The that looks like frosting along the vessels is a perivenous lymphocytic infiltration. Sometimes called "sheathing," it betokens a vasculitis.
Retinal vasculitis occurs in sarcoidosis, Behçet's Disease, multiple sclerosis, and in idiopathic conditions. But contrary to popular opinion, it is extremely rare in connective tissue disorders such as lupus. Instead, connective tissue diseases produce multiple bland occlusions appearing as cotton wool spots, branch retinal artery occlusions, and obliterative vasculopathy.