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I am currently studying color blindness, and there is no medicine that can help it. Is it possible nonetheless for someone who is color blind to have their eyes restored to normal color vision by replacing the patient's eyes with donor eyes? Please explain any answer. Thanks!
No this is not currently possible as eye replacement surgery is not possible.
Colour blindness is either congenital genetic, such as your X linked forms, or due to a degenerative condition such as retinitis pigmentosa. It can also be acquired through retinal damage or brain injury such as stroke effecting specific areas of the visual cortex.
One of the major problems in restoring colour vision would be that the brain itself may not have the required structure to interpret the signals. The visual cortex is 'patterned' as we develop beginning inside the womb and continuing as a baby. During this process neurological connections in the visual cortex are stimulated so that we develop the necessary networks to interpret the signals from our eyes. If we lack the input of our eyes the brain conducts something called neural pruning where the unused neural connections are destroyed never to be regrown. Therefore if you lack visual stimulus for colour you prune these connections. If we were to somehow replace this colour stimulus later our brains would not be able to interpret it. In a somewhat similar circumstance to this it has been found with individuals who are born with congenital cataracts. If they have their cataracts fixed later in life having spent their childhood blind, despite being able to 'see' they cannot interpret the images they receive.
In individuals who loose there colour due to degenration of the retina, if we were able to repair the retina, through stem cell or transplant therapy then perhaps colour vision would return.
An individual who lost colour vision due to brain injury cannot have their colour vision returned as we cannot repair such injuries.
Most forms of color blindness are caused by defects in the eyes, not the brain. Usually the receptors in they eye that are supposed to be sensitive to one fraction of the visible spectrum don't work properly. So yes, replacing the whole eye (I don't know if that's possible now) would in theory fix those forms of color blindness, thought it's likely that the brain would be confused getting a new kind of signal that it had never received before.
How Color Blindness Works
Roses are red, violets are blue -- well, bluish. The sky is blue, too. Grass is green. These are things that most of us know for a fact and don't question. But what if you were colorblind? What would you see? Is life one long black-and-white movie?
In "The Wizard of Oz," Dorothy Gale steps out of her black-and-white Kansas farmhouse and into the color-saturated Land of Oz. She moves from a humdrum existence of chores and troubles to an intense fantasyland peopled with curious creatures, trading in a clapboard house for yellow brick roads, red ruby slippers and a brilliant green city of emeralds. What would her transformation have been without this rainbow of colors?
Color isn't just a component of vision. We associate color with beauty, like in a gorgeous sunset. Some colors have meaning in and of themselves -- purple is for royals, red signifies passion. Colors seep into our expressions -- If we're depressed, we say we're feeling blue. We're also "green with envy," we "see red" and we might go "white with fear." Colors even have practical meaning -- red means stop, green means go.
Certain colors are said to help you sleep, while others make you hungry. And never underestimate the effect of a bright red dress. Color is important.
To understand colorblindness, you need to understand some things about color vision.
The part of the eye that senses light and deals with color vision is called the retina. There are structures in the retina shaped like rods and cones -- rods help to see in low light, cones help to see in color and also with seeing details. Rods and cones contain photosensitive chemicals. In rods, this chemical is rhodopsin. The chemicals in cones are called photopigments. There are three kinds of cones, and each cone has a different photopigment that's sensitive to a certain wavelength of light. Because most of us have all three kinds of cones, normal human vision is called trichromatic.
Colorblindness is a misleading term. It makes everything sound black and white. Color vision deficiency might describe the condition more clearly. There are different kinds of color vision problems and different degrees of severity. Red-green color vision defects are the most common.
People who have mild color vision defects have anomalous trichromacy, which means that they do have all three types of cones, but one of the cones is defective. Someone with deuteranomaly, the least severe kind of colorblindness and also the most common, has unusual red cones, while someone with protanomaly has unusual green. People with deuteranomolous vision may not even know they don't see colors normally. Tritanomaly, trouble distinguishing blue and yellow, is quite rare.
People who are missing one type of cone altogether have dichromatic vision, which is more serious than anomalous trichromacy. Within this category of dichromatic vision, we have three different types.
- Deuteranopia: no green cones (also referred to as L cones, as in sensitivity to long wavelengths of light)
- Protanopia: no red cones (M or medium wavelength cones)
- Tritanopia: no blue cones (S or short wavelength cones)
Monochromacy is the next step on the color vision ladder. Monochromats see life in black, white and shades of gray. There are two types of monochromacy: rod monochromacy and cone monochromacy. People with rod monochromacy, also called achromatopsia, also have very poor vision and a high sensitivity to light. They also have nystagmus, which makes your eyeballs look kind of wobbly.
