Como eu respondi em a esta pergunta:
Uma citação de Aragorn, A Irmandade do Anel, Uma Faca no Escuro:
For the black horses can see, and the Riders can use men and other
creatures as spies, as we found at Bree. They themselves do not see
the world of light as we do, but our shapes cast shadows in their
minds, which only the noon sun destroys, and in the dark they perceive
many signs and forms that are hidden from us: then they are most to be
feared. And at all times they smell the blood of living things,
desiring and hating it. Senses, too, there are other than sight or
smell. We can feel their presence - it troubled our hearts, as soon as
we came here and before we saw them; they feel ours more keenly. Also,
the Ring draws them.
Da história da Terra Média, O Retorno da Sombra, "De Gollum e o Anel", descrevendo o que acontece quando alguém é totalmente possuído pelo Anel:
Yes, if the Ring overcomes you, you yourself become permanently
invisible - and it is a horrible cold feeling. Everything becomes very
faint like grey ghost pictures against the black background in which
you live; but you can smell more clearly than you can hear or see. You
have no power however like a Ring of making other things invisible:
you are a ringwraith. You can wear clothes. (you are just a
ringwraith; and your clothes are visible, unless the Lord lends you a
ring) But you are under the command of the Lord of the Rings.
O fato de serem cegados pela ganância é realmente figurativo, mas tem uma aplicação real. Sua ganância pelo poder de Sauron os escravizou ao ringue, o que os levou a se tornarem espectros. É por isso que eles não podem ver bem. Então eles estavam literal e figurativamente cegos pela ganância.