like syndromes)
reversible posterior leukoencephalopathy (associations include eclampsia, preeclampsia, hypertensive encephalopathy, acute glomerulonephritis, porphyria, seizures, and numerous immunosuppressive drugs)Normal MRI (or at least normal in occipital area)
Jacob-Creutzfeld disease
Alzheimer's disease
nonketotic hyperglycemia