What is Color-Blindness

Color-blindness is the inability to distinguish the differences between certain colors. This condition results from an absence of color-sensitive pigment in the cone cells of the retina, the nerve layer at the back of the eye.
Most color vision problems are inherited and are present at birth. Approximately 1 out of 12 males and 1 out of 20 women are color blind.

What does a color-blind person see?

A person with color-blindness has trouble seeing red, green, blue, or mixtures of these colors. The most common type is red-green color-blindness, where red and green are seen as the same color.

Here are some illustrations of the most common forms of color-blindness:

The colors of the rainbow Normal color vision	The colors of the rainbow Deuteranope (simulation) Absence of green retinal photoreceptors
The colors of the rainbow Protanope (simulation) Absence of red retinal photoreceptors.	The colors of the rainbow Tritanope (simulation) Absence of blue retinal receptors

Tests for Color-Blindness

The typical test for color-blindness is based on a person's ability to see numbers inside a circle.
Before you look at these tests, be aware of the following:

1. Your computer and monitor may not display the colors accurately. If you cannot see the number that does not necessarily mean you are color-blind. The numbers may more visible with some resolutions and display settings than with others.

2. The results of this test are not to be considered a valid medical test for color blindness and merely serve to illustrate the tests available. If you have any questions about your own possible color vision deficiencies consult a licensed medical professional.

Here is a sample of charts used to test for color-blindness.
There is a number in the center of the circle.
If you can see the number, chances are you are not color-blind.

Plate 1 What number do you see?	Plate 2 What number do you see?
Plate 3 What number do you see?	Plate 4 What number do you see?

Here are the answers: Plate 1 Those with normal color vision should read the number 74. Plate 2 Those with normal color vision should read the number 6. Plate 3 Those with normal color vision should read the number 29. Those with red-green deficiencies read the number 70. Those with total color-blindness can not read any number. Plate 4 Those with normal color vision should not be able to read any number. Most of those with red-green deficiencies should read the number 5. Those with total color -blindness can not read any number.

Can Sunlight Damage a Toddler's Eyes? by Kay Ireland, Demand Media

You slather your toddler's sensitive skin in sunscreen to protect her from the sun's rays, but your toddler's eyes can be just as sensitive to the sun and there's no lotion that can help. By understanding the ways the sun can damage your toddler's eyes, you can choose protection to keep his eyes safe and healthy.

Short-term Risks

Children are especially at risk for sun damage to the eyes because they typically spend more time in the sun, according to the American Optometric Association. The sun emits UV rays, which are a type of radiation. When exposed to high amounts of UV rays, a toddler can experience photokeratitis, which is essentially a sunburn of the eye. The condition is short-lived and causes mild pain and discomfort, such as a gritty and burning sensation in the eyes.

Long-term Issues

While photokeratitis doesn't have any lasting effects on your toddler's eye, excessive and frequent exposure to UV rays can have long-term effects. The AOA warns that too much sun over time can result in the possibility of a cataract and could cause damage to the retina, both which can result in vision problems and the necessity for surgery in the future. The more your toddler's eyes are exposed to UV rays, the higher his risk for sun-related vision issues in the future.

Eye Protection

While you can't put sunscreen on a child's eyes, you can use methods to protect your toddler's vision. Some toddlers are happy to slip on a pair of UV-protection sunglasses -- look for wraparound models that protect the entire eye and that stay on your toddler's head easily. If your little one won't wear sunglasses, try a hat with wide brim to keep the sun out of his eyes while he's busy playing, suggests the Skin Cancer Foundation.

Sun Smarts

While you don't need to hide from the sun, it's important that your toddler learns how to be sun smart from the start. By cautioning him against looking directly at the sun, finding shade and explaining the use of sunscreen, sunglasses and hats, your toddler can become more enthusiastic about sun safety and less likely to damage to his sensitive eyes. According to the American Academy of Pediatrics, one-quarter of lifetime sun exposure happens during childhood. By teaching your toddler sun safety, he can play outside and you can worry less.

Can Wearing Glasses Make a Toddler's Eyesight Better? by Kristen Berry, Demand Media

Wearing glasses can markedly improve a toddler's vision. According to the American Association for Pediatric Ophthalmology and Strabismus, the first five to six years of a child's life involves major vision growth and development. Not only can glasses improve your toddler's vision, they might play an important role in ensuring normal development of his vision.

