My guess is that being blinded (for creatures that can be meaningfully blinded) takes a big chunk out of all your skill rolls.
Sounds very probable. A viable way to test this could be to remove eyes and see if sparring accidents go up dramatically...although failed dodges/parrys/"soft" hits could be cancelled out by the dwarfs simply missing. I will test this tomorrow.
Does working in a workshop call for a skill roll?
Because then one could alternatively have a legendary Dwarf massproduce items and check if the masterwork quota (25% on lvl. 15 I believe?) is met.
hmmm...this of course would mean that your fortress wealth production is basically crippled while the dwarfs are blinded.
EDIT1:
Heavy Bleeding. Possible extreme pain depending on Toughness and number of eyes removed. Destroys accuracy and lessens vision permanently. If all eyes are removed, the creature is completely blind, and can only "see" what's next to it (other words, 3x3 vision).
This seems to imply blindness only affects accuracy, no mention of skill checks. Is mining an attack directed at the wall? The wiki could be wrong though...can anyone confirm?
EDIT2:
Did the massproduct test. I let a legendary Mason produce/r doors for 30 (realtime) minutes without eyes, then savescummed and did it again with eyes added back in.
Here's how he did:
| Masterwork | Exceptional | Superior | Fine | Well || Total
V1 | 0 | 0 | 5 | 7 | 2 || 14
V2 | 4 | 17 | 5 | 0 | 0 || 26
In percantage:
| Masterwork | Exceptional | Superior | Fine | Well || Total
Blind | 0 | 0 | 35% | 50% | 15% || 100%
Eyes | 15% | 65% | 20% | 0 | 0 || 100%
So it seems blind dwarfs have reduced skill rolls. The wiki tells us that blindness means reduced accuracy and I don't see a reason why combat checks should be different from other skill checks so I think I can skip the sparring check.
In conclusion: Removing the eyes does keep your miners from producing stone, but your forts wealth production is greatly reduced.
I can still see me using this method for larger digging projects.