Watching solar eclipse with unaided eyes can easily cause great discomfort even though your eyes will not feel when you are watching. One of the reason is that the change of the luminance of the light rays is too fast for the eyes to get adjusted, thus making blurry vision and so on. Besides, the retina will get thermal injury due to absorbing the visible light and infrared light, and the ultraviolet rays and blue light can cause photochemistry injury to the eyes, too. Therefore, you should wear eye protection such as a pair of polarized anti-ultraviolet sunglasses when you are watching the solar eclipse. Or you can put a piece of transparent glass on the fire until there is carbon black coming out on the glasses, then you can look through this glasses at the solar eclipse.
Yea, when a solar eclipse occurs, you watch it without taking any measure, chances are that your eyes are hurt to a great degree. People are prone to under a condition named solar retinopathy in the process of watching a solar eclipse directly with eyes, that is to say, the sun do harm to the retina. Because when the ultraviolet light with high energy strikes the retina, free radicals form. They damage the photoreceptors in the back of the eye form, which allow the eyes to perceive light. As a result, vision decreases or even blindness occurs. Therefore, if you long to watch a solar eclipse, you can take necessary precautions such as projection or wearing specialized sunglasses. Do not take chances on watching a solar eclipse directly anyway.