Myopia -- Nearsightedness

According to research at Boston Children's Hospital, if your toddler has trouble seeing faces from across a room, or character's faces on a movie theater screen, she might be nearsighted. Nearsightedness is caused by an eyeball that is too long. This irregular shape causes incoming light rays to focus in front of your toddler's retina instead of directly on it. Distant objects appear blurry. If your toddler is nearsighted, prescription glasses will refocus the incoming light and create clearer images.

Hyperopia -- Farsightedness

Your toddler will likely have difficulty in expressing her vision problems orally. Look for signs such as the inability to fixate on or follow objects. According a nonprofit health group, Fairview Health Services in Minneapolis, if objects that are close to your toddler's line of immediate vision cause her to squint, she might be farsighted, also called hyperopia. Hyperopia is the refractive defect in which a shorter eyeball causes the image of an object to be focused behind the retina. Eyeglasses will help to correct or improve your toddler's hyperopia through adjusting the focusing power to the retina. Your toddler will have an easier time seeing close objects more clearly.

Astigmatism

Astigmatism is a common condition in which your toddler might have an abnormal curvature of her cornea. This can cause two focal points to fall in two different locations, whether your toddler is seeing an object up close, or at a distance. This can put a strain on your toddler's eyes and even cause her undue fatigue. According to Boston Children's Hospital, if your toddler has astigmatism, wearing glasses will make her vision sharper and more consistent.

Dependency

You might worry that your toddler's need for vision correction could cause her to become dependent on glasses and worsen her vision. According to the American Association for Pediatric Ophthalmology and Strabismus, the opposite might be true. If your toddler does not consistently wear the glasses prescribed, her normal vision development can be inhibited or even adversely affected. The American Association for Pediatric Ophthalmology and Strabismus recommends finding an optician who is experienced in pediatric eyewear. Your toddler's frames should fit comfortably with the eye centered in the middle of the lens.

Glasses and Contact Lenses

Why do some people need glasses and others don't?
Everyone's eyes are a little different — not just the color, but the way they work and how well they see. Sometimes all the parts of the eye don't work together the way they should. But eyeglasses or contact lenses, also called corrective lenses, can help most people see more clearly.

How Eyes Work

The eyeball includes the cornea, clear tissue that helps the eye focus; the iris, the colored part; the pupil, which lets light into the eye; the lens, which also helps the eye focus; and the retina, at the very back of the eye.
When all of the eyes' parts are working properly, a kid doesn't have vision problems. You can see because your eyes capture an image like a camera and send that image to your brain, where it can be interpreted. For instance, if there's an elephant in front of you, almost instantly, your brain says, "Hey, that's an elephant."
Your eyes need to bend light rays so the image can be focused sharply on your retina. The better your retina records the image, the more likely that your brain will interpret the image, and the more likely you will see the image clearly.
Refracting is a big word that means bending light rays. If a person has vision trouble, it's often a refractive problem. Glasses or contact lenses work so well because they can correct refractive problems. In other words, they bend the light rays in a way that lets you see more clearly.
Laser surgery also can correct some vision problems, but it's not recommended for kids because they're still growing.

Nearsighted and Farsighted — Which Is Which?

Nearsightedness and farsightedness are common refractive problems. It's easy to get the two confused:

• Nearsighted means someone can see stuff that's near, like a book, but has trouble seeing stuff that's far away.
• Farsighted means someone can see stuff that's far away, but has trouble seeing up close, like reading the print in a book.

In both cases, the image is not properly focused on the retina. With nearsightedness, the image becomes focused in front of the retina. With farsightedness, the image is focused behind the retina. The shape of a person's eyeballs also can cause refractive problems.
Another refractive problem is called astigmatism. This means that the cornea is an uneven shape, and it bends the light in different directions. This can distort what a person sees and make things look blurry.
Glasses or contact lenses correct vision because they allow the eye to focus light in the right spot on the retina — the spot that produces the clearest image. Because everyone's eyes are different, a pair of glasses that makes one person see wonderfully may look terribly blurry to someone else. You know this if you've ever tried on somebody else's glasses!
If you need glasses or contact lenses, your doctor will write you a prescription. In this case, a prescription doesn't mean medicine you'll pick up at the drugstore. A vision prescription is a piece of paper with numbers on it. The people who will make your glasses for you need these numbers to create lenses that will correct the way your eye bends light. Remember, the target is right in the center of the retina.

