You can be blind by level 3 with a little bad luck.

If you do the math a bit, as one of my DMs did, you realize that by level 11 everyone in the party will be wearing an eyepatch and be short of an eye, at the least, and will likely have multiple other performance inhibiting effects. There are 9 choices, determined by a d20 roll. All that the basic critical hit does in this edition is increase damage (HP reduction) done on that attack. Why? Because the PC's receive many attack rolls against them eventually everyone ends up with a lingering injury. I've had two DMs use this rule, and each of them chose after a time to get rid of 'receives a critical hit' triggering criteria. Fails a death saving throw by 5 or more.

Drops to 0 HP but is not killed out right.For DMs who don't like there being few consequences for dropping to 0 HP, in the DMG on page 272 there is an optional rule for lingering injuries that covers any PC who: There are no rules in the PHB limiting how often a PC can get up after being knocked to 0 HP.

System shock table 5e