Color blindness, which is sometimes called color deficiency, is a condition in which a person can’t see colors normally. In many cases, the patient can’t tell certain colors apart. Many such patients, for example, can’t distinguish between green and red.
The problem lies in the retina, which contains two kinds of cells for detecting light. Rods detect darkness and light and help a person see in limited light. Cones enable people to perceive colors, and there are three types. Cones enable people to see either red, green, or blue. They send signals to the brain that then determines what colors the person sees.
A patient who is color-blind may have cones that are not working properly. For example, they may be detecting a different color than normal. The color-blind patient may also be missing some cones. In the most severe cases, they may have no cones at all and see everything in shades of gray. Fortunately, this type of color blindness is rare. At the other end, people with mild color blindness can perceive colors more or less normally in well-lit areas but have trouble in dim light.
Color blindness generally affects both eyes, and it typically does not get worse or better. Most people are born color-blind, but there are conditions that can cause a patient to become color-blind. As some of these conditions are serious, anybody who notices a decline in their ability to see color should talk to their ophthalmologist.
1. Macular Degeneration
Macular degeneration, which is sometimes called age-related macular degeneration (AMD) is the most common cause of vision loss in Americans over 40. The older somebody gets, the greater the chances of their developing the condition. While one in 14 people over 40 have the disease, one in three people over 80 have it.
The disease affects a part of the retina called the macula. One of the macula’s functions is to enable someone to see fine details. A person with healthy maculas can read, drive, or use a computer easily. Such tasks become increasingly difficult for a person with degenerating maculas.
Macular degeneration also causes color blindness. The macula contains more cones than any other part of the eye, so damage to the macula affects those cones. As the disease progresses, the patient loses more and more of their color vision.
By contrast, there are few or no rods in the macula, so they aren’t damaged. In fact, a patient with macular degeneration can have better night vision than somebody with normal eyes.
There are two types of macular degeneration: dry and wet. The dry form is far more common and affects around 80 percent of patients. As the patient ages, yellow protein deposits called drusen form under the retina. At the same time, the macula becomes thinner. Over time, the patient’s central vision deteriorates, while their peripheral vision remains normal.
In the wet type, new and abnormal blood vessels grow under the retina. They sometimes leak blood or other fluids and can thus scar the macula. Wet macular degeneration develops more quickly than the dry form and is thus considered more serious.
2. Cataracts
Cataracts are the chief cause of blindness in the world. Globally, there are more cases of cataracts throughout the world than glaucoma, diabetic retinopathy, and macular degeneration combined. In a cataract, the lens, which sits behind the pupil and the iris, becomes cloudy.
Cataracts are categorized by the part of the lens where they first develop. For example, a cataract that develops in the nucleus or central part of the lens is called a “nuclear cataract.” This type of cataract is most common in older people.
Cataracts gradually cause vision to become cloudy and blurry. Similarly, colors become less vibrant and harder to distinguish. They may also take on a yellowish tinge.
3. Glaucoma
Glaucoma is actually a group of eye diseases that damage the optic nerve. In most cases, glaucoma is associated with abnormally high pressure within the eye. It is an insidious condition that often causes no symptoms until the disease is quite advanced. In glaucoma, the peripheral vision deteriorates first.
Glaucoma is typically caused by a blockage of the drainage angle that allows excess fluid to drain out of the eye. Glaucoma can be chronic or acute, and the chronic type is the more common. The acute form is so sudden that it’s sometimes described as an attack. It includes symptoms like headache, eye pain, vomiting, and vision loss.
4. Diabetic Retinopathy
Diabetic retinopathy is an eye disease that can affect people with diabetes. The abnormally high blood sugar levels in a diabetic patient damage the retina’s blood vessels.
Diabetic retinopathy has two stages: non-proliferative diabetic retinopathy (NPDR) and proliferative diabetic retinopathy (PDR). NPDR is the early stage of the disease, and it is characterized by swelling of the retina caused by leaks from the blood vessels. Sometimes, the macula absorbs the fluids and consequently swells up. The resulting condition, macular edema, is the most common cause of vision loss in people with diabetes. In macular ischemia, blood vessels close off and thus prevent blood and other nutrients from reaching the macula.
In PDR, the retina starts growing new blood vessels that can bleed into the vitreous and cause the patient to see dark floaters. The new blood vessels can also cause the formation of scar tissue that can cause a detached retina or damage the macula.
5. Injury To The Eye
Injuries to the head and eye can also cause color blindness. Any injury that affects normal vision will also likely affect color vision. Some head injuries can cause brain damage that impair the brain’s ability to process information regarding color. Eye injuries that damage the optic nerve and/or retina can cause color blindness. UV rays, which are among chief causes of blindness in the world, can also cause color blindness. Exposure to certain chemicals, like some fertilizers or carbon disulfide, can cause color blindness. Eye injuries can also increase a patient’s susceptibility to disorders like cataracts that cause color blindness and vision loss.
6. Aging
People can lose color vision as they get older. As someone ages, their cones simply become less sensitive, so colors seem duller and become harder to distinguish. The various shades of blue are particularly likely to seem less vibrant than before.
Cataracts are a common cause of color blindness in older people. After the age of 40, proteins in the lens start to break down and very gradually cause the lens to become cloudy. Consequently, people over 60 years old may start showing signs of cataracts.
The various eye disorders described earlier are generally more common in older patients. As mentioned earlier, macular degeneration affects one out three patients who are over 80. Glaucoma and diabetic retinopathy are more common in patients over 40.
