As usual, this Spanish saying is not used for its direct translation, which is “can’t see three (people) on a donkey”. This expression is used to explain that you, or someone else has terrible eyesight. It is very similar to the english expression “blind as a bat”. The saying comes from the very old and rural method of testing a persons eyesight. The patient would be shown various drawings and would be required to describe what they see! If you wear glasses, you can say “Sin gafas no veo tres en un burro” (Without my glasses I can’t even see 3 people on a donkey!).
Your friendly neighbourhood travel guide,