Microphthalmia is a big word that describes when someone's eyes are smaller than they should be. Think of it like a toy that doesn't work the way it's supposed to: if the eyes are too small, it can be hard to see things clearly.
This can happen for different reasons, but some people are born with microphthalmia and others may develop it later on. People with microphthalmia might have trouble seeing things that are far away, or they might have trouble seeing things up close. Sometimes they might need to wear glasses or contacts to help them see better.
It's important to talk to a doctor if you or someone you know has microphthalmia, because they can help find the best ways to make sure the condition doesn't cause any long-term problems.