Here’s a telescope site with multiple cites under its section on “Naked-eye Solar hazards.” Apparently blue light is the main hazard, not thermal damage.
http://mintaka.sdsu.edu/GF/vision/Galileo.html
Here’s one quote below. YEESH!
"Further evidence that even prolonged staring at the Sun does not usually produce blindness is given in the work:
M. O. M. Tso, F. G. La Piana
The human fovea after sungazing
Trans. Amer. Acad. Ophthalmol. Otolaryngol. 79, pp. OP-788 to OP-795 (1975)
"Tso and Piana asked three middle-aged people, each with an eye that was to be surgically removed to prevent the spread of malignant melanoma, to stare directly at the Sun for one hour, a day or two before the operation. To quote from their summary:
Two of the patients sungazed with an undilated pupil, and, 24 hours later, recovered their preexposure visual acuity with no detectable scotoma. One of the patients looked at the sun with a partially dilated pupil, and 24 hours later her visual acuity dropped from 20/20 to 20/25.
"But even in that eye, whose pupil was dilated to 4 mm, acuity was back to 20/20 after another day, though the scotoma remained.
"After surgery, the eyes were examined under the microscope. Although damage to the retinal pigment epithelium was seen in every case, the photoreceptors appeared perfectly normal. The ages of the patients were 49, 55, and 57 years.
