What Are Vision Problems?
The eyes are your body's most highly developed sensory organs. In fact, a far larger part of the brain is dedicated to vision than to hearing, taste, touch, or smell combined! We tend to take eyesight for granted; yet when vision problems develop, most of us will do everything in our power to restore our eyesight back to normal.
The most common forms of vision impairment are errors of refraction -- the way light rays are focused inside the eye so images can be transmitted to the brain. Nearsightedness, farsightedness, and astigmatism are examples of refractive disorders and often occur when the eyes are otherwise healthy. Refractive errors are correctable usually with glasses, contact lenses, or refractive surgery, such as LASIK.
Other vision problems may be related to eye disease. Retinal detachment, macular degeneration, cataracts, and glaucoma are disorders of the functional eye and its processing units. These problems can lead to blurry or defective vision. The goals of treatment depend on the eye disease and may include restoring vision, halting vision loss, and preserving remaining eyesight.
Here are descriptions of common vision problems.
Nearsightedness and farsightedness have to do with the way the eye brings images into focus on the back of the eyeball, where 10 layers of delicate nerve tissue make up the retina. Images that do not focus on the retina will appear blurry. The further away images focus from the retina, the blurrier they appear.
Nearsightedness, or myopia, affects nearly 30% of the population. It is the result of images being focused in front of the retina rather than on it, so distant objects appear blurred. A nearsighted person whose eyesight has not been corrected holds a book closer to the eyes when reading and has to sit in the front of the classroom or movie theater to see clearly. The condition runs in families and affects men and women equally, usually appearing in childhood and stabilizing in the 20s.
Farsightedness, or hyperopia, is the opposite of nearsightedness. The hyperopic eye focuses images slightly behind the retina, making nearby objects appear blurry. Children may outgrow mild farsightedness as they mature and the eyeball reaches adult size. Did you know that the eye grows during childhood? The length of the eye (from front-to-back) elongates nearly one-third between birth and age five.
Light rays entering the eye first cross the clear cornea. Surprisingly, nearly two-thirds of the eye's focusing power occurs along its front surface (tear film or cornea). The normal cornea should have a semi-spherical contour similar to a soup spoon. This permits the eye to create a single focused image. If the central cornea is not symmetrical or uniform we say it is "astigmatic."
Astigmatism, often combined with nearsightedness or farsightedness, occurs when the clear cornea has a non-round curvature -- more like a teaspoon or football. Because of that, the eye lacks a single point of focus. People with astigmatism may have a random, inconsistent vision pattern, wherein some objects appear clear and others blurry. The next time you hold some shiny silverware, compare your reflection in a soup spoon to that produced by the teaspoon -- that's astigmatism! Astigmatism is usually present from birth but is sometimes not recognized until later in life. Most astigmatism is fully correctable. Also, it changes very little over time.
Near vision requires focusing or accommodation. The amount of near focusing power decreases throughout life. Presbyopia is blurred vision at a normal reading distance in someone with otherwise normal distance vision (with or without gasses). It occurs when the eye develops insufficient focusing power for reading and other near tasks. Presbyopia typically starts at about age 40 and is the reason most older adults rely on reading glasses. Bifocal spectacles permit the wearer to see objects clearly both near and distant.
Visible light rays form images that reach the brain. In order to do that, the retina converts the light signal into a nerve impulse. Think of the retina as silky wallpaper that lines the inside of the eyeball. Unlike wallpaper, however, there is no glue. Small holes can develop in areas where the retina is exceptionally thin or damaged. If that happens, the clear liquid vitreous that fills the eye can seep behind the retina and cause the wallpaper to come off. This is retinal detachment.
Although a detached retina is not painful, it is an urgent medical situation. If the retina is not reattached to the eye wall promptly, retinal cells starve and permanent blindness can result. Risk factors for retinal detachment include the following:
- Moderate or extreme nearsightedness
- Previous eye surgery or injury
- Previous retinal detachment
- Inherited thinness of retinal tissue
Color blindness is most commonly a disorder of the retina's light-sensitive photoreceptor cells, which respond to different colored light rays. There are two kinds of photoreceptors:
- Cones work best in bright light
- Rods work best in dim light
Each photoreceptor produces pigments that respond to specific colors of light.
Color vision is affected if those pigments are absent or defective or if they respond to the wrong wavelengths.
