Although it is relatively uncontroversial to characterize all Platonists as metaphysical idealists or immaterialists, the ascription to some of them of explicit arguments for epistemological idealism is controversial and problematic. It will be necessary to consider Neoplatonic attitudes toward perception of an external material world, but also the direct intellectual "perception" of the Forms.
Bussanich, John, "Were the Neoplatonists Itealists or Realists?" (1992). The Society for Ancient Greek Philosophy Newsletter. 177.