[allegory]

Anecdote. I had a 2011 MBP with backlit keyboard. Never used it once. In fact, the machine ended up with windows on it because MacOS made me want to smash the thing (despite being a Unix guy) and the Boot Camp drivers didn't switch the backlight off reliably which annoyed the crap out of me.

If you're sitting in a place dark enough to need it, it's not good for you staring at the contrast between the screen and darkness so turn the light on.

Plus I don't look at the keyboard anyway.

[Fuxy]

I never understood the turning the lights on bit I found bright ambient environments hurt my eyes more when trying to concentrate looking at the screen then dark environments.

Then again most websites I use regularly have been re-skinned to have dark themes since white hurts my eyes regardless of the ambient environment.

[allegory]

Sounds like you need to see the optician. I had the same trouble and they sorted it :)