Blindness: Types, Causes, Risk Factor and More

Blindness is the inability to see with one’s eyes. Partial blindness refers to various levels of vision impairment, while total blindness refers to complete vision loss. 

Blindness can be the result of an injury, an underlying disease or a congenital disability.

Treating eye diseases that lead to blindness can often prevent this outcome. Recognizing early symptoms of a developing eye problem is crucial to receiving treatment in an early enough stage to avoid any vision loss.

What Is Blindness?

Blindness is the inability to see, either partially or totally. Partial blindness is also sometimes referred to as vision impairment. Eye doctors diagnose it when:

• A person’s best-corrected eyesight (the highest visual acuity they can reach using glasses, medication, or surgery) falls below a certain threshold
• A person’s visual field (the area that can be seen when their eyes are fixed on a specific point) is significantly smaller than normal.

The World Health Organization categorizes visual impairment into three levels. They are:

• Moderate visual impairment: someone with a visual acuity of 20/70 to 20/160
• Severe visual impairment: someone with visual acuity of 20/200 to 20/400 or visual field of 20 degrees or less
• Profound visual impairment: someone with visual acuity of 20/500 to 20/1000 or visual field of 10 degrees or less

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Types of Blindness

Aside from total and partial blindness, there are three additional types of blindness: color blindness, night blindness and snow blindness. 

Color Blindness

Color blindness is the inability to distinguish different shades of colors or the inability to see some or all colors. Colorblind people cannot tell the difference between certain colors, especially green and red or blue and yellow. Some cannot see any color at all and view the world in only their shade of gray.

Night Blindness

Night blindness refers to difficulty of seeing at night or in poorly lit areas. Night blindness is not in itself a disorder but a symptom of retinal degradation. Many people with night blindness can see well during the day or in well-lit areas.

Snow Blindness

Snow blindness refers to a loss of vision because of intensive exposure to ultraviolet light. You can still see shapes and movements if you are snow blind, but your vision is permanently reduced. Wearing sunglasses while outdoors can prevent this condition. 

Causes of Blindness

Aside from acute traumas and injuries to the face and eyes, several eye conditions can lead to advanced blindness. Among them are:

• Age-related macular degeneration
• Cataracts
• Diabetic retinopathy
• Glaucoma

Age-Related Macular Degeneration

Age-related macular degeneration is an eye condition that causes damage to the sharp and central vision. AMD damages the macula, the retina’s central part, resulting in the inability to see clearly and difficulty performing common tasks like driving and reading.

Someone with AMD has one of two types: wet AMD or dry AMD.

Wet AMD

Wet AMD occurs when abnormal blood vessels grow behind the macula and retina and cause fluid blockages within the eye. This type of AMD progresses quickly and requires emergency treatment.

Dry AMD

Dry AMD describes the thinning of the macula that happens gradually as you grow older. Dry AMD advances more slowly than wet AMD, eye-care professionals cannot treat it with either medication or surgery. However, lifestyle and diet changes can slow progression of this type of AMD.

Cataracts

Cataracts affect your eye’s lens and leading to cloudy vision, and they are the leading cause of blindness and the main cause of vision loss. 

The condition can be congenital (existing from birth), or it can develop later in life because of a variety of factors. In an early stage, doctors treat it with prescription eyeglasses. Late-stage cataracts require surgery when they become advanced enough to cause blindness. 

Cataract surgery removes your eye’s natural lens and replaces it with an artificial one. This removes the cataracts that are present and prevents more from growing. 

Diabetic Retinopathy

Diabetic retinopathy is an eye condition common among people diagnosed with diabetes, and it affects both eyes. It occurs as a result of progressive damages to the retina’s blood vessels and the light-sensitive tissues found behind the eye.

The leading cause of blindness for Americans aged 20 and 74 years old, diabetic retinopathy progresses in four stages. 

• Stage 1: Mild non-proliferative retinopathy. Small areas of the blood vessels within your eyes start to swell. 
• Stage 2: Moderate non-proliferative retinopathy. The swelling blocks some blood vessels in the retina.
• Stage 3: Severe non-proliferative retinopathy. Even more blockages form, and parts of the retina become undernourished. The body prepares to grow new blood vessels in those areas.
• Stage 4: Proliferative retinopathy. New blood vessels begin to grow along the retina and inside the vitreous fluid. These new vessels are weak and often leak or break, potentially leading to severe vision loss or blindness. 

Glaucoma

Glaucoma refers to a collection of eye conditions that can destroy the eye’s optic nerve. There are two types of glaucoma: open-angle and closed-angle.

• Open-angle glaucoma is chronic and progresses slowly. You may fail to notice any effects on your visions until it has advanced significantly. 
• Closed-angle glaucoma can occur instantly and progress quickly. It can also be very painful.

