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World Sight Day 2023: In India, avoidable blindness is a significant public health problem. At least 2.2 billion people worldwide have a vision impairment. At least one billion of these 2.2 billion people have a vision impairment that could have been prevented or is yet to be addressed. Based on the 2015 to 2019 nationally representative ‘Rapid Assessment of Avoidable Blindness’ (RAAB) survey conducted in India, a group of researchers conducted a study that was published in the journal PLoS One in 2022.
The survey was conducted across India among people aged 50 years and above using RAAB version 6 methodology, which means that the technique does not provide information on human and financial resources, which are important determinants of eye health planning. As part of the study, visual acuity of participants were recorded, followed by lens examination using a torchlight.
A measure of the ability of the eye to distinguish shapes and the details of objects at a given distance is known as visual acuity. Normal visual acuity is 20/20 vision measured at a distance of 20 feet. This means that one can clearly see at a distance of 20 feet.
The WHO, in 2003, proposed the use of presenting visual acuity to estimate visual impairment and blindness. The corrected visual acuity of those who wear spectacles in their daily life, and the uncorrected visual acuity of those who do not wear corrective spectacles is known as presenting visual acuity, according to the US National Institutes of Health (NIH).
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Prevalence of blindness in Indians aged 50 years and above
The study found that the prevalence of blindness in people aged 50 years and above in India was 1.99 per cent, and that of visual impairment was 26.88 per cent.
Blindness is a condition in which presenting visual acuity is less than 3/60 in the better eye (the eye with less disease or better vision), and visual impairment is a condition in which presenting visual acuity is less than 6/12 in the better eye.
Older age and illiteracy were found to be associated with blindness. Cataract, corneal opacity, cataract surgical complications, posterior segment disorders, and glaucoma are the major causes of blindness, the study said.
“As per the most recent survey data, almost 2% (1.99%) of individuals over the age of 50 years suffered from blindness,” Dr Sandeep Buttan, Technical Lead, Eye Health & Health System Strengthening, Sightsavers India, told ABP Live.
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Conditions responsible for blindness and visual impairment among Indians
Cataract is a condition in which the eye lens becomes cloudy, and corneal opacity is the condition in which the clear surface of the eye becomes scarred, resulting in vision loss and a milky appearance. Posterior segment disorders refer to diseases affecting the retina, choroid, and optic nerve. The dense network of blood vessels and pigmented stroma between the retina and the sclera is known as choroid. Glaucoma is a group of eye conditions that causes blindness and visual impairment by damaging the optic nerve.
Cataract, corneal opacity, cataract surgical complications, posterior segment disorders, and glaucoma are responsible for 66.2 per cent, 8.2 per cent, 7.2 per cent, 5.9 per cent, and 5.5 per cent respectively, of all the cases of blindness.
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Of all the cases of blindness, 92.9 per cent are due to avoidable causes, and of all the visual impairment causes, 97.4 per cent are due to avoidable causes.
“In India, with the predominant elderly population, cataract is the leading problem for defective vision. In young adults, metabolic disorders such as diabetic retinopathy and hypertensive retinopathy are quite common. In children, refractive error (glass correction) is the most common eye condition. The majority of these problems are either preventable or correctable. A recent survey reveals that over 25% of individuals aged 50 and above suffer from visual impairment. In this group, 1.99% experience blindness, with age and illiteracy significantly linked to this condition,” Dr Sriram Simakurthy, Consultant Vitreoretina and ROP, Sankara Eye Hospital, Hyderabad, told ABP Live.
A condition in diabetics, in which high blood sugar levels damage the blood vessels in the retina, is known as diabetic retinopathy. Hypersensitive retinopathy is a condition in which the microvasculature of the retina is damaged due to high blood pressure. Both diabetic and hypertensive retinopathies can lead to vision loss and blindness.
Most of the visual impairment cases in India were caused due to cataract and uncorrected refractive errors. Diabetic retinopathy, glaucoma and age-related macular degeneration are also responsible for some cases of visual impairment.
“Cataract and uncorrected refractive errors are responsible for the majority of visual impairment in India. Although other diseases like diabetic retinopathy, glaucoma and age-related macular degeneration are also emerging as significant challenges,” said Dr Buttan.
Age-related macular degeneration is an eye condition that blurs the central vision, and occurs when ageing damages the macula, or the part of the eye that controls sharp, straight-ahead vision.
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Are vision problems reversible?
Visual field defects, which are conditions in which any part of the complex vision pathway from the back of the eye to the brain’s visual processing centre or occipital lobe is damaged, as a result of which a part of the visual field disappears, are irreversible, according to the US National Institutes of Health. These defects cannot be reversed because the retina and optic nerve do not regenerate.
Strabismus or crossed eyes can be reversed if detected early in life.
Early diabetic macular oedema, cataracts, corneal blindness, and refractive error are generally reversible, according to a 2013 study published in the journal South African Family Practice.
Meanwhile, age-related macular degeneration, glaucoma, optic atrophy, and retinal degeneration usually cause permanent loss of vision.
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Optic atrophy is a condition in which the optic nerve shrinks due to the shrinkage of retinal ganglion cells, or neurons located near the inner surface of the retina, which propagate visual stimuli to the brain.
“Most eye diseases like cataract and refractive errors can be easily treated with either a simple surgery (for cataract) or a pair of glasses (URE). Other eye diseases can be prevented from progressing with interventions like strict diabetes control (for diabetic retinopathy) or the use of eye medicines (glaucoma),” said Dr Buttan.
Surgical techniques such as LASIK can be used to correct refractive errors. LASIK, which stands for laser-assisted in situ keratomileusis, is a refractive surgical procedure which uses a laser to treat and correct vision problems caused by refractive errors, and is intended to reduce a person’s dependency on glasses or contact lenses.
“Certain vision problems are reversible when detected on time. Various surgical procedures such as LASIK, ICL, PRK, SMILE, and RLE, are available to correct refractive errors and offer clear vision, eliminating the need for spectacles or contact lenses,” said Dr Simakurthy.
Implantable Collamer Lens (ICL) is an artificial lens made of plastic and a collagen called collamer that can be used to improve moderate-to-extreme nearsightedness or myopia in people with good eye health aged less than 50 years.
Photorefractive keratectomy (PRK) is a laser eye surgery that can improve vision by changing the shape of the cornea so that vision problems caused by refractive error are treated.
Small incision lenticule extraction (SMILE) is a refractive procedure used to treat astigmatism (irregularly shaped cornea) and nearsightedness using lasers.
Refractive lens exchange (RLE) is a surgical technique in which ultrasound is used to remove the natural eye lens and replace it with an intraocular lens, a tiny, artificial lens for the eye that replaces the eye’s natural lens.
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