An early mention of colorblindness comes from John Dalton in the late 1700s. Dalton was colorblind, and he requested that his eyes be examined after his death. He assumed that perhaps his eyes were tinted blue and absorbed light wavelengths differently from other people [source: OMIM]. Sometimes deuteranopia is referred to as Daltonism.
How do you see through someone else's eyes? It's difficult to say how someone else sees color, because it's so subjective. How do I know that what I see as red is what you see as red? Is my red richer and bolder than yours? Or faded and dim compared to what you see? You may have argued with someone over whether a pair of pants is navy blue or black and never quite seen eye to eye.
When you refer to a rainbow of colors, you think ROYGBIV: red, orange, yellow, green, blue, indigo, violet. So what does someone who's colorblind see? Nothing that varied and exciting.
With this brightly colored image, we'll look at how deuteranopia and protanopia (both types of red-green colorblindness) as well as tritanopia affect how someone sees.
Image courtesy Henrik Sorenson/Stone/Getty Images
Deuteranopia: The reds are all gone. The woman's dress appears greenish-gray, and the purple has left her umbrella. The green from the umbrella looks rather grayish. Even her skin has lost its pinkish tone.
Protanopia: Looks a lot like deuteranopia, doesn't it? Except that the red dress has gone to a darker gray.
Tritanopia: The yellow in the image has turned to a light pink. There's no orange. The blue of the sky has changed and so have all the reds. What you're mostly seeing looks like shades of pink and blue. It's duller.
Anomalous trichromats have trouble telling green, yellow and red apart. They may see no difference at all between the purple object you're holding up and the blue one (since the purple involves red light.)
A monochromat sees black, white and gray, and what he sees is probably rather blurry.
On the pros side, people who have mild red-green color deficiency are said to be better at detecting camouflage. Same with dichromats -- they're more attuned to texture, instead of being fooled by the patterns of color [source: Gene Reviews].
Contrary to popular belief, dogs and cats don't see in shades of gray. They do see colors, just not all of the colors. Apes and some monkeys see like us. Raccoons are colorblind, and so are whales and seals, but manatees can tell blue from green. Birds see even better than we do.
Lots of animals also have ultraviolet vision -- from birds to bugs, fish to lizards. Interestingly, after an injury or an event like cataract surgery, some humans gain ultraviolet vision. When the lens of a person's eye has been removed, the condition is called aphakia. Some people think Monet had the condition after his cataract surgery -- he claimed that the colors he saw had completely changed and were in fact "quite terrifying" [source: Fortune]. (Bonus fact: The urine of many rodent species reflects ultraviolet light, which may be why rodents have retained UV vision, unlike other mammals [source: National Geographic].)
Testing for Color Blindness
The kind of colorblindness test you're probably most familiar with is Ishihara plates and pseudoisochromatic plates (PIP). Ishihara plates were developed by Dr. Shinobu Ishihara for the Japanese army. His original plates were hand-painted in watercolor and showed Japanese characters. Now, an Ishihara plate shows an assemblage of color dots with a number in the middle made with different colored dots. Ishihara plates can help diagnose red-green color vision defects. It isn't the perfect test, though -- sometimes the colors in one set don't quite match up with the plates in a different set, or maybe they look different in one kind of lighting than in another.
The Navy, Marines and Coast Guard use the Farnsworth Lantern test, aka FALANT, to diagnose colorblindness. The FAA uses it as a backup test if someone fails the PIP test. The FALANT involves colored signal lights that have to be identified from a distance. Two lights are shown at once, and the person being tested must identify the color (red, green, or white). The lights, however, are darkened with a filter to prevent people who are colorblind from being able to tell colors apart by their brightness. All dichromats and almost all anomalous trichromats fail [source: Gene Reviews].
The most accurate test for diagnosing different types of colorblindness is the anomaloscope. The person being tested has to match colors by controlling the brightness of a yellow light on part of their screen and a mixture of red and green light on the other side. He adjusts these elements until both sides of the screen appear to have the same color and brightness. People with normal vision match things very precisely, while people with color vision deficiencies match things imprecisely.
In the 1960s, weather radar maps depicted weather patterns in shades of gray. In the '80s, they switched to colors with different levels of intensity. But there were also built-in design features you could use to go along with the colors -- a colorblind person could set one color to blink, for example. In the '90s, they got rid of the other features and got even more colors. Now, there are 16 different levels of color that all have different intensities.
