How the Eyes Work
Every morning, we open our eyes and become immersed in a wealth of visual information. The eyes and related brain structures are a complex system that allows us to experience visual information from the surrounding world. It is easy to take clear vision for granted, but even subtle changes in the structure or functioning of the eyes can disrupt our sight. An eye care provider conducts a thorough eye exam to ensure that these components are functioning together well.
Basic Eye Anatomy
The eyeball is not a single, spherical structure as is commonly thought. It consists of a smaller, curved portion called the cornea that attaches to a larger, roughly spherical structure called the sclera (the white of the eye). The eyeball is filled with a jelly-like substance called the vitreous fluid.
Toward the front of the eye are three essential structures: the iris, pupil, and lens. The iris is the colored part of your eye. It can open and close to determine how much light to let in through the pupil, the black hole in the center of your eye. Finally, the lens is a flexible, convex structure that changes shape to direct light rays in different directions within the eye.
At the back of the eyeball is a layer of tissue called the retina. The retina consists of millions of photosensitive cells that react to certain types of light. Cone cells are clustered toward the center of the retina, and react to colors and details in bright light. Rod cells, which are spread toward the periphery of the retina, react to dim lighting conditions.
How the Eyes Facilitate Vision
When light enters the eye through the pupil, it passes through the lens, which changes shape to ensure that the light rays hit the retina. When the light rays reach the back of the eye, it stimulates the rod and cone cells to fire. Cone cells detect fine details and color in the center of your visual field. Rod cells detect edges in peripheral vision and allow us to perceive shapes in dim light.
The rods and cones in your retina convert light energy into electrical signals, which exit the eye through the optic nerve, located just below the center of the retina. The optic nerve carries visual information to the occipital cortex in the very back of your brain, where it is processed to result in a rich visual experience.
If any part of this complex arrangement functions improperly, vision is impaired. Thus, it is essential to receive regular optometry exams to have your eye structures and visual abilities checked.
The Effects of the Sun on Our Eyes
Optometry warnings about the damaging effects of ultraviolet radiation on our eyes have not yet reached the degree of public awareness of that of skin damage. Yet, the sun can be just as damaging upon our eyes with unprotected exposure. Short-term exposure to very bright sunlight can result in a type of sunburn to our eyes regardless of the season. Photokeratitis -- also known as "snow blindness" and "flash burns" -- is a sunburn to the eye's cornea and conjunctiva, the membranes lining the eyelids and the outermost lining of the eye. Like a skin sunburn, the initial inflammation, pain and redness can last up to 48 hours before subsiding. Treatment such as cold cloths over the eyes and an over-the-counter anti-inflammatory medication can help relieve some of the painful symptoms, but the best treatment is prevention best obtained by wearing sunglasses and a hat with a brim.
The Damage Adds Up
One day on the beach and a couple of days of sore eyes doesn't seem like much, but eye care providers warn that the effect is cumulative and the damage increases with every day of unprotected overexposure. Long-term damage goes beyond crow's feet from squinting in the bright sunlight. Years of unprotected exposure to the sun can result in increased chances of cataracts, damage to the retina, macular degeneration, cancer of the eye itself and cancer of the eyelid. Pterygium, a recurring condition where the conjunctiva grows over the cornea to restrict vision, requires repeated surgeries to keep in check is also common.
Not All Sunglasses Are Equal
Any pair of sunglasses is better than wearing none at all, but not all sunglasses provide the same degree of protection to the eye. Ask your eye care provider for recommendations to fit your lifestyle and your budget.
Protecting Your Eyes from Damage
Of our five senses, humans rely on vision most strongly. Our everyday experience of the world is colored by our ability to see, our memory draws heavily upon visual information, and many activities of daily living are challenging without sight. As a result, it is essential to protect your eyes from damage. Regular visits to an eye care provider allow you to receive a professional eye exam that checks for damage due to inadequate eye protection.
