Some students taught by special education degree holders can have visual or hearing impairments, or both. Being visually impaired means that someone has such poor vision that even when corrected, it can still negatively affect his or her educational performance. Students with visual impairments can have partial sight or low vision, or be fully blind. They cannot see well enough to learn without assistance or in general education classrooms. People with partial sight and low vision can have some sight, while people who are blind usually have little or no sight. Being hearing impaired means that someone cannot hear, with or without amplification, to the point that it negatively affects his or her educational performance. Like the visually impaired, the hearing impaired usually cannot hear well enough to learn without assistance or in general education classrooms. Being hearing impaired does not mean deaf, though the deaf are fully hearing impaired. There is also a third, related category: deaf-blind. Most people who are deaf-blind often have another disability as well because the condition is usually caused by rubella, meningitis, or genetic or chromosomal syndromes. Deaf-blind students are often in their own special education classes because they have severe communication, developmental, and educational needs due to their condition.