We explain the causes and subtypes of this severe disability.
Vision problems are 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 visual problem throughout their lives. However, such a vision problem does not have to imply any degree of blindness.
There are certain criteria to consider a vision difficulty such 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 loss of vision, is a physical condition that causes a decrease in the ability to see to varying degrees and that causes a series of difficulties that cannot be fully compensated for by wearing 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.
Vision loss can come on suddenly or suddenly, or develop gradually over time. Also, 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 cause vision loss is extremely varied, ranging from those that directly affect the eyes to those that involve the brain’s visual processing centers.
In addition, deterioration in vision tends to become more common over the years, with 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 impairment is preventable or curable with treatment, including those caused by cataracts, infections, glaucoma, uncorrected refractive errors, certain cases of blindness. child, etc.
In all other cases, people with a significant or total degree of blindness can benefit from vision rehabilitation programs, modifications to their environment and assistive devices.
Finally, in data from 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 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 range from partial vision to complete blindness or 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, vision in the better eye is taken into account, with the best possible lens correction. Taking this into account, the classification is as follows:
- 20/30 to 20/60: mild vision loss or almost 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: almost total visual impairment or near total blindness
- Lack of perception of light: total blindness
Furthermore, depending on the specific conditions of vision, visual impairment can also be classified as follows:
- Poor visual acuity and full visual field
- Moderate visual acuity and narrow 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 view is the observable extent at all times.
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.
And 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 difficulties or inability to see in relatively low light.
It can also be described as insufficient vision adaptation 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 of any degree can be:
- Genetic defects
- Eye injuries
- Brain injuries (cortical blindness)
- Eye infections
- Methanol, formaldehyde, or formic acid poisoning or poisoning
- Other causes such as amblyopia, corneal opacification, degenerative myopia, diabetic retinopathy, retinitis pigmentosa, etc.
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 impairment
- Age of the person and level of development
- General health
- Existence of other conditions
- Patient expectations
Possible treatments or aids for managing both visual impairment and blindness include:
- Control of the disease underlying visual impairment
- Magnification systems such as lenses, telescopes, prisms or mirror systems
- Mobility aids such as canes, guide dogs or guide dogs or systems based on geolocation
- Reading aids such as Braille, optical recognition applications, audio-described books, or reading devices that convert printed text into sounds or Braille
- Technological systems such as screen readers or amplifiers and Braille keyboards
- Brian, G. & Taylor, H. (2001). Cataract Blindness – Challenges for the 21st Century. Bulletin of the World Health Organization, 79 (3): 249–256.
- Lehman, SS (2012). Cortical visual impairment in children: identification, evaluation and diagnosis. Current Opinion in Ophthalmology, 23 (5): 384–387.