There are different grades of progressive lenses as well, if it's for your livelihood go for Varilux lenses,
Varilux multi-focal lens range | Essilor Singapore
The distortion is much lower and you can get transitions which darken in sunlight and clear indoors. In a decent frame, the price will take your breath away but when I go for my medical I'm glad I paid the extra.
Cheaper lenses are available but the degree of distortion is higher.
BTW I found an optician in India who will change the lenses on my reading glasses for $4, quality is quite acceptable so I'm taking a few old frames to him next month so I can have a few spare pairs lying around.