Not surprisingly, these upgrades resulted in a lot of vision testing. Some of these tests took a very pragmatic bent and involve work samples -- as in, what the person would actually be doing in his daily job, like reading flight progress strips, instead of just whether he can differentiate between certain colors on a screen [source: Milburn].
Causes of Color Blindness
Where does color blindness come from? How does it happen? Like so many things, it's mostly about your genes -- the luck of the draw.
It's true that many more men than women are colorblind. About 8 percent of Caucasian men have red-green color deficiency, compared to .5 percent of women. Colorblindness is less common in African and Asian populations. Achromatopsia, complete colorblindness, affects one in 40,000 people. On the Pingelap islands, however, where marriage to relatives is common, achromatopsia occurs in 5 to10 percent of the population. Tritan defects affect fewer than 1 in 10,000 people around the world.
Red-green color blindness is sex-linked recessive -- it's carried on the X chromosome. Men have an X and a Y chromosome, so if the X chromosome carries the gene mutation for colorblindness, he's going to be colorblind. Women have two X's, so they'd have to get two copies to make it happen.
Tritanopia isn't sex-linked -- it's an autosomal dominant disorder, but it can also be acquired. Most acquired colorblindness falls under tritanopia. Glaucoma, for instance, can cause blue-yellow colorblindness. Men and women get tritanopia in equal numbers. Complete colorblindness is autosomal recessive.
Some drugs, like digitalis and chloroquine, can even cause colorblindness. So can some industrial chemicals, as well as injuries to the eye.
Here are some diseases and conditions that can cause color vision defects:
- macular degeneration
- sickle cell anemia
- multiple sclerosis
Aging also has an effect on color vision. Colors seem to fade as we get older.
Unfortunately, there's no cure for colorblindness. There are some corrective lenses that on the market that claim to help with colors, but they can mess with depth perception and other aspects of visions. With any luck, the future will hold surgical options or perhaps gene therapy, but for now, coping mechanisms are the best bet.
What the Color Blind Can Do
Color pleases us aesthetically and serves as a visual clue, but do we really need it? It's a question worth thinking about.
When an architect thinks about designing a building, he or she ensures that it's accessible to people with wheelchairs and tries to make allowances for people's handicaps. Does anyone take the colorblind into account?
Perhaps since it's not a condition that's visible (only visual), people have a hard time understanding it. And after all, you can't explain how you see. How would you explain green to someone who's never seen it? You could try to do it with verbal descriptions or with music, but it wouldn't be the same.
There are daily frustrations for people who are colorblind. They may have a limited color palette in their wardrobes, to avoid showing up on a first date in a bright purple shirt and mismatched pants. For a kid, crayons without labels are pretty much useless. Most frustrating, perhaps, is listening to other people talk about beautiful, colorful things and not being able to see them.
Colorblindness can also be an obstacle to certain careers. If you've seen "Little Miss Sunshine" (spoiler alert if you haven't), a boy's dreams of becoming a pilot are abruptly dashed when he realizes he's colorblind. It's true -- you can't be a pilot if you're colorblind. There are too many signals to catch that rely on color to keep other people safe. You might also have trouble being an electrician (matching color-coded wires), and a woman at a salon might not want you coloring her hair. If you search the Internet for colorblindness and careers, you'll come up with a whole list of can'ts.
But let's take graphic design. You might immediately write that off as a career for the colorblind. But not so fast. First of all, a good Web site design won't rely just on colors to highlight important elements. The designer will use other elements to set off the things that are most important -- different fonts, contrast. Second, colors on the Internet correspond to hexadecimal values. Blue isn't written in code as "blue" -- instead, it's #0000FF. So someone who's colorblind could potentially keep in mind the color wheel and remember which numbers match with which colors.
Visual Acuity and Low Vision
Visual acuity is a number that indicates the sharpness or clarity of vision. A visual acuity measurement of 20/70 means that a person with 20/70 vision who is 20 feet from an eye chart sees what a person with unimpaired (or 20/20) vision can see from 70 feet away.
20/70 can best be understood by examining a standard eye testing chart that you may have used in your own doctor's office during an eye examination.
In the United States, the Snellen Eye Chart (pictured at left) is a test that ophthalmologists and optometrists use to measure a person's distance visual acuity. It contains rows of letters, numbers, or symbols printed in standardized graded sizes.
Your eye doctor will ask you to read or identify each line or row at a fixed distance (usually 20 feet), although a 10-foot testing distance is also used.
