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

We explain the causes and subtypes of this severe disability.

Visual impairment is one of the most common physical conditions among the general population.It is estimated that the vast majority of people suffer or will suffer from some type of vision problem during their lifetime. However, a vision problem of this type does not necessarily imply any degree of blindness.

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

What is blindness or visual impairment?

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

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

Vision loss may appear suddenly or suddenly, or it may develop gradually over time. In addition, vision loss may be complete, vision loss may be complete or partial.that is to say that it can affect both eyes or only one eye 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, ranging from those directly affecting the eyes to those involving the brain's visual processing centers.

In addition, deterioration in vision tends to become more common as we age, with the most common risk factors being those that affect the eyes.The most common risk factors are physical conditions such as glaucoma, diabetic retinopathy, age-related macular degeneration and cataracts.

According to data from the World Health Organization (WHO), it is estimated that 80% of visual impairment is 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 programs, environmental modifications and assistive devices.

Finally, as of 2015, there were 246 million people worldwide with low vision 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 blindness or complete visual impairment. The World Health Organization (WHO) elaborated the following classification of the different types or degrees of visual impairment.

To measure the degree of disability, vision in the better 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-total visual impairment or near-total 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 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 is the resolution with which we see. That is, the ability to perceive and differentiate visual stimuli. While the field of vision is the observable extent at any given moment.

Finally, legal blindness or extremely poor visual acuity is considered as such when the person possesses a visual acuity of 20/200even after lens correction. 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 low light.

It can also be described as an insufficient adaptation of vision to darkness and can be a symptom of various 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 may be:

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

Existing treatments

There are a few 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 impairment
• Age of the person and developmental level
• General health status
• Existence of other conditions
• Expectations of the patient

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

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