Summary: Please give options to turn off screen shake and turn off display of flashy dye colours.
Yes - some vision impaired people do play video games. People with partial vision represent a significant market.
Vision impairment is a sliding scale. Different types of video games represent different levels of challenge to those with visual impairments, so those with the least vision favour the types of games which provide the least visual challenge.
2D games tend to be less of a visual challenge than 3D games. Within the 2D genre, those with a fixed frame of reference, such as where the entire field of play is visible at once, are easier than those where the frame of reference moves predictably, such as side scrollers. Whether 2D or 3D, the challenge is greatly increased if the frame of reference moves unpredictably, such as a game with screen shake effects.
As an example in Mabinogi, think of golems. Their footsteps create screen shake when they run. Their stomp attacks also create screen shake. I'm guessing even fully sighted players can lose track of some on-screen detail when the screen is shaking, but they re-acquire a clear image almost instantaneously when the screen shake stops. For some vision-impaired players, it can take significant time to re-acquire the image after the screen shake stops and figure out where moving players and monsters have moved to. Again, there's a sliding scale here, and some vision-impaired players cope better than others. If a golem is stomping repeatedly, when the screen shake stops, for some it can be a challenge to re-acquire the image before the next stomp shakes things up again. This is not fun.
So, if you want to make the game more accessible for vision-impaired players, given an option to turn off all screen shake effects. Many games give this option, because many game designers don't want to make their games inaccessible.
The other big gripe for vision-impaired players is flashy dyes.
There's the obvious issue that flashing colours are simply distracting. They tend to draw your gaze away from the bits you're trying to look at, and I think fully sighted players also hate them for this reason.
But for vision-impaired players they are troublesome for another reason. I mentioned above that 2D games tend to be easier than 3D games for vision impaired players. (2D games can make a relaxing change from decoding real life, which is harder since it happens in 3D.) In most 2D games most moving objects have a consistent appearance, but in 3D games other players and monsters can turn around, which changes their appearance. Also, in most 2D games moving objects don't often overlap other moving objects, but this happens frequently in 3D games. So, in a 3D game, when the appearance of another player changes, our brain needs to figure out if this is because maybe the player is turning to face us or whether it is because the player has moved partially behind another player or object. If they are turning, their apparent colour may gradually change while if they are moving behind something else the colour tends to stay the same but the size of the area with that colour reduces. If they are wearing a robe which has a colour that is constantly changing, it's going to be a lot harder to figure out what is going on.
So, if you want to make your game more accessible to vision-impaired players, provide an option to turn off display of flashing clothing colours.
Would any epileptics support this request, or is the "flashing lights cause seizures" thing a myth?