I just spent an hour writing out a response to this and accidentally deleted it ahahaha. Okay, here we go again. I'm still new to this community and am working toward my degree, so more established Historians please critique me!

First of all, we must understand how the economy of the middle ages functioned. As a pre-industrial age, the medieval period was predominantly based upon agriculture. Now, of course, society would have other economic aspects, such as trade. But during this era, it was primarily agricultural. This meaning peasants would be working upon farms to provide a variety of goods for trade and to be given to landowners, being the local lords. Now, imagine blinding the majority of the workforce. That would certainly drastically cripple the economy. But, in war how viable is this?

When we think of the medieval army composition, it's typically nobility and the upper classes taking the more prestigious roles, such as command, cavalry, and the men-at-arms. With the peasantry filling out the blanks. Within his proclamation known as the Assize of Arms in 1181, King Henry II states that it is the "obligation of all freemen of England to possess and bear arms in the service of king and realm", indicating to us that a medieval army would certainly consist primarily of the peasantry, as they would have been the majority within any nation. However, army composition isn't my forte', so more established historians should weigh in on this, but from my understanding, the peasant levies would make up the roles that required the least amount of training. And, the big one that comes to mind is crossbowmen. Crossbows required very little training to master (as noted in this article) and thus could be utilised en masse. Byzantine princess Anna Komnene records that "they pierce through a shield, then cut through a heavy iron corselet and wing their way through and out at the other side.". Showing us just how brutally efficient these weapons were. Crossbows, Pike Formations, and Polearms becoming more prevalent meant armies started to consist of more untrained peasantry, which also meant army sizes would have grown. This topic is covered in depth by historians like Geoffery Parker, it's typically referred to as the military revolution.

Now we have an idea of what the economic foundations were, and an idea of the army composition of an army within the middle ages. So, do we believe blinding an army would cause major economic damage? Before the increased prevalence of easy to use weaponry? Not really, as the main economic agricultural base would not suffer too much damage, as armies would have had a higher ratio of nobility to the peasantry.

To answer the final part of your question, I believe the war you're thinking of is one specific battle. That battle is the Battle of kleidion 1014 CE. This was part of a war between the Byzantine Empire and the Bulgarian Empire. The Byzantines were led by Basil II, also commonly known as Basil The Bulgar Slayer, and by his flattering nickname, I'm sure you can deduce how this battle ended hahaha. Historian Paul Stephenson notes within his book Byzantium's Balkan Frontier (Page 62) that this epithet was given popularity as a result of Basil's actions after this battle. Upon routing the Bulgarian forces, Basil II had taken thousands of prisoners, the true numbers are unknown, with primary sources such as Byzantine General Kekaumenos claiming 14,000 were taken, prisoner. Modern historian Vasil Zlatariski claims this number to be exaggerated. For ease, I'll be using the primary source numbers. So, upon taking these 14,000 men prisoner, Basil II proceeded to group them into groups of 100. And then had 99/100 men in each group blinded, meaning 13,860 men were rendered completely blind. That final 140 were then blinded in one eye, so they could lead the remaining men home. This was recorded by contemporary Byzantine Historian John Skylitzes on page 458 of his work titled Histories. The methods which they would utilise in order to blind people would include hot pokers, yes, but also simply gouging out the eyes or even pouring a boiling substance over the eyes would be used to accomplish the job, as noted by historian Jennifer Lawler on page 106 of the Encyclopedia of the Byzantine Empire.

So, we have established when this occurred and to what scale. Now we must ask why? The most accepted reason as to why this occurred is that the mass blinding was conducted as retaliation for the death of Basil II's favoured general Boteneiates, and it was to decimate Bulgarian morale. This was discussed within Vasil Gyuzelev's Short history of Bulgaria. As an act of vengeance, it was supposedly quite effective, as historian Stephen Runciman explains in A History of the First Bulgarian Empire that Tsar Samuel of Bulgaria, upon seeing his blinded army, died of a heart attack. This, however, is information based upon primary evidence provided by Greek Historian John Skylitzes, so we should regard this with some caution. But some historians believe it could have been because blinding was typically the punishment for rebellion. Historian Michael Evans states that this is a punishment within his work The Death of Kings: Royal Deaths in Medieval England. However, he states it was usually done as a means of rendering the opposition of being unable to lead an army, thus I do not believe that it was utilised in this case as a means of punishment. So, to answer your questions of was it widespread, the answer is not really. Supposedly William The Conqueror practised blinding as a form of punishment, but the Anglo-Saxon Chronicles claims it was propaganda manifested in order to damage his reputation. It's also noted that blinding and castration was established as a punishment for thieves, introduced by Henry I of England, as noted by the aforementioned Michael Evans. There are also stories of famous general Belisarius being blinded as punishment by Emperor Justinian I. It is however regarded as false.

Now, I have not found any information linking the reason for this to economic damage. I do not believe to have been the goal either, I align with the common consensus of revenge and reducing enemy morale. This is because I believe that the economy wasn't a well-grasped concept within the middle ages, and for an agricultural society, this battle has taken place before the advent of the military revolution and thus increase in peasant soldiers, the impact would not have been too greatly felt.

I hope I answered your question well! I'm still technically a "Historian in training", so there may be a few issues and I would love a more established member of the community to critique and give me tips of how to improve! Having to retype all this may have made it worse than my original response, which is annoying, but I hope it's still of high enough quality for r/AskHistorians.

Edit: Formatting. I originally used the old []() hyperlinks and it didn't work lol

Edit 2: Ran it through Grammarly, I forgot to do it originally as deleted first response and had to retype it

Edit 3: Bibliography. I always forget this part.

Primary Sources:

John Skylitzes- Histories.

Henry II- Assize of Arms.

Anna Komnene- The Alexiad.

Secondary Sources:

Jennifer Lawler- Encyclopedia of the Byzantine Empire.

Michael Evans- The Death of Kings: Royal Deaths in Medieval England.

Stephen Runciman- A History of The First Bulgarian Empire.

Vasil Gyuzelev- Short History of Bulgaria.

Paul Stephenson- Byzantium's Balklan Frontier.

Geoffrey Parker- Military Revolution: Military Innovation and the Rise of the West, 1500–1800.

Britannica Article