In his indispensable Reader's Guide to Remembrance of Things Past ((1984) translator Terence Kilmartin devotes a 12-line entry to the topic of "monocles." I find fully a dozen characters whose lives are enhanced, clarified or otherwise made this little sliver of glass.
Some are straightforward. Baron de Charlus, perhaps the most interesting (male) character in the book, has the least problematical monocle; it is just there. (II: 278) Mme de Verdurin (newly redefined as the Princess de Guermantes, at least get to use hers: She "fixe[s] her great monocle in her round eye, with an expression half of amusement, half of apology for her inability to sustain gaiety for any length of time ... " (III: 1033)
Monocles come in a variety of shapes and sizes. Thus the Marquis de Foresetelle's is "minute and rimless...like a superfluous cartilage the presence of which is inexplicable and its substance unimaginable." (I:356) But M. de Saint-Candé's "encircled, like Saturn, with an enormous ring, was the center of gravity of the face.." (I:356)
Other monocles have more complex assignments. General de Frobervilles's is "stuck between his eyelids like a shell-splinter ... a monstrous wound which it might have been glorious to receive but which it was indecent to expose" (I:355). M. de Bréauté sports his "as a festive badge...[it] bore, glued to its other side, like a specimen prepared on a slide for the microscope, an infinitesimal gaze..." (I:356); his "smiles [come] filtered through the glass of his monocle" (II:447); cf. (II:679). But Mr. Palancy, with "his huge carp's head ... had the air of carrying about upon his person only an accidental and perhaps purely symbolical fragment of the glass wall of his aquarium..." (I:356-7); cf. ( II: 39): "unconscious of the press of curious gazers, behind the glass wall of an aquarium."
But in others, there is a sometimes-subtle shift to a more unsettling role. Thus,
The Marquis de Cambramer's monocle "protect[s], like the glass over a valuable picture," a deformity in his eyeball. (II:1101) Protects? Granted we may be observing a mere passive instrumentality, but it is hard to escape the suspicion that it may be the monocle itself engaged in the act of protecting.
So also, the duc de Guermantes:his monocle has a "gay flash" (II:49) We can accept the "flash" as as reflection of the sunlight, but in what sense is the monocle "gay"? If this seems too picky; note that few pages earlier we were told tht the monocle is "quizzical." (II:27). Quizzical? So also Swann's monocle. Odette finds it "tremendously smart" (I:268). Swann removes it "like an importunate, worrying thought ... from whose misty surface, with his handkerchief, he sought to obliterate his cares" (1:377-8). Worrying? The Monocle has his cares?
Two other monocles exceed all others in their purposeful activity. First, consider Marcel's old friend, Bloch: "By introducing an element of machinery into Bloch's face [his] monocle absolved it of all those difficulties which a human face is normally called upon to discharge, such as being beautiful or expressing intelligence or kindliness or effort. The monocle's mere presence even absolved an interlocutor ... from asking himself whether the face was pleasant to look at or not... [B]ehind the lens of this monocle, Block was newly installed in a position as lofty, as remote and as comfortable as if it had been the glass partiation of a limousine ..." (III: 996)
And if he monocle engaged in the act of absolution is not enough, consider at last the most active, the most playful, the most alive of all monocles--a monocle with at least as much character as its owner himelf. That would be the monocle of Marcel's friend Robrt St. Loup, who "strode rapidly across he whole width of the hotel, seeming to be in pursuit of his monocle, which kept darting away in front of him like a butterfly." (I: 783-4). Later it "resume[s] its gambolings on the sunlit road, with the elegance and mastery which a great piaanist contrives to display in the simplest stroke of execution..." Elsewhere we have "...his monocle spinning in the air before him..." (II: 68)
I think there may be a more pervasive point underneath all this frivolity. Start with one clear principle: Proust is a very funny writer--sometimes and earthy or a bawdy writer with a sense of the absurd that could come straight out of a Feydeau farce. Moreview Proust acquired a lot of his world-view from his near-contemporary, the philosopher Henry Bergson. For Bergson, comedy was a person acting like a machine. There may be more to it than that; others have suggested that you can make comedy when a machine acts like a person.
Once you think about Proust in this context, you find suggestive examples everywhere. Madame Cambramer, seeking to impress on those around her that she has an appreciation for great music, undertakes to bob her head back and forth like a metronome; but her diamond earrings snag in her bodice show show she has ceaselessly to rearrange herself, all the time seeking not to miss a beat. Berma in Phèdre is a branch of coral in an aquarium (M. de Palancey's?) (I:732) Marcel remembers Albertine the cyclist "speeding through Balbec on her mythological wheels" (II: 498) ((Kilmartin gives eight lines to "bicycles"). Marcel disgraces Aunt Léonie's sofa by losing his virginity on it; he disgraces his beloved grandmother's sofa by presenting it to a brothel. The 1.22 train to Normandy is "fine, generous." (I:418-19) The aeroplane over Versailles is a "little insect." (III:413). And so it goes. In a world like this, for a man to be led around by his monocle is a small matter indeed.