You have probably seen how paint colors are mixed at the hardware store. Color vision works much the same way because visible light is a mixture of different light rays (wavelengths). Color perception problems occur more often in men, afflicting 8% of the male population. Females tend to be the "carrier" of the trait. It is extremely rare for someone to be totally color-blind, that is, able to see only shades of gray.
Night blindness -- difficulty seeing in dim light -- occurs when rod photoreceptor cells begin to deteriorate. Rods work best in low light. There are many different forms of night blindness, but it may be linked to these conditions:
- Liver disorder
- Vitamin-A deficiency
- Inherited disease of the retina, such as retinitis pigmentosa
Eyestrain can occur simply from overusing your eyes for long periods of time. Eyestrain is discomfort that can also be due to an uncorrected refractive problem. This common vision problem may occur while you are performing distant visual activities like driving or watching a movie or during close-up tasks like reading and computer use.
Familiar symptoms of eyestrain include:
Eyestrain quickly goes away if the eyes are given a chance to rest or the refractive problem is resolved. Prolonged focusing can lead to eyestrain, such as working at the computer for hours. Children have a far more flexible focusing capacity. How often do you ever hear a child complain of eyestrain while playing video games?
If you wear prescription glasses, recurring eyestrain may be an indication that you need updated glasses or a new prescription. Eye exercises or resting the eyes every hour helps relieve eyestrain, especially when working with computers.
Other Eye Conditions That Lead to Vision Problems
There are other eye conditions that respond in varying degrees to medical and surgical treatment. The most common of these eye problems include:
The lens of the human eye focuses light so that you can see objects clearly at various distances. It contributes about one-third of the eye's focusing power and must remain transparent for clear vision. The clouding of the lens is called cataract. As we age, cataracts block or distort light entering the eye, and we experience a gradual, persistent, painless blurring of vision, as though we are looking through a haze. Cataract vision may be worse in dim light. Glare is a common problem for cataract patients who need to drive at night.
Cataracts are the leading cause of blindness, accounting for more than 20 million cases worldwide. Cataract surgery is the most frequently performed surgery in the U.S. with about 3 million procedures performed every year. The procedure can successfully restore lost eyesight in most cases. Once the cloudy lens is removed, the surgeon implants a transparent artificial lens to take its place.
The conjunctiva -- the moist, transparent membrane that covers the eyeball and your inner eyelid -- can become inflamed for various reasons. Most cases of conjunctivitis (commonly called pink eye) run a predictable course, and the inflammation usually clears up in a few days. Although infectious conjunctivitis can be highly contagious, it is rarely serious and will not usually harm vision permanently if detected and treated promptly.
There are several forms of infectious conjunctivitis:
- Bacterial conjunctivitis usually infects both eyes and produces a heavy discharge of pus and mucus. It is treated with antibiotic eye drops.
- Viral conjunctivitis usually starts in one eye, causing lots of tears and a watery discharge. The other eye follows a few days later. Like a common cold, this infection will clear up without treatment.
- Ophthalmia neonatorum is a rare acute form of conjunctivitis in newborn babies. The infection is acquired from the mother during delivery. It must be treated immediately by a doctor to prevent permanent eye damage or blindness. These infants often have infections elsewhere, such as in the lungs.
More than 2 million adult Americans suffer from glaucoma, making it one of the leading causes of irreversible vision loss. Types of glaucoma include the following:
- Chronic open-angle glaucoma (COAG), which accounts for 90% of all cases in the U.S., usually appears in middle age and seems to have a genetic component.
- Acute closed-angle glaucoma accounts for less than 10% of cases of glaucoma, but it may come on quickly, be quite painful, and require urgent medical attention.
- Secondary glaucoma is associated with other eye diseases or medical conditions, trauma to the eye, or the use of steroid drugs.
Doctors often refer to chronic open-angle glaucoma as the "silent thief of sight" because it comes on gradually to steal vision. Damage to the delicate nerve layers of the retina are caused by elevated pressure inside the eye. Most COAG patients have no symptoms whatsoever and can experience profound loss of visual function before it is identified. Regular eye checkups usually include measuring eye pressure and other tests in order to identify glaucoma. Unfortunately, half of all Americans with high eye pressure are unaware of the problem.
