If you're not really familiar with Family Guy humour, I guess I'll have to explain the joke to you.
See, the hilarity of this is the convergence of two polar opposites. The concept of a cartoon villain undertaking a mundane activity like an eye exam forces the viewer to examine their assumptions of the unexamined routines of characters.
The monotony of the activity juxtaposed with his ridiculous appearance is what makes this instance unique, and if your humor is so inclined, funny.
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