Americans are spending more time than ever in front of screens. From checking email on smartphones to staring at a computer screen in your office to watching TV in the evenings, too much screen use can cause eye strain. Experts recommend taking at least five minutes per hour to relax your eyes and alleviate strain. Go for a brief walk or focus on distant objects to reduce eye strain before returning to the task at hand.
Dust, Wind, and other Environmental Stressors
It is easy for eyes to become damaged by windy conditions, blowing dust, air pollutants, and other small particles in the air. When facing dusty or windy conditions, eye drops or safety glasses can protect your eyes from damage. Contact wearers should opt for glasses to prevent particles from irritating the surface of your eyes. Whenever possible, stay indoors on very windy or dusty days to prevent eye damage. If your eyes become very irritated, visit the eye doctor for a thorough optometry exam and treatment recommendations.
Everyone knows that UV rays cause sunburns, but did you know that UV exposure damages your eye tissue as well? Lengthy, intense exposure to UV rays may increase your risk of macular degeneration, cataracts, and other eye conditions that affect your vision. To stay safe, find a pair of sunglasses that block 100% of UVA and UVB rays. Darker lenses or more expensive styles do not always translate to better UV protection. When possible, choose wrap-around styles that do not let light in from the side. Sunglasses are not just for summertime or bright days -- UV damage can occur year-round and can be especially bad during the wintertime when sunlight reflects off of ice and snow.
In general, the best policy is to avoid taking chances with your eye health. Wear proper protection when heading outside, playing sports, and working with dangerous tools or chemicals. Your eyes are designed to last a lifetime; treat them well, and you can avoid major vision problems that affect everyday life.
The human visual system is an amazing network of anatomical structures. Even minor changes in the structure or function of a component of the eye can significantly affect visual acuity. Because we rely so heavily on our visual system to receive and process information, it is essential to keep the eyes functioning properly. Visit your eye care provider regularly for a vision check-up to ensure any of these common eye conditions are diagnosed and treated properly.
Common Eye Conditions
Dry eye is a highly common -- and vexing -- eye condition. Dry eye develops when your eye no longer produces an appropriate tear layer. Tears lubricate the surface of the eye, protect against infection, and ensure clear vision. Dry eye can be associated with age, environmental irritants, certain medications, and medical conditions such as diabetes, thyroid problems, and rheumatoid arthritis. An eye care provider may recommend medications, dietary changes, or surgery to rectify the problems associated with dry eye.
If the cornea, the front part of the eyeball, is shaped incorrectly, light does not focus properly on the retina. This leads to blurred vision regardless of the distance you are from an object. Although most people have a slight amount of astigmatism, it becomes problematic when it causes visual distortions, blurred vision, headaches, or eye discomfort. Fortunately, astigmatism is easily corrected by prescription glasses or contacts.
Many people do not have perfect 20/20 vision. When their visual deficits cannot be improved with the best possible glasses, individuals are considered to have low vision. Low vision may be associated with severe medical conditions or trauma to the eye. An optometry exam can identify cases of non-correctable low vision and options for low vision care.
As your eyes get older, the lens of your eye may become cloudy. By age 80, nearly half of individuals develop some lens clouding, referred to as cataracts. Cataracts can also form through genetic disorders or other medical conditions. Symptoms include blurred vision, changes in colored vision, poor night vision, or double vision. The early symptoms of cataracts can be reduced by changes in lenses or lighting conditions. In later stages, surgical removal of the cataract may be warranted.
Glaucoma does not refer to damage to the eyeball itself, but rather to the optic nerve that carries visual information to the brain. Changes in eye pressure may constrict the nerve, causing glaucoma. Medicated eye drops are a common treatment, but surgery may be necessary in severe cases.
If you experience any change in vision, visit an eye care provider immediately. An eye exam is essential to monitoring eye health, preserving your vision for life.
Intricate and complex, the eyes take in and process light and communicate information to the brain through electronic impulses. Several diseases and conditions - viral, bacterial, and genetic - affect the eyes and their ability to function properly. Any sign of unusual eye symptoms should prompt a visit with an eye care professional.
