Blindness is a state whereby there is no visual perception. Blindness can be caused by either internal or external factors. Internal factors include infection of the physiological or neurological system while external factors are like chemicals or eye injuries. Just like deafness, blindness can manifest at birth or later on in life. Medical tests are essential to determine the level of blindness. Blindness can also occur when there is a hearing impairment, and a combination of the two conditions leads to deaf-blindness.