yes, it is harmful to the eyes and could affect vision over time. Because black lights emit UV radiations that is known as blue light. These light rays could prevent the retinal cells from forming cytochrome oxidase. This chemical transports oxygen to the cells involved in vision. Without cytochrome oxidase and oxygen, the cells of the eye could die. The temporary effect of black light is causing conjunctivitis and photokeratitis, which are inflammation of the different parts of the eyes. The long-term effect of black light is damaging sensitive eyes from light exposure to cause limits vision finally.
Black light itself will do no harm to the eyes, except for you do some reading in dark environment. As for the reason, you can't see so clearly, so you will put the visual objects so closely to yourself that it will cause fatigue with the eyes. Therefore, such as seeing the mobile phone after lights out, is one of the important reasons which causes myopic.
Yes, black light can possible cause some eye damages. A black light is a light bulb with an inner coating that restricts the wavelengths. They are not visible for men and they can transmit UV rays. You know that UV rays is harmful to your eyes, do does the black light. Long time expose in such rays and light, it will contribute to cataracts.