Csar and Think first- If I may answer for Sam2, I dont think he means physical pleasure per se. He means you are you using the physical- your eyes- to have a hanaah. It clearly says “Hamistakel” looking, which is explained as looking for the purpose of pleasure. Touching for enjoyment without looking is assur, but not because of Hamistakel etc..
If you would dream about an etzbah ktana that you never saw you wouldnt be oiver on hamistakel either.