Piggybacking on the OP, how were vision issues regarded among people who joined (or tried to join) the military? Were they precluded from fighting, allowed or forced into a support role? (To narrow the timeline, say among Roman legionnares from the late republic/early imperial, vs a French Knight in the 1500's)
I'm assuming they weren't simply left to 'deal with it' if their vision impairment was noticeable enough as intentionally leaving a soldier with a major handicap could jeopardize more than only himself, but I could of course could be wrong in that assumption.
Specifically about blindness, in Asia, it was often a tough thing to live with.
As in other places, blindness was often associated with the unnatural, an ill omen or a sign of evil. In Asia in particular, Buddhist tendencies saw being born blind as a form of karmic retribution for probably evils committed in a past life that they were paying for now. This meant that blind people were often ostracized and otherwise isolated, society at large being unsympathetic with their plights.
In a heavily agrarian society that was primarily based around hard labor, blind people would have struggled to find a place. Families that could support a non-contributing member were very few in number. In a society where there were no government agencies or centralized care systems to help the disabled, disabilities like blindness could have spelled death for some.
But the blind people in China and Japan showed intense determination and fierce independence in the face of their hardships.
In China, there were a great many guilds for various professions, and there was most certainly a guild for the blind. This guild, like many other guilds in China, was self governing and a separate entity from the Imperial Court ie not a part of government. It existed and acted through it's own agency and largely run by blind people, for blind people. Reportedly, the governing body was 48 people, of which 47 were blind. The only person not blind was the scribe, who needed to be able to see to write and transcribe.
This guild would help the blind into apprenticeships, organize for negotiating power, members helping one another in times of need, charge membership fees and make business investments, etc. The general jobs they handled were, as one might assume, jobs that did not require sight for them to become proficient at it. This included performance, such as dance or music or story telling, simple textiles, trading, teaching, banking. Surprisingly, they were also known for offering religious services (which theoretically should have been at odds with the stereotype that they were cursed or suffering evil, as evidenced by their condition, but apparently this was no bar to service).
The guild would also self govern, punishing it's members for breaking guild rules or committing crimes. In case of one of their members coming under attack, they would come to their aid. In case of physical attack, there would be guild guardsmen (notably not blind; would be fascinating if they were blind). In cases of defamation or legal troubles, members would advise and otherwise use the reputation and influence of the guild to defend their members. Top ranking, senior members would be paid from guild coffers.
So the blind would have been surprisingly very well integrated into society despite there being no social safety net ordained by the government to assist the disabled, assuming the guild had a presence in the area. In areas without, blind people would have likely been given jobs that they could still do, as the vast majority of families would struggle to feed an extra mouth that does no work. The exception, of course, being nobles and the privileged.
Interestingly in Japan, they also had a blind organization called the Toudouza, very much like what they had in China. But this guild focused primarily on entertainment, specifically the recitation of the Heikemonogatari, or the Story of the Heike, a Japanese epic, which would be accompanied by the biwa, an instrument.
The guild was self regulating and had a strict internal organizational structure, with a rigid and clear cut hierarchy of who was senior to who and who was junior. These ranks denoted whether one was an apprentice, a journeyman, an accomplished performer, teacher, or master. It also included ranks for the higher ups who managed and ran the guild. And of course, the ranking system denoted whether one was allowed to perform the Heikemonogatari or not, the primary source of income for the members.
The Toudouza was founded sometime in the 1200s and grew largely in popularity because of their reputation as 'caretakers of the Heikemonogatari' as well as their skill with the biwa. It was said that after a performance by a master in the Toudouza, the only sound that breaks the room's silence are the sounds of tears.
During the Warring States Period, the influence and popularity of the Toudouza steadily decreased as Japan was plunged into a period of 200 years of constant warfare and factionalism. The upper classes were too preoccupied with politics and warfare to entertain the thought of being patrons to the arts while the lower classes were worried about conscription, famine, and struggling to make ends meet under the crush of war time taxes. In fact, during the Sengoku Period, the only art form that samurai accepted was Noh performance, eschewing all other forms of art or music.
But the Toudouza found a fervent patron in a unique man of the time who loved the sound of the biwa and a passion for the story of the Heike people, which others found outdated. His name was Tokugawa Ieyasu, the man who would eventually come out on top at the end of the Sengoku Period, successfully uniting Japan and establishing the Tokugawa Shogunate, heralds of the Edo Period.
It was during this Edo Period that the Toudouza actually obtained a great deal of support and influence from the Tokugawa Shogunate because a great fan of theirs now literally ruled everything. Tokugawa gave the Toudouza a huge plot of land and buildings to house their guildhouse as well as decreeing that the Toudouza had a monopoly on reciting the Heikemonogatari. He also decreed the Heikemonogatari as one of the official ceremonial performances of the court. As an analogy, this is basically tantamount to picking the song "Don't Stop Believing" and making it the national anthem, making it 'official'.
As one can imagine, the Toudouza, with the backing of the government, gained an impressive amount of influence and authority as well as money. This all meant that the Toudouza, starting from the humble beginnings as the self organized group for the blind into one of the major power players of the country. Not bad for people that would have probably been considered dead weight in the absence of the organization.
As a side note, the Toudouza only accepted men and started having fairly strict requirements to get in once they were 'raised' by the Tokugawa Shogunate. It was not nearly as inclusive as the guild in China.
There were other blind guilds, such as the one for women, known as Gozeza. These female Gozeza members were known for singing hauntingly beautiful songs that were often tragedies or had a bittersweet feeling to it.
Many blind people who had the willpower and determination to learn skills, more often than not, singing and/or playing an instrument but also including religious rituals, ceremonial dance, acupuncture and massage, would have joined a guild or would have been trained in it by an artisan in the absence of a guild.
To sum it up, the blind were far from helpless. Much like today, they would have probably had a job and would have taken care of themselves as much as possible. Those that were in a blind guild's turf would likely have at least tried to join. Unfortunately, because of prejudice and superstitions, they would have not likely enjoyed much understanding from those around them but they were not ostracized terribly either.
Hope this answers your question! Cheers!
You may also want to look at the discussion in this thread. Which addressed a similar question.