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Blindness (visual impairment): what is it, types, causes and treatment

Blindness (visual impairment): what is it, types, causes and treatment

November 5, 2022

Vision problems is one of the most common physical conditions among the general population , estimating that the vast majority of people suffer or will suffer some type of visual problem throughout their lives. However, a vision problem of this kind does not have to involve any degree of blindness.

There are certain criteria that to consider a difficulty in the vision as blindness or visual impairment . Throughout this article we will talk about what is blindness, the different types that exist and what are their associated symptoms, causes and treatment.

What is blindness or visual impairment?

Blindness, also known as visual impairment or loss of vision, is a physical condition that causes decreased ability to see in varying degrees and causes a number of difficulties that can not be fully compensated for by the use of glasses or contact lenses.


To be more exact, the term blindness is used to define that condition in which the loss of vision is complete or almost complete.

The loss of vision can appear suddenly or suddenly, or develop gradually over time. Further, The loss of vision can be complete or partial ; that is to say that it can affect both eyes or only one respectively. It may even be partial because it only affects certain parts of the visual field.

The range of causes that can cause the loss of vision is extremely varied and range from those that directly affect the eyes to those that involve the cerebral centers of visual processing.


Further, deterioration in vision usually becomes more common over the years , being the most common risk factors the appearance of physical affections such as glaucoma, diabetic retinopathy, macular degeneration related to age or cataracts.

According to data from the World Health Organization (WHO) it is estimated that 80% of the visual disability is preventable or curable with treatment, including those caused by cataracts, infections, glaucoma, uncorrected refractive errors, certain cases of blindness childish, etc.

In the rest of the cases, people with a significant or total degree of blindness can benefit from vision rehabilitation programs, changes in their environment and assistance devices.

Finally, in data for 2015, there were 246 million people with low vision in the world and 39 million people diagnosed with blindness. Most of these people are in developed countries and are over 50 years old, but this may be due to the lack of data in developing countries.


Types of visual impairment

There are different types of visual impairment depending on the degree of impairment to the ability to see. This significance can involve from a partial vision to a blindness or complete visual impairment. The World Health Organization (WHO) developed the following classification of the different types or degrees of visual impairment .

To measure the degree of disability takes into account the vision in the best eye, with the best lens correction possible. Taking this into account, the classification is as follows:

  • 20/30 to 20/60: loss of mild vision or near normal vision
  • 20/70 to 20/160: moderate visual impairment or low moderate vision
  • 20/200 to 20/400: severe visual impairment or severe low vision
  • 20/500 to 20/1000: almost total visual impairment or almost total blindness
  • Lack of light perception: total blindness

In addition, depending on the specific conditions of the vision, the visual disability can also be classified as follows:

  • Poor visual acuity and complete visual field
  • Moderate visual acuity and reduced field of vision
  • Moderate visual acuity and severe visual field loss

To better understand these terms, it should be noted that visual acuity consists of the resolution with which we see. That is, the ability to perceive and differentiate visual stimuli. While the field of vision is the observable extension in each moment.

Finally, Legal blindness or extremely poor visual acuity is considered as such when the person has a visual acuity of 20/200 , even after lens correction. There are a large number of people diagnosed with "legal" blindness who are able to distinguish shapes and shadows but who can not appreciate the details of these.

And night blindness?

A type of blindness very little known is the night blindness, also known as nyctalopia. This type of blindness is a condition that causes great difficulties or inability to see with relatively little light.

It can also be described as an inadequate adaptation of vision to darkness and can be a symptom of several eye diseases such as retinitis pigmentosa, retinal detachment, pathological myopia or a side effect to certain drugs such as phenothiazines, among many other causes.

Causes of visual disability

There are many common causes to the appearance of a visual disability and blindness. However, the incidence of these varies considerably between the two conditions. The main causes of visual impairment in any degree can be:

  • Genetic defects
  • waterfalls
  • Glaucoma
  • Eye injuries
  • Brain injuries (cortical blindness)
  • Eye infections
  • Poisoning or poisoning from methanol, formaldehyde or formic acid
  • Other causes such as amblyopia, corneal opacification, degenerative myopia, diabetic retinopathy, retinitis pigmentosa, etc.

Existing treatments

There are some treatment options that can help correct vision defects and minimize possible further degeneration. The choice of one of these treatments will depend on the following considerations:

  • Degree of visual impairment or blindness
  • Causes of visual deterioration
  • Age of the person and level of development
  • General health status
  • Existence of other conditions
  • Expectations of the patient

Among the possible treatments or aids for the management of both a visual disability and blindness are included:

  • Control of the underlying disease of the visual disability
  • Extension systems such as lenses, telescopes, prisms or mirror systems
  • Mobility aids such as canes, guide or guide dogs or systems based on geolocation
  • Reading aids such as Braille, optical recognition applications, audio-written books or reading devices that convert printed text into sounds or Braille
  • Technological systems such as screen readers or amplifiers and Braille keyboards

Bibliographic references:

  • Brian, G. & Taylor, H. (2001). Cataract Blindness - Challenges for the 21st Century. Bulletin of the World Health Organization, 79 (3): 249-256.
  • Lehman, S. S. (2012). Cortical visual impairment in children: identification, evaluation and diagnosis. Current Opinion in Ophthalmology, 23 (5): 384-387.

Beyond Blindness: Pioneering Treatments for Diabetic Retinopathy (November 2022).


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