Cytomegalovirus (CMV) Retinitis
Associated with acquired immunodeficiency syndrome (AIDS), this disease also affects people whose immune systems have been compromised for other reasons like chemotherapy or bone marrow transplant. The virus invades the retina and damages photoreceptor cells, causing floaters, blurry vision, flashes, and/or decreased peripheral vision. Left untreated, CMV retinitis leads to detached retina and blindness.
An eye condition in which the cornea thins, weakens, and loses its normal round shape, keratoconus causes astigmatism and nearsightedness. Though the exact cause is not yet known, research has shown that an imbalance in enzymes within the cornea might cause keratoconus. No cure exists for keratoconus, but effective methods of treatment which slow its progression and reduce symptoms have been developed.
Fuchs' Corneal Dystrophy
An inherited disease, Fuchs' corneal dystrophy causes endothelial cells which regulate fluid in the cornea to die. This leads to corneal edema (swelling). Symptoms include glare, blurred or distorted vision, painful blisters on the cornea, a cloudy or hazy cornea, corneal swelling, and corneal thickening.
A genetic eye disorder, macular dystrophy damages the photoreceptor cells located on the macula (the center of the retina), leading to a loss of central vision. Central vision is used to look straight ahead and is necessary for activities such as reading, driving, and recognizing faces. There are two types of macular dystrophy: Best disease, which affects children, and adult onset macular dystrophy, which occurs in adulthood.
Retinitis Pigmentosa (RP)
A rare, inherited disease, RP causes the photoreceptor cells in the retina to progressively degenerate. This degeneration first narrows the field of vision and leads to decreased night vision. Eventually, photoreceptors deteriorate so extensively that the disease causes near blindness with only slight peripheral and a small area of central vision remaining.
A form of inherited macular dystrophy which affects children and young adults, Stargardt disease is characterized by the death of photoreceptor cells on the macula (the center of the retina). Sufferers usually lose central vision while peripheral vision remains intact.
Vision, one of our five senses, is perhaps the most relied upon in our daily lives. For this reason, eye health is essential. Vision is one of the most delicate systems in the human body, so any unusual symptoms or sensations should be brought to the attention of an eye care professional immediately to ensure proper treatment and continued function. The following common eye symptoms are a few which may require a visit to and an examination by your eye care professional.
Sleep in the Eyes
Also referred to as eye matter or eye discharge, a little sleep in the eyes upon waking is a normal function of the eye, produced by your body's mechanism for clearing the eyes of any bacteria or debris such as allergens or cosmetics. A change in your eye's normal discharge (consistency, frequency, or amount), however, can point to an eye infection which requires prompt treatment. Conjunctivitis (bacterial, viral, or allergic) is the condition most commonly associated with abnormal eye discharge.
Also called light sensitivity, photophobia is characterized by a sensitivity or intolerance to bright light. In mild cases, one might need to squint in bright light, but in serious cases of photophobia, bright light causes severe pain in the eyes. Corneal abrasion, dry eyes, scleritis, conjunctivitis, encephalitis, meningitis, and subarachnoid hemorrhage all cause photophobia. Some causes of photophobia are not considered serious medical problems, but sometimes this symptom accompanies conditions which are medical emergencies. Any instance of light sensitivity should be brought to the attention of an eye care professional.
Small spots, squiggly lines, strands, or ring-like objects which appear in the field of vision are called floaters. Especially apparent in bright environments, floaters are most often a benign annoyance. They can, however, appear in conjunction with more serious underlying conditions such as eye tumors, retinal detachment, vitreous hemorrhage, or a retinal tear. Anyone experiencing floaters should seek treatment with an eye care professional.
Eye Procedures and Treatments
Many eye disorders that cause total blindness can be treated successfully enough to prevent this final outcome. Modern technologies and techniques allow eye care providers to perform advanced procedures to reverse, arrest, or at least slow vision loss. Some of these procedures include:
Corneal transplant - Individuals who suffer from weak, damaged, or deformed corneas may opt for a corneal transplant after other corrective procedures have failed. Depending on the extent of the problem, your eye doctor may extract the entire central portion of the cornea or just the epithelial layer beneath the topmost layer of tissue. You will then receive a donor cornea or a biocompatible synthetic cornea. While you may be able to return to your daily life activities after a few weeks, total recovery can take a year or more.