If you can read line 8 (D E F P O T E C) from 20 feet away while wearing your regular glasses or contact lenses, the doctor records your vision (or visual acuity) as 20/20 with best correction.
If the smallest print you can read is line 3 (T O Z) from 20 feet away while wearing your regular glasses or contact lenses, the doctor records your vision (or visual acuity) as 20/70 with best correction.
Please note: An actual Snellen Eye Chart is much larger than the one depicted here therefore, it's not recommended that you use this chart to test your own (or a friend's or family member's) visual acuity.
Color Blindness (Color Vision Deficiency– Daltonism)
Color Blindness is the decreased ability to see colors or differences in color and may make some educational activities more difficult. However, problems are generally minor, and most color-blind people adapt. People with total color blindness (Achromatopsia) may also be uncomfortable in bright environments and have decreased visual acuity. Color Blindness is typically an inherited genetic disorder most commonly X-linked recessive inheritance. This means that a woman who cares this gene has 50% possibility to transmit to his son and, if she has the illness, 100% possibility to transmit. In almost all cases people retain blueyellow discrimination, and most color-blind individuals are anomalous trichromats rather than complete dichromats (they often confuse red and green items).
Monochromacy as known as “total color blindness” (Rod or Cone Monochromacy). Dichromacy- Protanopia (absence of red retinal photoreceptors) difficulties distinguishing between blue and green colors and red and green colors. 1% of males are affected. Deuteranopia-affects hue discrimination in similar way to protanopia. 1% of males are affected. Tritanopia-only red and green pigments are present with a total absence of blue retinal receptors, rare situation. Anomalous trichromacy is a common type of inherited color vision deficiency. Protanomaly-mild color vision defect with altered spectral sensitivity of red retinal receptors. Hereditary sex-linked (1% of males). Deuteranomaly-altered green retinal receptors: Most common type affecting red-green hue discrimination in 5% European males. Hereditary sex-linked.
Tritanomaly-affects blue-green and yellow-red/pink hue discrimination. Some of the inherited diseases known to cause blindness are
a. Cone dystrophy
b. Cone-rod dystrophy
d. Blue cone monochromatism
e. Leber’s congenital amaurosis
f. Retinitis pigmentosa
Sometimes is difficult to diagnose specially when we have a mild color blindness. In serious type swe can find visual chromatic tests as Ishihara and Farnsworth 100 Hue. These tests can be done in pre-school students but is easier to evaluate in students with 10 years old and more. Most clinical tests are designed to be fast, simple, and effective at identifying broad categories of color blindness. Electroretinography-Evaluate the retinal function by capturing the electrical activity on light stimulation. There is no cure for color deficiencies. But they can use lenses increasing the contrast between colors enhancing the chromatic discrimination. Many mobile and computer apps have been developed to help color blind individual to view better. Color blindness may make it difficult or impossible for a person to engage in certain occupations. A Brazilian court ruled that people with color blindness are protected by Inter-American Convention on the Elimination of all Forms of Discrimination against Person with Disabilities.
Conclusion It is important to monitoring the child and observe her behavior when the same cannot answer correctly about colors. Also, important to do an ophthalmological control since pre-school ages. By age 5 children with normal color vision can identify all of groups of colors in a couple of seconds.
© 2020 Ana Cristina Selvi Daniel. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and build upon your work non-commercially.
The most common treatment at the moment for color blindness is the use of tinted contact lenses or glasses. The red-tint lenses can help people who are color blind better distinguish between certain colors. The ideal lens or type of lenses for you or your child can be determine during an examination.
In addition to corrective lenses, many people who are color blind learn to adapt to their condition. At an early age, letting teachers know that a child is color blind can be helpful educators can adapt lessons knowing that a child has issues seeing certain colors. When driving or buying produce, there are many other visual and sensory cues that can be considered apart from color alone.
Tech companies are also assisting people with color blindness. A number of apps and computer programs have been developed to help people who are color blind. These are great resources for people who are color blind when using mobile devices, tablets, laptops, or desktops.
Is Color Blindness Recessive or Dominant?
People who cannot tell the difference between colors which are evident to the rest people are assumed to have color blindness. For less sever deficiency, people usually don't know they have it until they confirm it through a lab test.
People often have different questions about color blindness, and among the most common questions is, "Is color blindness recessive or dominant?" Before this question, how much do you know about color blindness?
