Clym’s declining eyesight is a physical representation of his imperceptiveness. Clym has left Paris for Egdon, where he hopes to open a school despite lacking the necessary skills and funds. Numerous characters mention that Clym’s school is a bad idea, including Eustacia and Mrs. Yeobright, but he continues with the project anyway. Eventually, his studies put too much of a strain on his eyes, and he starts to lose his sight. This loss of sight represents a key trait of Clym’s character: that is, a lack of awareness of what is going on around him and a lack of concern for other people’s opinions.
Clym’s shortsightedness isn’t limited to his career—it also extends to his relationship with his wife. From the start, Eustacia makes her wishes clear to Clym: she wants to go to Paris. Despite this fact, and despite many warnings from his mother, Clym thinks he can make Eustacia happy in Egdon. Additionally, he is the last one to realize that Eustacia is secretly seeing Wildeve (who she’s in love with). In fact, there is very little information in the novel that Clym learns on his own. In this way, he stands in sharp contrast to someone like Mrs. Yeobright or Venn, who are generally quite perceptive. The fact that Clym is losing his eyesight while all of this is going on emphasizes just how undiscerning he is—he’s both figuratively and literally shortsighted.