They don't design them from scratch, but they DO participate in sensor design. That's part of the reason why wide angle Leica lenses don't suffer from terrible

They don't design them from scratch, but they DO participate in sensor design. That's part of the reason why wide angle Leica lenses don't suffer from terrible vignetting, corner smear and peripheral color shifts when used with Leica bodies. Leica uses offset microlenses to counteract those effects.