… I’m over here, Dad.
Why is masturbation said to cause blindness? I realize the notion predates the invention of evidence, so I can understand why the belief persists. And I recognized the perceived value in threatening adverse consequences for taking matters into ones own hands. But why blindness specifically?
You’ll shoot your eye out.
Its true. When I had to get glasses, I stopped. Well, not stopped completely.
Actually, harming vision was one of a huge number of medical conditions it was supposed to bring about, with warnings dating back to the early 1700s.
This is a WAG, but many people experience the start of myopia with the onset of puberty. With the onset of puberty comes sexual experimentation, especially masturbation. While the two aren’t actually correlated, you can see how people might correlate them, especially in earlier centuries. Add in some 17th-18th century puritanism, and it’s a perfect mismatch for discouragement of a normal activity.
It’s all that squinting!
It wasn’t specific to blindness. There was also the threat of growing hair on the palms of one’s hands, or that it would cause one to go insane. It was all borne out of the need to scare kids out of doing anything remotely enjoyable because enjoying life is a sin.
I Think I’m Turning Japanese.
Someone told me once that it “was obvious” that that phrase referred to the scrunched up face some make during masturbation orgasm. I never bothered to listen to the song.
Hershele Ostropoler, you are assuming that the people promulgating the belief in fact believed it, which is not a safe assumption. Look at Santa Claus: taught to children by adults who don’t believe. I don’t know one way or the other, but it’s worth investigating whether people believed it or merely said they did in order to coerce children into avoiding “sinful” behaviour.
ETA: As to why blindness, I suppose one possible reason is because you’d need to have something with a gradual onset. Easier to sustain belief, or at least avoid outright skepticism.
I wish I could answer the OP, but I can’t quite make out the text. Now if you will excuse me, I must go shave my palms…AGAIN! 
I am sure there are zillions of psychoanalytic essays stemming from Freud on this.
I’m pretty sure the hair on the palm thing isn’t to scare kids 
I suspect it’s more related to the “sinful” aspect of masturbation rather than any medical consequence. “Striking one blind” is one of those “godly” punishments
A quick Google search yielded lots of web pages that claim the “blindness” threat dates back to Franciscan monks in the 1700s… but I have been unable to find a verifiable source for this (the pages I saw were Q&A type pages without sourced references).
The following is pure conjecture…
I wonder if there might be some microscopic basis in reality here… poor sanitation leading to eye infections perhaps?
By the 1970’s, this was laughable.
But we did know that masturbation caused acne
Sexual intercourse, however, cleared up acne.
What was the difference? Perhaps the co-mingling of both sexes’ secretions
So then shouldn’t all the gay people have acne?
Answer: if you asked that, it meant you were gay.
Devo’s “Uncontrollable Urge”?
In his novel Dracula, Bram Stoker explicitly states that the Count has hair growing on his palms. It might have been meant as an eeerie detail to make him seem weird, or it may, as some claim, be an invocation of the observations of Cesare Lombroso (loading on Dracula the characteristics of an atavistic “criminal type”), but in the modern world, it’s hard to avoid thinking that the Count had his own way of whiling aweay the dull hours of daylight in his coffin.
What Devo song isn’t about masturbation?
Not only blindness and hairy palms.
From Wikipedia: History of Masturbation
Dr. Balthazar Bekker in 1716, said it caused , “disturbances of the stomach and digestion, loss of appetite or ravenous hunger, vomiting, nausea, weakening of the organs of breathing, coughing, hoarseness, paralysis, weakening of the organ of generation to the point of impotence, lack of libido, back pain, disorders of the eye and ear, total diminution of bodily powers, paleness, thinness, pimples on the face, decline of intellectual powers, loss of memory, attacks of rage, madness, idiocy, epilepsy, fever and finally suicide.”
The insanity thing, I’ve read there is a correlation, though I suspect it had more to do with the fact that at the time, treatment of the insane consisted of locking them up and, well, that was it, and they were bored. Hairy palms I can at least see a connection to the act in question.