Vision problems are one of the most common physical conditions among the general population , and it is estimated that the vast majority of people suffer or will suffer from some kind of visual problem throughout their lives. However, a vision problem of this type does not necessarily imply any degree of blindness.

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

What is blindness or visual impairment?

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

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

Vision loss may come on suddenly or suddenly, or it may develop gradually over time. In addition, vision loss can be complete or partial ; that is, 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 lead to vision loss is extremely varied, from those directly affecting the eyes to those involving the visual processing centers of the brain.

In addition, vision impairment tends to become more common over the years , the most common risk factors being the appearance of physical conditions such as glaucoma, diabetic retinopathy, age-related macular degeneration or cataracts.

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

In all other cases, people with significant or total blindness can benefit from vision rehabilitation programmes, environmental modifications and assistive devices.

Finally, in 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 a lack of data in developing countries.

Types of visual impairment

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

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

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

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

  • Poor visual acuity and full field of vision
  • 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 extent observable at any given 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 correction by lens. There are a large number of people diagnosed with “legal” blindness who are able to distinguish shapes and shadows but cannot appreciate the details of these.

What about night blindness?

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

It can also be described as an insufficient 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 of certain medications such as phenothiazines, among many other causes.

Causes of visual impairment

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

  • Genetic defects
  • Waterfalls
  • Glaucoma
  • Injuries to the eye
  • Brain injury (cortical blindness)
  • Eye infections
  • Poisoning or poisoning by 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. Choosing one of these treatments will depend on the following considerations:

  • Degree of visual impairment or blindness
  • Causes of visual impairment
  • Age of person and developmental level
  • General health status
  • Existence of other conditions
  • Patient Expectations

Possible treatments or aids for the management of both visual impairment and blindness include

  • Managing the disease underlying visual impairment
  • Magnification systems such as lenses, telescopes, prisms or mirror systems
  • Mobility aids such as canes, guide dogs, or geolocation-based systems
  • Reading aids such as Braille, optical recognition applications, audio books, or reading devices that convert printed text into sound 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.