This line signals us that the story is concerned with how people form opinions and acquire knowledge from popular culture. It also cautions against generalizations. There is no "typical" blind person any more than there is a typical sighted person.
On her last day in the office, the blind man asked if he could touch her face. (1.2)
Ironically, the image of a blind person touching a person's face to see what the person looks like is a popular one in movies, TV, and even stories (like this one). Carver is drawing from these sources in creating his portrait of Robert, and reminding us that "Cathedral" is a story.
"Are you crazy?" my wife said. "Have you flipped or something?" She picked up a potato. I saw it hit the floor then roll under the stove. (1.12)
She isn't far from the truth. Jealousy, insecurity, and communication problems distort the narrator's reality. His distorted reality makes his wife angry, and makes her husband seem like a more closed-minded person than he actually is.
Imagine a woman who could never see herself as she was seen in the eyes of her loved one. (1.15)
Even though these lines are part of the narrator's most bitter thoughts, there is some truth in them. We would never agree that the woman's value is in any way diminished because Robert can't see her. Rather, we suggest that our realities are constructed around both what we see and how we think we are being seen.
My eyes were still closed. (3.40)
In the final moments of the story the narrator sees reality in a new way, by giving up his belief that sight is the most important way to process and create reality.