The World Health Organization (WHO) classifies impaired vision into five categories:

• Low vision 1 is a best corrected visual acuity of 20/70.
• Low vision 2 starts at 20/200.
• Blindness 3 is below 20/400.
• Blindness 4 is worse than 5/300
• Blindness 5 is no light perception at all.

A visual field between 5° and 10° (compared with a normal visual field of about 120°) goes into category 3; less than 5° into category 4, even if the tiny spot of central vision is perfect.

Pedagogically:

• Total Blindness: the student who cannot see at all and who should use his other senses in learning.
• Legal Blindness: the student whose vision acuity is 20/200 in the better eye and the vision field is 20º or less.
• Partially sighted: the student whose vision acuity is from 70/20 to 200/20 after rectification.
• Low vision: the student who has a problem or more in vision and whose vision could not be rectified by the glasses and might affect his daily life activities.

The degree of visual disability differs and so impairment ranges low vision to total blindness. Therefore, each child differs from the other in his/her visual, sensory and hearing ability. This requires each child to have his/her own evaluation. The teaching aids and exam methods depends on the basis of the individual evaluation of the child on the condition that the curriculum should not be different from his visually able peers.