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Causes of Blindness & Partial Blindness

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Introduction

 The most common causes of visual impairment globally are:

  1. uncorrected refractive errors (43%)
  2. cataracts (33%)
  3. glaucoma (2%). 
  4. infections
  5. Injuries
  6. genetic defects
  7. Poisoning
  8. age related macular degeneration
  9. diabetic retinopathy
  10. corneal clouding
  11. childhood blindness
  12. stroke
  13. prematurity

Blindness can occur in combination with such conditions as:

  • intellectual disability
  • autism spectrum disorders
  • cerebral palsy
  • hearing impairments
  • epilepsy

1. Refractive errors

Refractive errors include near sighted, far sighted, presbyopia, and astigmatism. Cataracts are the most common cause of blindness.

Other disorders that may cause visual problems These cases are known as cortical visual impairment. Screening for vision problems in children may improve future vision and educational achievement. Screening adults may also be beneficial. Diagnosis is by an eye exam.

This includes cataracts, the infections river blindness and trachoma, glaucoma, diabetic retinopathy, uncorrected refractive errors, and some cases of childhood blindness. Many people with significant visual impairment benefit from vision rehabilitation, changes in their environmental, and assistive devices.

2. Cataracts

Cataracts is the congenital and pediatric pathology that describes the greying or opacity of the crystalline lens, which is most commonly caused by intrauterine infections, metabolic disorders, and genetically transmitted syndromes. Cataracts are the leading cause of child and adult blindness that doubles in prevalence with every ten years after the age of 40. Consequently, today cataracts are more common among adults than in children. That is, people face higher chances of developing cataracts as they age. Nonetheless, cataracts tend to have a greater financial and emotional toll upon children as they must undergo expensive diagnosis, long term rehabilitation, and visual assistance. Also, according to the Saudi Journal for Health Sciences, sometimes patients experience irreversible amblyopia after pediatric cataract surgery because the cataracts prevented the normal maturation of vision prior to operation. Despite the great progress in treatment, cataracts remain a global problem in both economically developed and developing countries. At present, with the variant outcomes as well as the unequal access to cataract surgery, the best way to reduce the risk of developing cataracts is to avoid smoking and extensive exposer to sun light (i.e. UV-B rays).

3. Glaucoma

Glaucoma is a congenital and pediatric eye disease characterized by increased pressure within the eye or intraocular pressure (IOP). Glaucoma causes visual field loss as well as severs the optic nerve. Early diagnosis and treatment of glaucoma in patients is imperative because glaucoma is triggered by non-specific levels of IOP. Also, another challenge in accurately diagnosing glaucoma is that the disease has four etiologies:

1. inflammatory ocular hypertension syndrome (IOHS)
2. severe uveitic angle closure
3. corticosteroid-induced
4. a heterogonous mechanism associated with structural change and chronic inflammation.

In addition, often pediatric glaucoma differs greatly in etiology and management from the glaucoma developed by adults. Currently, the best sign of pediatric glaucoma is an IOP of 21 mm Hg or greater present within a child. One of the most common causes of pediatric glaucoma is cataract removal surgery, which leads to an incidence rate of about 12.2% among infants and 58.7% among 10-year-olds.

4. Infections

Childhood blindness can be caused by conditions related to pregnancy, such as congenital rubella syndrome and retinopathy of prematurity. Leprosy and onchocerciasis each blind approximately 1 million individuals in the developing world.

The number of individuals blind from trachoma has decreased in the past 10 years from 6 million to 1.3 million, putting it in seventh place on the list of causes of blindness worldwide.

Central corneal ulceration is also a significant cause of monocular blindness worldwide. As a result, corneal scarring from all causes is now the fourth greatest cause of global blindness.

5. Injuries

Eye injuries, most often occurring in people under 30. Injuries and cataracts affect the eye itself, while abnormalities such as optic nerve hypoplasia affect the nerve bundle that sends signals from the eye to the back of the brain, which can lead to decreased visual acuity.

Cortical blindness results from injuries to the occipital lobe of the brain that prevent the brain from correctly receiving or interpreting signals from the optic nerve. Symptoms of cortical blindness vary greatly across individuals and may be more severe in periods of exhaustion or stress. It is common for people with cortical blindness to have poorer vision later in the day.

6. Genetic defects

People with albinism often have vision loss to the extent that many are legally blind, though few of them actually cannot see. Leber's congenital amaurosis can cause total blindness or severe sight loss from birth or early childhood.

Recent advances in mapping of the human genome have identified other genetic causes of low vision or blindness. One such example is Bardet-Biedl syndrome.