For inherited color blindness, the underlying cause is abnormal photo pigments. Located within the retina of your eye, the the color-detecting molecules are called cone cells. And people needseveral genes to make these photo pigments, and any defect in these genes lead to color blindness.
Is Color Blindness Recessive or Dominant?
Color blindness is basically a recessive condition linked to sex &ndash it is transmitted in the 23 pair of chromosomes, which are spaghetti-like strands packed with genetic info. A normal person will have 23 pair of chromosomes in all cells other than sex cells. Males will have one X chromosome and one Y chromosome in the 23 rd pair of chromosomes, whereas females will have two X chromosomes only.
Since color blindness transmits via X chromosomes, it is therefore called a recessive trait. Any recessive trait will need two recessive genes of an organism to manifest that characteristic.
What Causes Color Blindness?
Most problems related to color vision are hereditary in nature and are present at birth. Every normal person has 3 types of cone cells in the retina, and these cones can sense blue, green, or red light. You can only see colors if your cone cells could sense different amounts of 3 basic colors. Sometimes, you don't have any of these cones, or they don't function properly. It means, you may find it difficult to identify 1 of these 3 colors or mistake the 3 colors.
Your color vision problem is not always related to genetics, and other factors can also affect the way you perceive colors. The factors include injury to the eye, aging, side effects of some medicines, and eye problemssuch as macular degeneration, glaucoma, diabetic retinopathy, and cataracts.
Any chemical or physical damage to the eye may also lead to color blindness. It may also result from any damage to the optic nerve or part of the brain that deals with color information.
Can Color Blindness Be Treated?
Now you already have the answer to your question, "Is color blindness recessive or dominant?" You may have another question, "Is it possible to treat color vision problems?" In case, your color blindness involves genetics, you cannot do anything to fix the issue. You don't need a treatment though if you're suffering from the most common type of color blindness, called red-green color deficiency, because it doesn't interfere with your normal life. In fact, you may not even know you have this type of color blindness.
However, you can find a treatment option for some acquired color vision problems. And it will depend on the underlying cause of color blindness. For instance, you can have your cataract removed if it's affecting your color vision. Here are some possible options to handle color vision problems.
- Your doctor may recommend wearing colored contact lenses, so you could see differences between different colors. Unfortunately though, these lenses can distort objects.
- You may consider wearing glasses designed specifically to block glare because most people can notice some color difference when there is less brightness or glare.
- You can also learn how to use cues like location or brightness rather than colors to manage things better in your life.
Types of Color Blindness
Is color blindness recessive or dominant? You already know it, and now you will want to learn a bit more about types of color blindness to better understand the whole issue.Depending on the photo pigment defects in different kinds of cells, you can divide color blindness in three categories: red-green color blindness, blue-green color blindness, and a complete absence of color vision which is the rarest of all three types.
Red-Green Color Blindness
It is the most common types of hereditary color vision problem and refers to a situation where your red cone or green cone photo pigments don't work at all.
When the red cone photo pigment is abnormal, it's called protanomaly. You will find colors less bright with orange, red and yellow appearing greener. Potanomaly is an X-linked condition that can affect 1% of males.
The absence of working red cone cells in male refers to the condition called protanopia. In this X-linked disorder, red will appear as black and certain shades of yellow, orange, and green will all appear as yellow. Protanopia is an X-linked condition and can affect 1% of males.
When the green cone photo pigment isn't normal in males, this condition is called deuteranomaly in which green and yellow appear redder. This is the most common color blindness form that can affect 5% males.
The absence of any working green cone cells is referred to as deuteranopia in which reds will look more as brownish-yellow.
Blue-Yellow Color Blindness
It's also quite common but rare than red-green color blindness.
You will be a patient of tritanomaly if your blue cone cells aren't fully functional. In this extremely rare condition, blue will appear greener, and you will have a hard time differentiating between yellow and pink.
You're suffering from tritanopia if blue appears green and yellow looks more as violet. That's mainly because you don't have any blue cone cells. This autosomal recessive disorder affects both males and females.
Complete Color Blindness
You're a patient of complete color blindness if you cannot experience any color at all. There are two basic types of complete color blindness.
Color Blindness Treatment
Gene therapy has cured color blindness in monkeys, according to researchers at the University of Washington.
While these findings in animals look promising, gene therapy would not be considered for humans until treatments are proven to be safe.
Meanwhile, there is no cure for color blindness. But some coping strategies may help you function better in a color-oriented world.
Most people are able to adapt to color vision deficiencies without too much trouble. But some professions, such as graphic design and occupations that require handling various colors of electrical wiring, depend on accurate color perception.
