Blindness categories and classifications
Blindness encompasses a wide variety of vision impairments, ranging in severity from partial to total blindness.
Legal blindness, or statutory blindness, is a specific definition of vision loss codified in certain legal systems. Under American law, a legally blind person is a person who has a best corrected visual acuity of 20/200 or worse in their better eye. This means that an individual must be ten times closer, or that an object must be ten times larger for it to be seen by an individual with 20/200 visual acuity, as compared to a person with 20/20 vision.
Legal blindness can also be determined by a field of vision restricted to 20 degrees or less in the best eye. Often called tunnel vision, a person with a 20 degree or less field of vision may have 20/20 acuity remaining, but their field of vision is severely restricted, thereby meeting the definition of legal blindness. People who are legally blind may be eligible for certain government benefits, including financial assistance and educational services.
Under American law, people with legal blindness also face certain restrictions, such as being prohibited from obtaining a driver's license, in most cases.
It is important to note that legal or statutory blindness is a specific definition used for legal and medical purposes and does not always accurately reflect a person’s ability to function in daily life. With appropriate accommodations and support, many people with legal blindness can fully participate in society.
Total blindness is classified as complete loss of vision, and is sometimes referred to as NLP, an acronym for “no light perception.” Only an estimated 15% of people with vision impairments have total blindness. Individuals who have total blindness have no perception of light, movement, or color. The causes for total blindness vary and include congenital diseases, incurred injuries, trauma, and other health conditions, such as glaucoma. Additionally, those who suffer from end-stage diabetic retinopathy may also experience total blindness.
People with total blindness may require substantial support and accommodations to independently function within their environments. These typically include the use of assistive technologies, tactile cues, and orientation and mobility training to travel safely.
Total blindness can pose significant challenges. However, despite considerable obstacles, with proper support and accommodations, people with total blindness are able to lead fulfilling lives.
Partial blindness is a more moderate form of blindness that reduces an individual's ability to see in either the central or peripheral vision. People with partial blindness may experience blurred vision, difficulty reading, difficulty recognizing faces, and trouble seeing in low light. The causes for partial blindness are varied, and include conditions such as glaucoma, diabetic retinopathy, macular degeneration, and, more commonly, cataracts.
People with partial blindness may experience challenges in daily life, such as performing certain everyday tasks like reading, using a computer, or driving, as well as properly navigating their environment inside and outside their home. Treatment for their condition (in the form of contact lenses, glasses, and/or laser surgery), along with vision rehabilitation services can help these individuals lead full, active lives even when their vision cannot be restored to 20/20.
Color blindness, also known as color vision deficiency, is a genetic condition that limits one’s ability (either partially or completely) to distinguish between certain colors. Those who have color blindness typically have normal vision in other aspects of the visual world that does not require color discrimination.
The most common color pairings people with color blindness have difficulty distinguishing between are red and green, along with yellow and blue.
Color blindness is more common among men than women, with an estimated 8% of men of Northern European descent having some form of color vision deficiency.
People with color blindness may face certain challenges in daily life, including when engaging with a website or app.
Congenital blindness is a severe form of vision loss that is present at birth and is a result of damage to one or both eyes, the visual cortex of the brain, and/or the optic nerve before a person is born.
In some cases, vision impairment can be caused by genetic mutations. In others, vision loss can be a result of environmental factors such as infection, drugs or toxins, or a lack of oxygen during birth.
People with congenital blindness face unique challenges that impact their day-to-day lives. However, with proper education, accommodations, and relevant training and tools, people with congenital blindness can still lead full and fulfilling lives.
Examples of relevant tools include, but aren’t limited to, auditory or tactile learning tools, and assistive technologies like screen magnifiers or screen readers (such as NVDA and JAWS). Both methods of accessing information using a computer are instrumental in allowing people with partial or complete blindness to properly access websites.
Night blindness is a condition where an individual has difficulty seeing in low light, such as in dimly lit environments or at night (hence the naming convention). Night blindness can be caused by inherited retinal diseases like Retinitis Pigmentosa. However, it can also be incurred due to complications with various health conditions such as cataracts and glaucoma.
People who have night blindness can find it difficult to perform certain tasks at night or in dimly lit environments, such as driving. Additionally, people with night blindness may also experience other symptoms within these environments, such as a general reduction in visual acuity, delayed dark adaptation, and decreased peripheral vision.
Treatment for night blindness will largely vary depending on its underlying cause. If the latter includes an existing health condition, this will typically be addressed first. Additional remedial approaches include vitamin A supplements, wearing corrective lenses, or using assistive technologies such as night vision devices.
Snow blindness is a temporary vision impairment caused by exposure to bright UV light. Such exposure can occur in snowy or high-altitude environments and results in one or both corneas’ surfaces experiencing cellular swelling.
People with snow blindness can experience vision loss, blurred vision, eye discomfort, and sensitivity to light. However, individuals with snow blindness can still see movement and shapes.
Those suffering from snow blindness typically should rest their eyes in a darkened room and use artificial tears to relieve discomfort.
When skiing or ascending to high altitudes, individuals can protect themselves from snow blindness by wearing proper eye protection, such as sunglasses or goggles with UV protection.