Corneal collagen crosslinking - People with keratoconus suffer from weak collagen bonds in their corneal tissue. Corneal collagen crosslinking addresses this problem by using a combination of riboflavin and UV-A rays to strengthen the bonds between the collagen fibers. This type of procedure is referred to as CXL or C3R; while it does not reverse the bulging caused by keratoconus, it might slow the disorder and thus help you avoid a corneal transplant.
Intacs for keratoconus - If you suffer from a bulging of the cornea known as keratoconus, you may be able to flatten that bulge out with the aid of Intacs. These tiny, sliver-shaped inserts are fitted into an incision around the periphery of the cornea. They exert just enough outward pressure to flatten the bulge back to a normal spherical shape. If you can't get satisfactory vision correction from glasses or contacts, Intacs may be the next logical choice.
Vitrectomy and other vitreoretinal procedures - The eye is filled with a clear, gelatinous substance called the vitreous humor. If foreign matter such as blood or bits of tissue are floating through this substance, you may experience vision problems. In a vitrectomy, the surgeon inserts a needle to drain out the compromised vitreous humor, replacing it with sterile saline. In addition to vitrectomy, other vitreoretinal procedures may be necessary to treat conditions ranging from retinal detachment to macular degeneration.
Vision problems can turn ordinary pursuits such as driving or reading into an impossible task. Damage to sensitive components of the eye, congenital abnormalities in the shape of the eye, or age-related changes can all contribute to vision loss. Since vision loss can be a gradual process, regular eye exams and vision screenings should be a part of every individual's personal wellness routine.
Vision problems may manifest themselves as any of the following disorders (among others):
Blurry vision - Blurry vision may be caused by a wide range of issues, ranging from dry eyes and eye strain to congenital or acquired focusing problems. Chronically dry eyes may make the visual field appear blurry, as well as a refractive error in the cornea or lens known as astigmatism. In some cases, patients recovering from eye surgery may experience blurry vision.
Double vision - Double vision, the perception of two overlapping images, occurs when the two eyes cannot bring their separate images into alignment. It may be the result of dry eyes, cataracts, eye surgery complications, or other issues. In some cases, a neurological injury or disease may create double vision.
Higher-order aberrations - These visual symptoms occur when some irregularity in the lens, cornea, or other part of the eye interferes with the normal passage and refraction of light. Cataract sufferers, for instance, typically see halos around automobile headlights at night. Other aberrations may include starburst patterns, poor night vision, blurring of images, and uncomfortable glare.
Hyperopia - Hyperopia, or farsightedness, is the inability to view close objects in focus. It is usually the result of an abnormal eyeball shape that causes incoming light to reach a focal point that would extend beyond the back of the eye.
Myopia - Myopia, or nearsightedness, occurs when the distance between the front and back of the eye is too great or the cornea has too much curvature. This causes incoming light to reach a focal point before it hits the retina, causing distant objects to appear out of focus.
Peripheral vision loss - Loss of vision around the outer edges of the vision field may occur due to glaucoma, neurological damage, a detached retina, concussions, strokes and other conditions.
Amblyopia - Amblyopia, or "lazy eye," occurs when one eye does not develop its visual acuity as thoroughly as the other. It a common childhood issues and can often be corrected with therapies to strengthen the eye.
We take a lot of aspects of our vision for granted. We expect to see nearby and faraway objects clearly, even if we require our eye care provider to prescribe eyeglasses or contact lenses to do so. A huge degree ofPain_management.jpg the information we take in about our world and our surroundings takes place visually, yet we rarely recognize and appreciate the fact. Finally, as adults we blink on average 10 to 15 times per minute or over 16,000 times during an 18-hour day. Despite all the mechanical action involved in blinking, moving one's eyes to follow a moving object, or even focusing our eyes to see a small object, most of us rarely experience eye pain. Thus, when we do experience eye pain, it is an extremely frustrating event, despite the magnitude of the pain we may feel. The pain may limit our ability to see, read, walk, watch TV or conduct many of the activities of daily living.