If you become aware early in life that you are colorblind, you may want to choose a career that does not require accurate color perception.
Diagnosing color vision deficiency early also may prevent learning problems during school years, particularly because many learning materials rely heavily on color perception.
If your child has a color deficiency, be sure to speak with his or her teachers about it, so they can plan their lessons and presentations accordingly.
The Origins of Modern Color Science
126.96.36.199 George Palmer
One of these two men was George Palmer. Gordon Walls (1956) , in an engaging essay, described his fruitless search for the identity of this man. It was Walls’ essay that first prompted my own interest in the history of color theory. In fact, Palmer was a prosperous glass-seller and, like Lomonosov, a specialist in stained glass ( Mollon, 1985 , 1993 ). He was born in London in 1740 and died there in 1795. His business was based in St Martin's Lane, but for a time in the 1780s he was also selling colored glass in Paris. His father, Thomas, had supplied stained glass for Horace Walpole's gothick villa at Strawberry Hill and enjoys a walk-on part in Walpole's letters ( Cunningham, 1857 ).
George Palmer represents an intermediate stage in the understanding of trichromacy, for he was, like Lomonosov, both a physical and a physiological trichromatist. In a pamphlet published in 1777 and now extremely rare, he supposes that there are three physical kinds of light and three corresponding particles in the retina ( Palmer, 1777b ). In later references, he speaks of three kinds of ‘molecule’ or ‘membrane’. The uniform motion of the three types of particle produces a sensation of white ( Figure 1.7 ). His 1777 essay attracted little support in Britain. The only review of this proto-trichromatic theory was one line in the Monthly Review: ‘A visionary theory without colour of truth or probability.’ In the French-speaking world, however, his ideas were better received: A translation of the pamphlet ( Palmer, 1777a ) attracted an extravagant review in the Journal Encyclopédie.
Figure 1.7 . George Palmer's proposal that the retina contains three classes of receptor, in his Theory of Colours and Vision of 1777. Only four copies of this monograph are known to survive.
Once equipped with the idea of a specific receptor, Palmer ran with it. In 1781 in a German science magazine, his explanation of color blindness is discussed, although his name is there given mysteriously as ‘Giros von Gentilly’ while ‘Palmer’ is said to be a pseudonym ( Voigt, 1781 ). He is reported to say that color blindness arises if one or two of the three kinds of molecules are inactive or are constitutively active ( Mollon, 1997 ). In a later pamphlet published in Paris under his own name ( Palmer, 1786 ), Palmer suggests that complementary color aftereffects arise when the three kinds of fiber are differentially adapted – an explanation that has been dominant ever since. To explain the ‘flight of colors,’ the sequence of hues seen in the afterimage of a bright white light, Palmer proposes that the different fibers have different time constants of recovery. And to explain the Eigenlicht, the faint light that we see in total darkness, he invokes residual activity in the fibers.
Another modern concept introduced by George Palmer is that of artificial daylight. In 1784, the Genevan physicist Ami Argand introduced his improved oil-burning lamp ( Heyer, 1864 Schrøder, 1969 ). In its day, the Argand lamp revolutionized lighting. It is difficult for us today to appreciate how industry, commerce, entertainment, and domestic life were restricted by the illuminants available until the late eighteenth century. Argand increased the brilliance of the oil lamp by increasing the flow of air past the wick. He achieved this by two devices. First, he made the wick circular so that air could pass through its center, and second, he mounted above it a glass chimney. Unable, however, to secure suitable heat-resistant glass in France, he went to England in search of the flint glass that was an English specialty at the time. While he was gone, the lamp was pirated in Paris by an apothecary called Quinquet, who was so successful a publicist that his name became an eponym for the lamps. For a time, however, Quinquet had a partner, no other than George Palmer – and Palmer's contribution was clever: He substituted blue glass for Argand's clear glass, so turning the yellowish oil light into artificial daylight. Characteristically, this novel idea was set out in a pamphlet given away to customers ( Palmer, 1785 ). The selling line was that artisans in trades concerned with color could buy the Quinquet–Palmer lamp, work long into the night, and so outdo their competitors. Palmer even proposed a pocket version that would allow physicians correctly to judge the color of blood or urine during the hours of darkness. The concept of artificial daylight appears again in a monograph by G. Parrot (1791) .
George Palmer never took the final step of realizing that the physical variable is a continuous one. Living only streets away from him in 1780 was another tradesman, John Elliot, who postulated transducers sensitive to restricted regions of a continuous physical spectrum – but who never restricted the number of transducers to three ( Mollon, 1987 in press).
