According to the Centers for Disease Control, there are nearly 800,000 work-related eye injuries each year. Every day, approximately 2,000 U.S. workers receive medical treatment for eye injuries related to or sustained at work. While vision loss is one of the 10 most common disabilities, 90 percent of eye injuries are preventable.
By Liz Segre; eye illustration by Stephen Bagi
The human eye has been called the most complex organ in our body. It’s amazing that something so small can have so many working parts. But when you consider how difficult the task of providing vision really is, perhaps it’s no wonder after all.
How the Eye Works
In a number of ways, the human eye works much like a digital camera:
Light is focused primarily by the cornea — the clear front surface of the eye, which acts like a camera lens.
The iris of the eye functions like the diaphragm of a camera, controlling the amount of light reaching the back of the eye by automatically adjusting the size of the pupil (aperture).
The eye’s crystalline lens is located directly behind the pupil and further focuses light. Through a process called accommodation, this lens helps the eye automatically focus on near and approaching objects, like an autofocus camera lens.
Light focused by the cornea and crystalline lens (and limited by the iris and pupil) then reaches the retina — the light-sensitive inner lining of the back of the eye. The retina acts like an electronic image sensor of a digital camera, converting optical images into electronic signals. The optic nerve then transmits these signals to the visual cortex — the part of the brain that controls our sense of sight.
Eye anatomy
Other parts of the human eye play a supporting role in the main activity of sight:
Some carry fluids (such as tears and blood) to lubricate or nourish the eye.
Others are muscles that allow the eye to move.
Some parts protect the eye from injury (such as the lids and the epithelium of the cornea).
And some are messengers, sending sensory information to the brain (such as the pain-sensing nerves in the cornea and the optic nerve behind the retina).
Ultraviolet (UV) radiation and blue light (also called high-energy visible, or HEV, light) from sunlight appear to increase the risk of multiple age-related eye problems, including cataracts and macular degeneration. Researchers say the more exposure you’ve had to the sun’s harmful UV and HEV rays during your lifetime, the more at risk you may be for these sight-threatening conditions.
Because children tend to spend more time outdoors than most adults, some experts say nearly half of a person’s lifetime exposure to ultraviolet radiation can take place by age 18. (Other research cited by The Skin Cancer Foundation suggests the amount of lifetime exposure to UV radiation sustained by age 18 is less than 25 percent.)
Also, children are more susceptible to damage to the light-sensitive retina at the back of the eye from UV rays because the lens inside a child’s eye is less capable of blocking UV than an adult lens, enabling more of this harmful radiation to penetrate deep into the eye.
And nearly all high-energy blue light reaches the retinas of children and adults alike, because the corneaand lens of the human eye are not capable of absorbing these rays, which have been shown to damage photosensitive cells of the retina in laboratory studies.
These factors make it very important for all children, even infants, to wear UV- and HEV-blocking sunglasses anytime they are outdoors in daylight hours. This is true even on cloudy and overcast days, because most UV rays (which are invisible) and some HEV rays can penetrate cloud cover.
By investing in quality children’s sunglasses, you are helping your kids enjoy a lifetime of good vision.
According to Prevent Blindness America, children’s sunglasses should block 99 to 100 percent of both types of untraviolet rays: UVA and UVB.
UVA is lower-energy ultraviolet radiation that can penetrate skin and eyes more deeply. UVA rays tan your skin, but they also cause your skin to wrinkle and show other signs of “photo-aging.” And because UVA rays can penetrate the eye, they have been implicated in the development of both cataracts and macular degeneration.
UVA rays account for up to 95 percent of solar UV radiation reaching the Earth’s surface, according to the Skin Cancer Foundation.
UVB is high-energy ultraviolet radiation that causes your skin to burn. The cornea blocks most UVB rays from entering the eye, protecting internal eye tissues from these high-energy rays. But overexposure to UV light can cause a serious and painful “sunburn” of the cornea called photokeratitis, which can cause a temporary loss of vision that is commonly called “snow blindness.”
SEE ALSO: Should Your Teen Wear Contacts? Click here to learn more >
In addition to causing eye problems, both UVA and UVB rays can cause skin cancer of the face, including the delicate skin of the eyelids and the area around the eyes. UV exposure also has been associated with growths on the surface of the eye called pingueculae and pterygia.
Be wary of children’s sunglasses with labels that say the lenses, “block UV rays,” but don’t specify the actual percentage of UV radiation the lenses absorb. In some cases, your eye care practitioner can use an optical instrument to determine the exact level of UV protection your child’s sunglasses provide.
Also, be aware that UV radiation penetrates clouds. Encourage your kids to wear their sunglasses even on overcast days to protect their eyes.