7. Poisoning

Rarely, blindness is caused by the intake of certain chemicals. A well-known example is methanol, which is only mildly toxic and minimally intoxicating, and breaks down into the substances formaldehyde and formic acid which in turn can cause blindness, an array of other health complications, and death. When competing with ethanol for metabolism, ethanol is metabolized first, and the onset of toxicity is delayed. Methanol is commonly found in methylated spirits, denatured ethyl alcohol, to avoid paying taxes on selling ethanol intended for human consumption. Methylated spirits are sometimes used by alcoholics as a desperate and cheap substitute for regular ethanol alcoholic beverages.

8. Age-related macular degeneration (AMD)

Age-related macular degeneration (AMD) is a disease that blurs the sharp, central vision you need for “straight-ahead” activities such as reading, sewing, and driving. AMD affects the macula, the part of the eye that allows you to see fine detail. AMD causes no pain.

In some people, AMD advances so slowly that vision loss does not occur for a long time. In others, the disease progresses faster and may lead to a loss of vision in one or both eyes. As AMD progresses, a blurred area near the center of vision is a common symptom. Over time, the blurred area may grow larger or you may develop blank spots in your central vision. Objects also may not appear to be as bright as they used to be.

AMD by itself does not lead to complete blindness, with no ability to see. However, the loss of central vision in AMD can interfere with simple everyday activities, such as the ability to see faces, drive, read, write, or do close work, such as cooking or fixing things around the house.

9. Diabetic retinopathy

Diabetic retinopathy is one of the manifestation microvascular complications of diabetes, which is characterized by blindness or reduced acuity. That is, diabetic retinopathy describes the retinal and vitreous hemorrhages or retinal capillary blockage caused by the increase of A1C, which a measurement of blood glucose or sugar level. A s A1C increases, people tend to be at greater risk of developing diabetic retinopathy than developing other microvascular complications associated with diabetes (e.g. chronic hyperglycemia, diabetic neuropathy, and diabetic nephropathy). Despite the fact that only 8% of adults 40 years and older experience vision-threatening diabetic retinopathy (e.g. nonproliferative diabetic retinopathy or NPDR and proliferative diabetic retinopathy or PDR), this eye diseased accounted for 17% of cases of blindness in 2002.

10. Corneal clouding

The cornea, which as the window of the eye is limited to the front of the eye, has to be completely evenly curved and fully clear, so that the light rays coming into the retina produce an accurate image. Congenital corneal clouding as well as corneal clouding which appears in early childhood can, due to a decrease of visual acuity, lead to an insufficient development of the visual apparatus, thereby presenting a reason for visual impairment. When corneal clouding appears in early childhood in only one eye, the other eye takes over all the tasks of learning to see and the affected eye stays behind in its development. If corneal clouding in small children is not treated adequately as well early enough, then as of the time a child starts school, the developmental lag is difficult or not at all possible to make up for. It is therefore exceedingly important to prevent the appearance of this so-called amblyopia (weaksightedness).

Corneal clouding can be congenital or can appear during the course of a separate illness. Further causes can be injuries, chemical burns, inflammations and infections. A very common form of corneal clouding, which seldom occurs in industrial nations and very often occurs in developing countries, is caused by a lack of vitamin A which is a consequence of prevalent malnutrition in these countries.

11. Childhood Blindness

 Xerophthalmia, often due to vitamin A deficiency, is estimated to affect 5 million children each year; 500,000 develop active corneal involvement, and half of these go blind.
Retinitis pigmentosa
Retinopathy of prematurity: The most common cause of blindness in infants worldwide. In its most severe form, ROP causes retinal detachment, with attendant visual loss. Treatment is aimed mainly at prevention, via laser or Avastin therapy.

12. Stroke

The type of vision loss after a stroke depends on which part of the brain was affected by the stroke. Vision loss is caused by damage of the blood vessels which supply the nerve pathway as it travels through the brain. Most strokes affect one side of the brain. ... When it does happen it can result in blindness.

13. Prematurity

Amblyopia is a category of vision loss or visual impairment that is caused by factors unrelated to refractive errors or coexisting ocular diseases. Amblyopia is the condition when a child's visual systems fail to mature normally because the child either suffers from a premature birth, measles, congenital nubella syndrome, vitamin A deficiency, or meningitis. If left untreated during childhood, amblyopia is currently incurable in adulthood because surgical treatment effectiveness changes as a child matures. Consequently, amblyopia is the world's leading cause of child monocular vision loss, which is the damage or loss of vision in one eye. In the best case scenario, which is very rare, properly treated amblyopia patients can regain 20/40 acuity.

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