Blindness: Causes, Types & Treatment
Blindness is defined as the state of being sightless. A blind individual is unable to see. In a strict sense, the word "blindness" denotes the inability of a person to distinguish darkness from bright light in either eye. The terms blind and blindness have been modified in our society to include a wide range of visual impairment. Blindness is frequently used today to describe a severe visual decline in one or both eyes with the maintenance of some residual vision.
Vision impairment, or low vision, means that even with eyeglasses, contact lenses, medicine, or surgery, someone doesn't see well. Vision impairment can range from mild to severe. Worldwide, between 300 million-400 million people are visually impaired due to various causes. Of this group, approximately 50 million people are totally blind. Approximately 80% of blindness occurs in people over 50 years of age.
When is one considered legally blind?
Legal blindness is not a medical term. It is defined by lawmakers in nations or states in order to either limit allowable activities, such as driving, by individuals who are "legally blind" or to provide preferential governmental benefits to those people in the form of educational services or monetary assistance. Under the Aid to the Blind program in the Social Security Act passed in 1935, the United States Congress defined legal blindness as either central visual acuity of 20/200 or less in the better eye with corrective glasses or central visual acuity of more than 20/200 if there is a visual field defect in which the peripheral field is contracted to such an extent that the widest diameter of the visual field subtends an angular distance no greater than 20 degrees in the better eye. Blindness in one eye is never defined as legal blindness if the other eye is normal or near-normal.
It is estimated that more than 1 million people in the United States meet the legal definition of blindness.
What are the different types of blindness?
There are three main types of blindness.
- is the inability to perceive differences in various shades of colors, particularly green and red, that others can distinguish. It is most often inherited (genetic) and affects about 8% of males and under 1% of women. People who are color blind usually have normal vision otherwise and can function well visually. This is actually not true blindness.
- Night blindness is a difficulty in seeing under situations of decreased illumination. It can be genetic or acquired. The majority of people who have night vision difficulties function well under normal lighting conditions this is not a state of sightlessness.
- Snow blindness is a loss of vision after exposure of the eyes to large amounts of ultraviolet light. Snow blindness is usually temporary and is due to swelling of cells of the corneal surface. Even in the most severe cases of snow blindness, the individual is still able to see shapes and movement.
People often say, "I am 'blind as a bat' without my glasses." All bat species have eyes, and most have excellent vision at night but not in daylight. More importantly, the term blindness means the inability to see despite wearing glasses. Anyone who has access to glasses and sees well with the glasses cannot be termed blind.
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What causes blindness?
The many causes of blindness differ according to the socio-economic condition of the nation being studied. In developed nations, the leading causes of blindness include
In third-world nations where 90% of the world's visually impaired population lives, the principal causes are infections, cataracts, glaucoma, injury, and inability to obtain any glasses. In developed nations, the term blindness is not used to describe those people whose vision is correctable with glasses.
Infectious causes in underdeveloped areas of the world include
The most common infectious cause of blindness in developed nations is herpes simplex. Other causes of blindness include
- retinopathy of prematurity,
- blood vessel diseases involving the retina or optic nerve including
- , infectious diseases of the cornea or retina,
- ocular inflammatory disease, ,
- primary or secondary malignancies of the eye, congenital abnormalities, hereditary diseases of the eye, and
- chemical poisoning from toxic agents such as methanol.
- poor prenatal care,
- premature birth,
- advancing age,
- poor nutrition,
- failing to wear safety glasses when indicated, poor hygiene, smoking, a family history of blindness, the presence of various ocular diseases, and
- the existence of medical conditions including diabetes mellitus, hypertension, cerebrovascular disease, and cardiovascular disease.
- In third-world nations where many people have poor vision as a result of a refractive error, merely prescribing and giving glasses will alleviate the problem.
- Nutritional causes of blindness can be addressed by dietary changes.
- There are millions of people in the world who are blind from cataracts. In these patients, cataract surgery would, in most cases, restore their sight.
- Inflammatory and infectious causes of blindness can be treated with medication in the form of drops or pills.
- Corneal transplantation may help people whose vision is absent as a result of corneal scarring.
What are risk factors for blindness?
A principal risk factor for blindness is living in a third-world nation without ready access to modern medical care. Other risk factors include
What are signs and symptoms of blindness?
