Couple of years ago, while drawing in Greek hall of the Metropolitan museum I observed that edge of the hall's ceiling had bulging distortion. So, I assumed that my eyes' lenses have bulging distortion, similar to one of a photo-lens.Year later, drawing at Madison Park, I observed that distortion is more complicated than a simple barrel distortion. See images attached below. I
My final conclusion is that distortion is indeed caused by our eyes' lenses.
It is easier to observe if you close one eye and look to the sides. You'll notice that edges of tall straight structures are curved.
Our brain averages out information from both eyes, sometimes giving priority to one eye or another, that is why I saw difference in buildings' curvature.