Common Sources of Eye Pain
• Physical or Chemical Irritants
Eye pain or irritation can come from a variety of sources. Sand or grit blown into one's eyes can cause significant discomfort until the particles are rinsed out with a neutral eye solution. The vapor of some harsh chemicals can also cause eye irritation, particularly if used in enclosed spaces. Tear gas is an example of a chemical designed to cause severe eye irritation, overactive tearing as the eyes attempt to wash the chemical away, and involuntary eyelid closure to avoid additional exposure to the irritant. An optometry evaluation may be necessary under these circumstances to help treat the exposure and prevent permanent damage.
"Snow blindness" or "flash burns" -- the eyes' equivalent of a sunburn -- can occur when we expose our eyes to bright sunlight or extremely bright lights without the protection of ultraviolet sunglasses. Just like a sunburn, the eyes may require two to three days to recover. Treatment for photokeratitis usually consists of cool compresses to the closed eyes three to four times per day, an over-the-counter anti-inflammatory medication by mouth and plenty of fluids. Like a sunburn affects the skin, photokeratitis can cause long term damage to one's visual health.
Dry Eye Syndrome
Insufficient tear production or dry eye syndrome can also cause significant eye pain and irritation. We depend upon our liquid and mucous-based tears to lubricate our eyeballs and prevent friction with each blink. When tears are absent or made in insufficient quantity, friction, irritation, and pain can result.
Some neurological conditions -- such as migraine headaches, cluster headaches or trigeminal neuralgia -- can also appear with primary symptoms of eye pain. See your eye care provider if these symptoms persist or if you are experiencing frequent or ongoing eye pain.
Frequently Asked Questions
Why do I need to see an eye care provider?
Many “silent” diseases, such as glaucoma and diabetes, can only be detected through regular eye exams. When these conditions are discovered earlier rather than later,Eyeglasses.jpg they become easier to treat or manage, allowing for better long-term preservation of eyesight.
In addition, reading glasses from the drugstore often do not work well because most people have astigmatism and/or different prescriptions in each eye. As a result, many of these individuals experience persistent eye fatigue and headaches. Forgoing the eye exam also sacrifices the opportunity to screen for treatable diseases, as mentioned above.
How often do I need to get new eye glasses?
This depends on a number of personal factors, such as changing needs, tastes or lifestyle, but you should visit your eye doctor at least once each year. If you notice problems with vision or headaches, then it’s best to consult your doctor right away for a full evaluation and new glasses, if needed.
How can I tell if I need bifocals?
Bifocals and progressive lenses are most often prescribed for presbyopia in those over age 40 and for individuals who have trouble seeing clearly both at a distance and when reading. Bifocals can also help a person who over-crosses his or her eyes when viewing close objects. An eye exam with a qualified eye doctor can assist you with determining whether bifocals are right for you.
Instead of bifocals, can I use progressive lenses and choose a smaller eye glass frame?
Yes. Progressive lenses offer more precision in your viewing range within a smaller lens diameter. However, some frames are too small for a proper fit; a trained optician can work with you to find a frame that is sized correctly for both your lens and your face shape.
Why are the lenses so thick?
The final lens thickness depends on the strength of your prescription, the size of your frame, and your personal measurements. Fortunately, recent innovations in lens designs and materials have made lenses thinner by up to 60% in some cases. If lens thickness is a concern for you, notify the optometry staff member; he or she will help you select a frame and lens that allow you to use a thinner lens.
Will I have to wear eye glasses forever?
Unfortunately, you probably will unless you elect to use contact lenses or corrective laser eye surgery. The great news is that there are lens and surgical advancements in optometry everyday.