If you're going to get glasses, it's time to pick frames. It can be fun to try these on. Choose ones that are comfortable and sturdy. But also make sure you like them — you'll be wearing them a lot!
The lenses themselves can be made of different materials, such as safety glass or shatterproof plastic (polycarbonate). Because glass tends to be heavy and it may shatter, most glasses today are made of polycarbonate plastic. If you play sports, you may want to ask about special eyewear you can wear on the field.
Glass tends to be heavy and it can shatter. Plastic scratches easily, but it's often the best choice for kids. If you play sports, you may want to ask about eyewear you can wear on the field.
With glasses, you'll also want to find out how to clean them properly. And it helps if you have a glasses case and put them in it when you're not wearing them. The last thing you want is to sit on your new glasses.
If you're going to get contact lenses, you'll get some advice from the ophthalmologist or optician about which kind will be best for you. Some are disposable and others need to be cleaned. When you learn which type you're going to get, you can start becoming an expert in how to wear them safely and keeping them clean. The most important thing about contact lenses is good hygiene to prevent infections in your eye.
But the really fun part of new glasses or contact lenses is how well you can see. They can make your whole world look better!

How the Eye Works

The Human Eye is the Organ that Gives Us Sight 

 

The human eye is the organ which gives us the sense of light, allowing us to learn more about the surrounding world than any of the other five senses. We use our eyes in almost everything we do, whether reading, working, watching television, writing a letter, driving a car, and countless other activities. Sight is the most precious of the five senses, and many people fear blindness more than any other disability. The eye allows us to see and interpret the shapes, colors, and dimensions of objects in the world by processing the light they reflect of give off.  The eye changes light rays into electrical signals, then sends them to the brain, which interprets these electical signals as visual images. the eyeball is set in a protective cone-shaped cavity in the skull called the orbit or socket and measures approximately one inch in diameter. The orbit is surrounded by layers or soft, fatty tissue which protect the eye and enable it to turn easily. Six muscles regulate the motion of the eye. Among the more important parts of the human eye are the iris, cornea, lens, retina, conjunctiva, the macula, and the optic nerve. Cornea The cornea is the transparent, dome shaped window covering the front of the eye. It is a powerful refracting surface, providing 2/3 of the eye's focusing power. It provides the window through which we look. Iris The colored part of the eye is called the iris. It controls light levels inside the eye similar to the aperture on a camera. The round opening in the center of the iris is called the pupil. The iris is embeded with tiny muscles that dilate (widen) and constrict (narrow) the pupil size. Pupil The pupil is the black, circular opening in the center of the iris. It opens and closes in order to regulate the amount of light entering the eyeball. Crystalline Lens The purpose of the lens is to focus light onto the back of the eye. The nucleus, the innermost part of the lens is surrounded by softer material called the cortex. The lense is encased in a capsular-like bag and suspended within the eye by tiny guy wires called zonules. Vitreous The vitreous is a thick, transparent substance that fills the center of the eye. It is composed mainly of water and comprises about 2/3 of the eye's volume, giving it form and shape. Conjunctiva The conjunctiva is the thin, transparent tissue that covers the outer surface of the eye. It begins at the outer edge of the cornea, covers the visible part of the eye, and lines the inside of the eyelids. It is nourished by tiny blood vessels that are nearly invisible to the naked eye. Sclera The sclera, commonly known as "the white of the eye", is the tough, opaque tissue that serves as the eye's protective outer coat. Choroid The choroid lies between the retina and sclera. It is composed of layers of blood vessels that nourish the back of the eye. Macula The macula is located roughly in the center of the retina, temporal to the optic nerve. It is a small and highly sensitive part of the retina responsible for detailed central vision. The fovea is the very center of the macula. The macula allows us to appreciate detail and perform tasks that require central vision such as reading. Retina The retina is a very thin layer of tissue that lines the inner part of the eye. It is responsible for capturing light rays that enter the eye. These light impulses are then sent to the brain for processing, via the optic nerve. Optic Nerve The optic nerve transmits electrical impulses from the retina to the brain. It connects to the back of the eye near the macula. The visible portion of the optic nerve is called the optic disc.

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