In addition to having lenses that block 100 percent of the sun’s UVA and UVB rays and a significant amount of potentially harmful blue light, most eye doctors recommend children’s sunglasses also have these desirable features:
For superior UV protection, it’s a good idea for kids to wear a wide-brimmed hat as well as sunglasses when spending a lot of time outdoors on sunny days. Researchers say a hat that shades the eyes and face can cut the amount of UV exposure in half. And don’t forget the sunscreen, too!
Many inexpensive children’s sunglasses provide excellent UV protection. This is especially true if they include polycarbonate lenses, because the polycarbonate lens material blocks 100 percent of UV rays without the need for added lens filters or coatings.
But cheap sunglasses for kids can pose other risks. In the recent past, the U.S. Consumer Product Safety Commission has required the recall of several brands of cheap sunglasses for children that had surface paint containing unacceptable levels of lead. And the frames, hinges and lenses of cheap children’s sunglasses often are not as durable as the components of quality sunglasses for children.
For your child’s safety and to get the best quality children’s eyewear with the best warranty, visit us at Heritage Eye, Skin & Laser Center.
Each day, approximately 10,000 Americans turn 65, and one in six adults this age and older has a vision impairment that cannot be corrected with glasses or contact lenses. An estimated 2.9 million Americans have low vision, which makes it difficult or impossible for them to accomplish activities such as reading, writing, shopping, watching television, driving a car or recognizing faces. Low vision can be caused by eye diseases that are more common in older people, such as macular degeneration, glaucoma and diabetic retinopathy. Fortunately, there are many strategies and resources available to people with low vision that can help them overcome these challenges.
Dr. Kenneth Miselis, M.D. offers the following recommendations for older adults with low vision to help make the most of their remaining sight and keep their independence.
Dr. Kenneth Miselis, M.D., Medical Director and Surgeon for Heritage Eye, Skin & Laser Center, suggests, “If you have low vision, it doesn’t mean you have to give up your activities, but it does mean finding new ways of doing them. If you think you may have low vision, see an ophthalmologist right away. The faster you receive care, the faster you can return to doing the things you enjoy and do them more independently.
University of Utah bioengineers recently discovered that our understanding of language may depend more heavily on vision than previously thought: under the right conditions, what you see can override what you hear. These findings suggest artificial hearing devices and speech-recognition software could benefit from a camera, not just a microphone.
“For the first time, we were able to link the auditory signal in the brain to what a person said they heard when what they actually heard was something different. We found vision is influencing the hearing part of the brain to change your perception of reality – and you can’t turn off the illusion,” says the new study’s first author, Elliot Smith, a bioengineering and neuroscience graduate student at the University of Utah. “People think there is this tight coupling between physical phenomena in the world around us and what we experience subjectively, and that is not the case.”
The brain uses both sight and sound when processing speech. However, if the two are slightly different, visual cues dominate sound. This phenomenon is named theMcGurk Effect for Scottish cognitive psychologist Harry McGurk, who pioneered studies on the link between hearing and vision in speech perception in the 1970s. The McGurk Effect has been observed for decades. However, its origin has been elusive.
In the new study, which appears in the journal PLOS ONE, the University of Utah team pinpointed the source of the McGurk Effect by recording and analyzing brain signals in the temporal cortex, the region of the brain that typically processes sound.
In the study, four test subjects were then asked to watch and listen to videos focused on a person’s mouth as they said the syllables “ba,” “va,” “ga” and “tha”. Depending on which of three different videos were being watched, the patients had one of three possible experiences as they watched the syllables being mouthed. The motion of the mouth matched the sound, the motion of the mouth obviously did not match the corresponding sound, and the motion of the mouth only was mismatched slightly with the corresponding sound.
By measuring the electrical signals in the brain while each video was being watched, Smith and Greger could pinpoint whether auditory or visual brain signals were being used to identify the syllable in each video. When the syllable being mouthed matched the sound or didn’t match at all, brain activity increased in correlation to the sound being watched. However, when the McGurk effect video was viewed, the activity pattern changed to resemble what the person saw, not what they heard. Statistical analyses confirmed the effect in all test subjects.
“We’ve shown neural signals in the brain that should be driven by sound are being overridden by visual cues that say, ‘Hear this!’” says Greger. “Your brain is essentially ignoring the physics of sound in the ear and following what’s happening through your vision.”
Greger was senior author of the study as an assistant professor of bioengineering at the University of Utah. He recently took a faculty position at Arizona State University.
The new findings could help researchers understand what drives language processing in humans, especially in a developing infant brain trying to connect sounds and lip movement to learn language. These findings also may help researchers sort out how language processing goes wrong when visual and auditory inputs are not integrated correctly, such as in dyslexia, Greger says.
As an ophthalmologist, Kenneth Miselis, M.D., sees much more about his patients’ health than just their eyes. Thanks to the clues the eyes provide, he regularly alerts patients to possible autoimmune diseases like rheumatoid arthritis and lupus, monitors progression of their diabetes, and once even suspected, correctly as it turned out, that a patient had a brain tumor on the basis of the pattern of her vision changes.