Ophthalmologists can treat both types, and the earlier the treatment begins the more likely it is to prevent blindness.

Risk Factors

Some major risk factors for blindness include:

• Aging
• The existence of certain diseases like diabetes mellitus, cardiovascular disease and hypertension
• Premature birth
• The presence of some vision disorders like strabismus and amblyopia
• Family history of blindness, diabetes or other vision-related illnesses
• Poor nutrition
• Failure to wear protective glasses
• Poor prenatal care (e.g., maternal smoking)

Signs and Symptoms

If you have total blindness, you will not see anything regardless of lighting or location. If you have partial blindness, you may experience:

• Poor vision in low-light areas
• Cloudy vision
• Double vision
• Decrease in vision
• Inability to tell what shape objects are

Early Signs and Symptoms of Blindness

Blindness rarely happens suddenly. Some of the early signs and symptoms of this condition include:

• Excessive light sensitivity
• Eye pain
• Difficulty focusing
• Itchy eye.
• Red eyes
• Abnormal eye alignment
• Pupils changing color from black to white

These signs and symptoms are common to many different eye disorders, and not all of them lead to blindness. Do not panic if you have one or more of the symptoms listed above. Your eye doctor will tell you if there is cause for concern.

Treatment Advances for Blindness

There are many different treatments for eye conditions that cause blindness.

• Refractive errors can be treated using prescription eyeglasses or contact lenses.
• Glaucoma can be treated using medications that lower eye pressure.
• Wet form macular degeneration can be treated with injections and medications.
• Cataracts can be treated with cataract surgery.
• Corneal scarring or swelling can be treated with a corneal transplant.

The U.S. Food and Drug Administration (FDA) also recently approved a gene therapy drug that treats certain forms of inherited vision loss. 

Preventing Blindness

To help reduce your risk of blindness, you can:

• Control your blood sugar levels. Diabetes mellitus is a leading cause of blindness. Consult your doctor to help you manage your blood sugar, blood pressure and cholesterol levels. 
• Eat nutritious food. Research has shown that food items like salmon and tuna, rich in omega-3 fatty acids, are good for your eye health.
• Protect yourself from eye injuries. Putting on protective gear while working or playing sports helps prevent blindness due to injuries.
• Do not smoke. Research has shown that smoking can lead to blindness by increasing your risk of developing cataracts, optic nerve damage and age-related macular degeneration.
• Visit your eye doctor regularly. If you have any symptoms of early blindness, your eye doctor will notice them and deliver the appropriate treatment.

FAQs

What causes blindness?

The leading causes of blindness in the US are eye conditions like age-related macular degeneration, diabetic retinopathy, cataracts and glaucoma. 

Uncorrected refractive errors account for a majority of blindness cases in developing countries. Other potential causes include strabismus, amblyopia, poor nutrition, smoking and eye injuries.

What are the types of blindness?

There are four primary types of blindness: color blindness, light blindness, snow blindness and total blindness. The differences among them are:

• Color blindness is the inability to distinguish certain colors. 
• Night blindness is the inability to see in low light environments. 
• Snow blindness is the inability to see because of the effects of ultraviolet light. 
• Total blindness refers to complete loss of vision.

References

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4. Types of Color Blindness. (June 2019). National Eye Institute.

5. What is Night Blindness? (December 2020). Cleveland Clinic.

6. Effects of ultraviolet light on the eye: role of protective glasses. (December 1991). Environmental Health Perspectives.

7. Revision of visual impairment definitions in the International Statistical Classification of Diseases. (March 2006). BMC Medicine.

8. Diabetic Retinopathy. (May 2019). Handbook of Clinical Neurology.

9. Glaucoma and Eye Pressure. (September 2021). National Eye Institute.

10. Prevalence and risk factors for eye diseases, blindness, and low vision in Lhasa, Tibet. (April 2013). International Journal of Ophthalmology.

11. What Is Adult Strabismus? (November 2021). American Academy of Ophthalmology.

12. Amblyopia (Lazy Eye). (October 2020). Cleveland Clinic.

13. Ab externo implantation of the MicroShunt, a poly (styrene-block-isobutylene-block-styrene) surgical device for the treatment of primary open-angle glaucoma: a review. (November 2019). BioMed Central.

14. Cornea Transplant. (February 2018). Cleveland Clinic.

15. FDA approves novel gene therapy to treat patients with a rare form of inherited vision loss. (December 2018). The Federal Drug Administration Agency.

16. Prevention of blindness and priorities for the future. (July 2001). The World Health Organization Bulletin.

17. Tips to Prevent Vision Loss. (August 2021). Centers for Disease Control and Prevention.

18. Smoking and Eye Disease. (March 2022). American Academy of Ophthalmology.