Pyrex vision is a phrase often used by rappers in their song's lyrics. Pyrex is a brand that produces many household glassware, including some that drug dealers often use to cook crack cocaine. When rappers say pyrex vision, they're signaling that they are drug dealers, the phrase comes from the fact that the utensil is made of glass and they can look through the Pyrex glass to see their product being cooked.
Though individuals saying 'pyrex vision' often mean they are drug dealers, it can also mean they have a vision of becoming drug dealers. Since pyrex is tied to crack, they mean they have a vision of becoming rich off selling drugs, more specifically crack. Someone saying 'Pyrex Vision' could also mean they are high.
As a side note, Pyrex Vision is also a brand of clothing.
In The Diplomats' 'Dipset Anthem' song, Juelz Santana said, "Back to the kitchen, that pyrex vision - Pop, I let that white stuff sit in - Get hard, get rock, get to the block and pitchin". In Dr Dre's 'It's Alive' song, Kendrick Lamar said "I rap with a Pyrex - In the projects - I'm crack in a pot".