If you have sudden, severe pain in your eyes, blurred vision, or rainbow halos -- along with headache, nausea, or vomiting. and a non reactive large pupil -- it may be an attack of acute closed-angle glaucoma. If left untreated, acute closed-angle glaucoma can damage the optic nerve, which carries visual images from the eye to the brain, causing irreversible blindness.
Secondary glaucoma is the result of another eye disease or medical disorder, including the following:
- Uveitis (inflammation of the inner eye)
- Eye injury
- Bleeding inside the eye
- Eye tumor
- Diabetes (neovascular glaucoma)
- Congenital problems
- An extremely mature cataract
- Steroid medications
People with diabetes are susceptible to neovascular glaucoma, a particularly severe form of secondary glaucoma caused by an abnormal proliferation of blood vessels. Congenital glaucoma is a rare problem in babies and requires surgery to preserve eyesight.
Macular degeneration is the leading cause of vision loss in the U.S., with millions of older Americans showing some sign of the disorder. Because the symptoms usually do not appear in people under 55 years of age, the disorder is more accurately referred to as age-related macular degeneration (AMD).
Since the macula is the central part of the retina, AMD affects central vision, the vision you need for reading and close work like sewing. If you were looking at a photograph, you would not be able to see the middle of the picture but could still see the edges (preserved peripheral vision). The disorder occurs in two forms, dry and wet. The less common wet form of AMD requires immediate medical attention. Any delay in treatment may result in loss of your central vision.
Crossed Eyes, Wall Eye (Strabismus), and Lazy Eye (Amblyopia)
As your baby grows and develops, so do his eyes. During the first few months of life, an infant does not have crisp, clear vision. Thereafter, the eye's focusing mechanisms and eye movements rapidly develop as the eye and brain develop the visual apparatus. By about the age of 6 months, both eyes should consistently work together, allowing your baby to see both near and far away targets. The infant's eyes should be aligned, both looking at the same object.
However, in some situations the eyes do not appear to work together. One eye may tend to drift inward or outward some or all of the time. Prompt evaluation by an eye specialist is essential to determine whether any suspected drifting is due to a muscle imbalance or an internal eye problem that interferes with good eyesight.
Simply stated, the eye doctor needs to determine how well each eye sees and why the eyes do not appear straight. Parents will be relieved to know that the eye doctor's exam can find the answers without any help from the baby! Any problems that are identified need to be addressed in order to preserve good eyesight in both eyes. Misalignment of the eyes may also be the result of the following:
- Birth trauma
- Brain injury
- Cerebral palsy
- Congenital maldevelopment
- Neurologic problems
The medical term for misaligned eyes is strabismus. There are six different muscles that are attached to each eye to help it turn and rotate. The eyes may not appear straight because one or more muscles are pulling too hard or other muscles are too weak. If the eyes turn inward leading to "crossed eyes" we call it esotropia. If they turn outward, called "wall eyes," then the condition is labeled exotropia. There are different treatments for strabismus depending on the specific cause. Some cases are managed with eye muscle surgery, some simply need glasses.
Amblyopia (Lazy Eye)
If strabismus happens to an adult, perhaps after a trauma to the head or after a stroke, the person is likely to experience double vision. Double vision occurs because the two eyes are looking at different images. In an infant or a child, the brain will not tolerate double images and will shutdown the vision in the weaker eye. This involuntary loss of vision is called "lazy eye" or amblyopia. Here's another way to say it: Amblyopia is a healthy eye that does not see. Only infants and children develop amblyopia; and the vision loss can be reversed with therapy if the contributing eye problem is corrected early enough during childhood -- typically before the age of 7.
Not every case of strabismus develops amblyopia, and not all cases of amblyopia are due to strabismus. For example, an infant with a dense congenital cataract in one eye will develop "lazy eye" unless the cloudy lens is removed
Amblyopia is a serious problem for children. As long as the underlying eye problem remains untreated, the vision in the weaker eye does not develop fully. Lazy eye can also result from other eye problems, such as:
- Ptosis (drooping of the eyelid).
- A significant refractive error in one eye. If an infant has one eye that has significantly more uncorrected nearsightedness, farsightedness, or astigmatism than the fellow eye, amblyopia can develop.
If detected early, amblyopia can be reversed by first treating the underlying cause. Then, with patching and/or eye drops applied to the better eye, the weaker eye can be forced to recover useful function.