Eyes
Throughout the novel, the eyes are a symbol of the sincerity and kindness of an individual. Paul gets worried when he sees Hayt with mechanical eyes. Despite knowing that Hayt has come from Duncan Idaho, Paul's trusted master, he feels that something bad is about to happen. In other words, Paul does not trust Hayt because he might be planning something sinister. Paul's prescience tells him that anyone without human eyes poses a looming danger to his empire.
Melange
In the novel Dune Messiah, Melange symbolizes authority and its negative effects. Melange is an addictive drug that everyone depends on. Therefore, whoever controls the supply of the drug rules the world. When Paul rises to power, he controls the supply of the Melange drug, meaning that the world worships him. However, when Paul starts using the drug, he starts losing his prescience ability to foresee the future, and this threatens his ability to control any uncertainty that can threaten his leadership.
The Dune (Arrakis)
The Dune is a symbol of transformation. When Paul takes power, the Dune is entirely covered by sand. However, after becoming the Emperor, Paul orders his people to plant vegetation on the Dune, which slowly turns green. The Dune becomes beautiful and is declared the capital city (Arrakeen). The capital is quickly filled with modern architectural buildings, temples, freeways, and flyovers. Consequently, the Dune symbolizes the possibility of transforming anything into a desirable outcome.
