Curious if this was a documented issue in the last 100, 1000+ years. I was just thinking about the one coming up in August and how I need to tell my kids not to stare at it.
Yes, absolutely. In fact, documentation and follow up of such retinal scars is closely tied to the development of retinal photocoagulation (later LASER) therapy:
Plato describes the potential dangers of eye injury like this "[...] I decided that I must be careful not to suffer the misfortune which happens to people who look at the sun and watch it during an eclipse. For some of them ruin their eyes unless they look at its image in water" (Plat. Phaedo 99d).
Théophile Bonet, a 17th century Swiss Physician, is credited with providing the first accurate description of central vision loss through light damage to the macula (the area of highest photoreceptor density in the eye). In the late 19th century, Czerny and his coworkers showed that focussing sunlight into the eyes of rabbits causes scarring of the retina- those experiments were later duplicated in humans on eyes that were scheduled for surgical removal.
In the late 1940s, Gerhard Meyer-Schwickerath, a German ophthalmologist, noticed that retinal detachment did not progress when it reached such retinal scars. This gave him the idea to use artificial scarring of the retina to treat and prevent retinal detachment. After years of experminentation and fine tuning he developed the Heliostat- a solar photocoagulator (essentially a Galilean telescope, designed to focus sunlight on the back of the eye) that could only be operated when the sun was visible. Since this was -especially in northern Germany- a significant limitation, other souces of light were tested, and by the 1950s the first Xenon photocoagulators were manufactured and used to treat retinal holes and tears, intraocular tumors and diabetic eye disease. While this was a far step ahead of the Heliostat, Xenon photocoagulation burns were quite large and traumatic and it was not until the production of the first ruby LASERs in the 1960s that ophthalmic photocoagulation therapy could be refined further.
Further reading:
Goes FJ (Ed.) "The Eye in History"
Palanker DV et al. "Fifty Years of Ophthalmic Laser Therapy" ARCH OPHTHALMOL / VOL 129 (NO. 12), DEC 2011
As a follow up question, I know I've certainly looked at the sun directly many times, and as far as I can tell I can see just fine still. Why is looking at an eclipse more dangerous?