I think it is maybe a leftover from the Olden Days, when the retinal reattachment surgery was not so easy.
I know of a woman who was informed about such a possibility, she had -15 vision and high blood pressure. She went on to have two kids without a c-section.
Here are some Wikipedia quotes.
"Retinal detachment is more common in people with severe myopia (above 5–6 diopters), in whom the retina is more thinly stretched. In such patients, lifetime risk rises to 1 in 20."
"...ophthalmologists generally advise patients with high degrees of myopia to try to avoid exposure to activities that have the potential for trauma, increase pressure on or within the eye itself, or include rapid acceleration and deceleration."
I think it made sense in the very old days - kind of a "compare the potential losses" thing, if it happens, hard to fix it. Permanent blindness is scary.
Google for "childbirth, pushing, blood vessels, eyes" and you'd get a million results. Just blood vessels, though, not retina.
Found this paper on PubMed:
"High myopia is not the indication for the cesarean section, but the patients should be examined after the delivery."
I knew a woman who was a retired eye surgeon. I wish I had asked her about these things.