What is astigmatism, the condition YouTuber MrBeast suffers from?

World's most subscribed YouTuber MrBeast revealed that he has astigmatism. It's a common eye problem that can make vision blurry or distorted. It happens when cornea or lens has a different shape than normal. The most common symptoms are blurry vision, needing to squint to see clearly, headaches, eye strain and trouble seeing at night.