Because the body’s systems are interconnected, changes in the eye can reflect those in the vascular, nervous and immune system, among others. And because the eyes are see-through in a way other organs aren’t, they offer a unique glimpse into the body. Blood vessels, nerves and tissue can all be viewed directly through the eye with specialized equipment.
With regular monitoring, eye doctors can be the first to spot certain medical conditions and can usher patients for further evaluation, potentially leading to earlier diagnosis and treatment. Clots in the tiny blood vessels of the retina can signal a risk for stroke, for example, and thickened blood-vessel walls along with narrowing of the vessels can signal high blood pressure. In some cases, examining the eye can help confirm some of the diagnoses or help differentiate disorders from each other.
“There’s no question the eye has always been the window to the body,” says Dr. Japjeet Gill, Optometrist at Heritage Eye, Skin & Laser Center. She adds, “Anyone with any visual changes should be seen right away.”
Scientists are working to advance their knowledge of what the eye can reveal about diseases. For instance, researchers are studying how dark spots on the back of the eye known as CHRPE, or congenital hypertrophy of the retinal pigment epithelium, are associated with certain forms of colon cancer, and how dementia-related changes are signaled in the eye, such as how the eye reacts to light.
The eye’s job is to deliver vision by converting incoming light information into messages that the brain can understand. But problems in vision can indicate a problem outside of the eye itself.
One critical structure in the eye is the retina, which allows us to experience vision. It is made of brain tissue and contains many blood vessels. Changes in vessels in other parts of the body are reflected in the retina as well, sometimes more noticeably or sooner than elsewhere in the body.
The eyes can help predict stroke risk, particularly important to people with heart disease and other stroke risk factors. That is because blood clots in the arteries of the neck and head that might lead to stroke are often visible as retinal emboli, or clots, in the tiny blood vessels of the eye, according to the National Eye Institute.
The immune system’s interaction with the eyes can be telling, too, yielding information about autoimmune diseases or infections in the rest of the body. Sometimes eye symptoms may appear before others, like joint pain, in patients.
For instance, inflammation in the optic nerve can signal problems in an otherwise healthy, young person. Along with decreased vision and sometimes pain, it can suggest multiple sclerosis. If the optic disc, a portion of the optic nerve, is swollen, and the patient has symmetrical decreased field of vision, such as a decreased right visual field in both eyes, they may need an evaluation for a brain tumor—a rare circumstance.
If immune cells like white blood cells are seen floating in the vitreous of the eye, it could signal a local eye infection or one that has spread throughout the body.
Diabetes is one disease that can cause major changes in the eye. In diabetic retinopathy, a common cause of blindness, blood vessels hemorrhage and leak blood and fluid. When blood vessels don’t function properly, they can potentially cause eye tissue to be deprived of oxygen and to die, leaving permanent vision damage.
Also, in diabetic patients additional blood vessels may grow in the eye, anchoring themselves into the sticky gel known as the vitreous, which fills a cavity near the retina. This condition can cause further problems if the retina tears when it tries to separate from the vitreous—a common occurrence as people age—but is tangled by growth of new blood vessels.
Usually diabetic patients who come in for eye exams already know they have the disease, and the primary purpose of an eye exam is to make sure they don’t have diabetic retinopathy, or if they did have it, that the condition hasn’t progressed, say the eye doctors at Heritage. “Once in a while there is a patient who has noticed vision changes but doesn’t realize he or she has diabetes until alerted during an eye exam that there are signs of the eye disease that are consistent with the condition,” says Dr. Miselis, Medical Director, Ophthalmologist, and Surgeon at Heritage.
Dr. Miselis recommends eye examinations whenever individuals notice any vision changes or injury. Adults with no symptoms or known risk factors for eye disease should get a base line exam by age 40 and return every year for evaluation.
Eye cosmetics are intended to make eyes more attractive, or in some cases to cleanse the eye area. One thing they shouldn’t do is cause harm. Most are safe when used properly. However, there are some things to be careful of when using these products, such as the risk of infection, the risk of injury from the applicator, and the use of unapproved color additives.
The following information provides an introduction to some safety concerns related to eye cosmetics.
Keep it clean!
Eye cosmetics are usually safe when you buy them, but misusing them can allow dangerous bacteria or fungi to grow in them. Then, when applied to the eye area, a cosmetic can cause an infection. In rare cases, women have been temporarily or permanently blinded by an infection from an eye cosmetic.
Occasionally, contamination can be a problem for some eye cosmetics even when they are new. The FDA has important alerts in effect for cosmetics. To read the alerts or check for makeup recalls, please visit the FDA website: http://www.fda.gov/Cosmetics/ProductandIngredientSafety/ProductInformation/ucm137241.htm
In addition, use the following information when purchasing and using eye makeup: