Causes of blindness and visual impairment in population aged ≥50 years

Among people aged more than equal to 50 years, out of total blindness, 92.9% was avoidable and only 7.1% was unavoidable. Cataract was the principal cause for blindness accounting for 66.2% of all the blindness, followed by non-trachomatous corneal opacity (7.4%), cataract surgical complications (7.2%), posterior segment disorders (5.9%) and Glaucoma (5.5%).

Definition of various categories of visual impairment
Blindness

Presenting visual acuity < 3/60 in better eye

Severe Visual Impairment (SVI)

Presenting visual acuity < 6/60 – 3/60 in better eye

Moderate Visual Impairment (MVI)

Presenting visual acuity < 6/18 – 6/60 in better eye

Early Visual Impairment (EVI)

Presenting visual acuity < 6/12 – 6/18 in better eye

Moderate Severe Visual Impairment (MSVI)

Presenting visual acuity <6/18-3/60 in better eye

Visual Impairment

Presenting visual acuity < 6/18 in better eye

Functional Low Vision

A person with impairment of visual functioning even after treatment and/or standard refractive correction, and a visual acuity of less than 6/18 to light perception, or a visual field of less than 10 degree from the point of fixation.

Cataract Surgical Coverage (Person) indicates how many persons received cataract surgery (one or both eyes) among all who were bilaterally pinhole blind due to cataract.
The numerator includes persons with one operated and one pinhole blind eye and persons with bilateral (pseudo) aphakia. The denominator includes the numerator, plus persons bilaterally pinhole blind due to cataract. Besides this, the indicator can also be calculated separately for PinVA <6/60 and <6/18.

Cataract Surgical Coverage (Eye) measures the proportions of eyes pinhole blind due to cataract, which have been operated so far.
The numerator includes all (pseudo) aphakic eyes. The denominator includes the numerator, plus eyes pinhole blind due to cataract. Besides this, the indicator can also be calculated separately for PinVA <6/60 and <6/18.

Table : Causes of blindness & visual impairment in population aged ≥ 50 years

CausesBlindness (%)SVI (%)MVI (%)EVI (%)MSVI (%) VI (%)
Uncorrected refractive error0.11.518.870.615.813.4
Aphakia uncorrected1.71.40.80.60.91.0
Cataract untreated66.280.770.223.972.071.2
Cataract surgery complications7.28.35.22.95.75.9
Trachomatous Corneal Opacity0.80.10.00.00.10.2
Non-Trachomatous Corneal Opacity7.41.70.60.30.81.8
Phthisis2.80.10.00.00.00.4
Glaucoma5.50.80.70.30.81.4
Diabetic Retinopathy1.21.10.70.30.70.8
Age related macular degeneration0.70.70.80.30.80.8
Other posterior segment disorders5.93.42.00.72.22.8
Globe/ CNS abnormality0.50.20.20.10.20.3