As per The Rights of Persons with Disabilities Act, 2016, "blindness" refers to a condition where a person has any of the following conditions, after best correction:
- total absence of sight; or
- visual acuity less than 3/60 (person can see at 3 metres what someone with standard vision could see from 60 metres away) or less than 10/200 (Snellen, in feet) in the better eye with best possible correction; or
- limitation of the field of vision subtending an angle of less than 10 degree.
Used in India
- Economic blindness: Vision 6/60 or inability of a person to count fingers from a distance of 6 meters or 20 feet (note however that Vision 6/60 is no longer considered legally blind in India after changes to the definition of blindness to bring it in line with WHO)
- Social blindness: Vision 3/60 or diminution of field of vision to 10°
- Manifest blindness: Vision 1/60 to just perception of lightAbsolute blindness: No perception of light
- Curable blindness: That stage of blindness where the damage is reversible by prompt management e.g. cataract
- Preventable blindness: The loss of blindness that could have been completely prevented by institution of effective preventive or prophylactic measures e.g. xerophthalmia, trachoma and glaucoma
- Avoidable blindness: The sum total of preventable or curable blindness is often referred to as avoidable blindness.
- Colorblindness is the inability to perceive differences in various shades of colors, particularly green and red, that others can distinguish
- Night blindness is a difficulty in seeing under situations of decreased illumination
- Snow blindness is loss of vision after exposure of the eyes to large amounts of ultraviolet light
Blindness can be caused due to numerous conditions.
The main causes of blindness in India are:
- Cataract: 62.60%
A cataract is a clouding of the lens in the eye which leads to a decrease in vision. Cataracts are most commonly due to aging but may also occur due to trauma or radiation exposure, be present from birth, or occur following eye surgery for other problems, or due to other reasons.
- Refractive errors: 19.70%
Refractive error, also known as refraction error, is a problem with focusing light accurately onto the retina due to the shape of the eye. The most common types of refractive error are near-sightedness, far-sightedness, astigmatism, and presbyopia. Refractive errors are most commonly due to genetics and environmental/lifestyle factors.
- Glaucoma: 05.80%
Glaucoma is a group of eye diseases which result in damage to the optic nerve and cause vision loss. Glaucoma is most commonly due to ethnicity, genetics, diabetes, use of steroids and any trauma to the eyes.
- Posterior segment disorder: 04.70%
Posterior segment eye disease/disorderepidemiologically is commonly defined as diseases of the retina, choroid and optic nerve and primarily includes (other than glaucoma already discussed above) age-related macular degeneration and diabetic retinopathy. Age-related macular degeneration is a medical condition which may result in blurred or no vision inthe center of the visual field, most commonly due to ageing but also due to genetics and smoking. Diabetic retinopathy, also known as diabetic eye disease, is a medical condition in which damage occurs to the retina due to diabetes mellitus.
Other commons causes include:
- Surgical Complication: 01.20%
- Corneal blindness: 0.90%
- Posterior capsular opacification: 0.90%
- Other: 04.19%
The treatment of blindness depends on the cause of blindness, including but not limited to the following:
- For cataract patients, cataract surgery would, in most cases, restore their sight.
- Visual impairment due to uncorrected refractive error can be addressed by doing a refraction and providing appropriate spectacles.
- Inflammatory and infectious causesof blindness can be treated with medication in the form of drops or pills.
- Blindness due to nutritional deficiency can be addressed by dietary change.
Statistics in India
The WHO has estimated nearly 8 million blind in India. For the same period, the estimates were 12 million blind using the old NPCB definition. The difference in terms of blindness in the two estimates is around 4 million people or 50% extra blind individuals, who correspond to the category of severe VI in the WHO definition, but were assessed as blind as per the old NPCB definition.
References for More Reading and Understanding/Source