Guinea pigs do blink. It is rare to see these small rodents blink, or even sleep with their eyes closed, but they occasionally clear their eyes with their eyelids.
Guinea pigs have different eyes than those commonly found on other mammals, and the structure of the animals' eyes prevents them from needing to blink frequently to clear their eyes of dust. Guinea pigs' eyes have a larger-than-normal aqueous humor, which is a transparent fluid covering their eyes, that prevents small debris from drying out or otherwise irritating them. The result is that the rodents have less of a need to blink, and this also helps them in the wild. As prey animals, wild guinea pigs must possess a constant awareness of threats around them, so they sleep with their eyes open to appear awake and alert to possible predators. Their unique eye structure has evolved to serve a survival purpose even though it is not needed for their domesticated counterparts.