A 1963 study from the Archives of Ophthalmology revealed that 24 blind test subjects could experience visual hallucinations while on LSD. The visual hallucinations were limited, however. Only those who had several years of sight before going blind were able to experience visual hallucinations.
Those who lost their sight younger than 2 years old were all unable to have them. This is most likely due to the fact that they were unable to have enough visual experience to create a fully functional visual system during brain development. The study showed that a normal retina wasn’t needed for visual hallucinations induced by LSD. It claimed that visual hallucinations were no different than those of subjects with sight.
The test subjects most commonly saw spots, lights, dots, and flickers. The length of time one was blind had nothing to do with their ability to have the visual hallucinations. Intelligence, visual memory, and visual imagery in speech didn’t have anything to do with their ability to hallucinate either.