I just watched this episode and there is an error in the description. Michelle's horse actually suffers a broken leg during a race. Nothing to do with blindness. Of course Michelle grows attached to the horse and wouldn't let the vet put it down.
By coincidence Andy Griffith and crew knows a NASA scientist who specializes in laser surgery and it turns out it is just a hairline fracture and the scientist explains to Andy in simple language it is just like "welding" using laser light.
Nothing to do with blindness at all. They welded the horse's broken leg together.
25 more characters to go! Repeat, they welded the broken leg back together.