All people who are blind or have visual impairment have the common symptom of difficulty seeing. People with similar levels of visual loss may have very different responses to that symptom. If one is born blind, there is much less adjustment to a non-seeing world than there is for people who lose their vision late in life, where there may be limited ability to cope with that visual loss. Support systems available to individuals and their psychological makeup will also modify the symptom of lack of sight. People who lose their vision suddenly, rather than over a period of years, also can have more difficulty adjusting to their visual loss.
Associated symptoms, such a discomfort in the eyes, awareness of the eyes, foreign body sensation, and pain in the eyes or discharge from the eyes may be present or absent, depending on the underlying cause of the blindness.
A blind person may have no visible signs of any abnormalities when sitting in a chair and resting. However, when blindness is a result of infection of the cornea (the dome in front of the eye), the normally transparent cornea may become white or gray, making it difficult to view the colored part of the eye. In blindness from cataract, the normally black pupil may appear white. Depending on the degree of blindness, the affected individual will exhibit signs of visual loss when attempting to ambulate. Some blind people have learned to look directly at the person they are speaking with, so it is not obvious they are blind.
What specialists treat blindness?
Ophthalmology is the specialty of medicine that deals with diagnosis and medical and surgical treatment of eye disease. Therefore, ophthalmologists are the specialists who have the knowledge and tools to diagnose the cause of blindness and to provide treatment, if possible.
How do health care professionals diagnose blindness?
Blindness is diagnosed by testing each eye individually and by measuring the visual acuity and the visual field, or peripheral vision. People may have blindness in one (unilateral blindness) or both eyes (bilateral blindness). Historical information regarding the blindness can be helpful in diagnosing the cause of blindness. Poor vision that is sudden in onset differs in potential causes than blindness that is progressive or chronic. Temporary blindness differs in cause from permanent blindness. The cause of blindness is made by a thorough examination by an ophthalmologist.
What are treatments for blindness?
The treatment of visual impairment or blindness depends on the cause.
What is the prognosis for blindness?
The prognosis for blindness is dependent on its cause. In patients with blindness due to optic-nerve damage or a completed stroke, visual acuity can usually not be restored. Patients with long-standing retinal detachment in general cannot be improved with surgical repair of their detachment. Patients who have corneal scarring or cataract usually have a good prognosis if they are able to access surgical care of their condition.
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Is blindness preventable?
Blindness is preventable through a combination of education and access to good medical care. Most traumatic causes of blindness can be prevented through eye protection. Nutritional causes of blindness are preventable through proper diet. Most cases of blindness from glaucoma are preventable through early detection and appropriate treatment. Visual impairment and blindness caused by infectious diseases have been greatly reduced through international public-health measures.
The majority of blindness from diabetic retinopathy is preventable through careful control of blood-sugar levels, exercise, avoidance of obesity and smoking, and emphasis on eating foods that do not increase the sugar load (complex, rather than simple carbohydrates). There has been an increase in the number of people who are blind or visually impaired from conditions that are a result of living longer. As the world's population achieves greater longevity, there will also be more blindness from diseases such as macular degeneration. However, these diseases are so common that research and treatment are constantly evolving. Regular eye examinations may often uncover a potentially blinding illness that can then be treated before there is any visual loss.
There is ongoing research regarding gene therapy for certain patients with inheritable diseases such as Leber's congenital amaurosis (LCA) and retinitis pigmentosa. Improvements in diagnosis and prevention of retinopathy of prematurity, a potentially blinding illness seen in premature babies, have made it an avoidable cause of blindness today.
Patients who have untreatable blindness need tools and help to reorganize their habits and the way in which they perform their everyday tasks. Organizations, such as the Braille Institute, offer helpful resources and support for people with blindness and for their families. Visual aids, text-reading software, and Braille books are available, together with many simple and complex technologies to assist people with severely compromised vision in functioning more effectively. In the United States and most other developed nations, financial assistance through various agencies can pay for the training and support necessary to allow a blind person to function.
John Milton and Helen Keller are well known for their accomplishments in life despite being blind. There are countless other unnamed individuals with blindness, however, who, despite significant visual handicaps, have had full lives and enriched the lives of those who have interacted with them.
Signs of Head Trauma to a Baby
Ultimately, it is the little things that will probably tip you off, such as excessive tearing whether your baby is crying or not, or squinting as he attempts to focus on your face. His head may tilt to the left or right when he looks at a toy or mobile, indicating he sees better in one eye. He might turn his head away from light or close his eyes in sunlight.
You may see a spot in one eye every time you look at a picture of your baby. If anything seems off, have your pediatrician check the infant's eyesight.