Health Topics A-Z

Astigmatism

Light rays entering the eye first cross the clear cornea. Surprisingly, nealy two-thirds of the eye's focusing power occurs along its front surface (tear film or cornea). The normal cornea should have a round, semi-spherical contour just like a soup spoon. This permits the eye to create a single focused image. If the central cornea is not round we say it is 'astigmatic'.

Astigmatism often combined with near - or farsightedness, occurs when the clear cornea has a non-round curvature - more like a teaspoon. Becaues of that, the eye lacks a single point of focus. People with astigmatism may have random, inconsistent vision pattern, wherein some objects appear clear and others blurry. The next time you are holding some shiny silverware compare your reflection in a round soup spoon to that produced by the teaspoon - that's astigmatism! Astigmatism is usually present from birth but is typically not recognized until later in life. Most astigmatism is fully correctable. It neither improves nor worsens over time.

Presbyopia

Up until now we've only discussed distant vision. Near vision is called accommodation. The amount of near focusing power decreases throughout life. Presbyopia is blurred vision at normal reading distance and it occurs when the eye develops insufficient focusing power for reading and other near tasks. It typically starts at about age 40 and is the reason most older adults rely on reading glasses. Bifocal spectacles permit the wearer to see clearly at near and distant objects.

Retinal detachment

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 a 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. We call this retinal detachment. Although a detached retina is not painfull, it is definitely a medical emergency. If the retina is not reattached to the eyewall promptly, retinal cells starve and permanent blindness can result. Risk factors for the condition include moderate or extreme nearsightedness, previous eye surgery or injury, previous retinal detachment, and inherited thinness of retinal tissue.

Color blindness

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) and 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, defective, or if they respond to inappropriate 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 24% of the male population. It is extremely rare for someone to be totally color-blind - that is, able to see only shades of gray.

Night blindness

Night blindness — difficulty seeing in dim light — occurs when rod photoreceptor cells begin to deteriorate. Remember, the rods are supposed to work best in low-light environments. There are many different forms of night blindness, but it may be linked to a liver disorder, a vitamin-A deficiency, or an inherited disease of the retina, such as retinitis pigmentosa.

Eyestrain

Eyestrain is a very common complaint. It is discomfort attributed to an uncorrected refractive problem and may occur while performing distant visual activities like driving or watching a movie or during-close-up tasks.

Familiar forms of eyestrain include headache, brow-ache, eye fatigue or even a pulling sensation. Eyestrain quickly dissipates if 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 spectacles, recurring eyestrain may be an indication that you need updated glasses or a new prescription. Eye exercises or resting the eyes every 30 minutes helps relieve eyestrain, especially when working with computers.

There are other eye conditions that respond in varying degrees to medical and surgical treatment. The most common eye problems include: cataracts, conjunctivitis, glaucoma, crossed or crooked eyes (strabismus), lazy eye (amblyopia), and macular degeneration.

Cataracts

The lens of the human eye focuses light so that you can see objects clearly at various distances. It contributes to approximately one-third of the eye's focusing power and must remain transparent for clear vision. The clouding of this lens is called cataract. As the developing cataract blocks or distorts the light entering the eye, one experiences a gradual, persistent, painless blurring of vision, as though you were 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 in the world, accounting for almost 20 million cases worldwide. Cataract surgery is the most frequently performed surgery in the U.S. with over one 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. Despite these remarkable advances, in the U.S. alone, an estimated 5,000 people go blind each year because of ignorance, fear or refusal to undergo a painless operation.

Conjunctivitis

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 permanently harm your vision 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 is usually limited to one eye, causing copious tears and a watery discharge. The fellow eye follows a few days later. Like a common cold, this self-limiting infection will resolve without treatment.
• Allergic conjunctivitis produces tears, itching and redness in the eyes, and sometimes an itchy, runny nose. Allergy medicines in the form of pills or eye drops will relieve these symptoms.
• Ophthalmia neonatorum is an 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 like the lungs.

Glaucoma

More than 2 million adult Americans suffer from glaucoma, making it one of the leading causes of irreversible vision loss. 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: One out of five sufferers has a close relative with the condition.

Doctors often refer to chronic open angle glaucoma as the "sneak thief in the night" because it comes on gradually to steal your 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 involve measuring eye pressure in order to identify glaucoma. Unfortunately, half of all Americans with elevated intraocular pressure are unaware of the problem.

Other forms of glaucoma are less common but no less serious. If you have sudden, severe pain in your eyes, blurred vision - along with headache, nausea or vomiting — it may be an attack of acute closed angle glaucoma. This type accounts for less than 10% of reported cases, but it comes on quickly and requires urgent medical attention. If left untreated, acute closed angle glaucoma can irreversibly damage the optic nerve, which carries visual images from the eye to the brain, causing irreversible blindness.

Secondary glaucoma is usually associated with another eye disease or medical disorder, such as an extremely mature cataract, uveitis (inflammation of the inner eye), bleeding inside the eye, an eye tumor or an eye injury. People suffering from diabetes are also 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 - 80% or cases occur by age 1 and require surgery to preserve eyesight.

Macular degeneration

Macular degeneration is the leading cause of vision loss in the U.S., with more than 13 million 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 (ARMD).

ARMD affects your central vision, meaning 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). If you are over 65, macular degeneration may already affect your central vision - the vision you need to reading and close work like sewing. The disorder occurs in two forms, dry and wet. The less common wet form of ARMD requires immediate medical attention. Any delay in treatment may result in loss of your central vision.

Crossed Eyes or Wall Eye (Strabismus) and Lazy Eye (Amblyopia)

As your baby grows and develops, so do his or her eyes. During the first few months of life, an infant does not have crisp, clear vision. Gradually, 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 some or all of the time. Prompt evaluation by an ophthalmologist is essential to determine whether any suspected crookedness is due to a muscle imbalance or because of 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 appear crooked. Parents will be relieved to know that the eye doctor's examination 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 birth trauma, brain injury, cerebral palsy, congenital maldevelopment, neurologic problems and hydrocephalus.

Strabismus - The medical term for misaligned eyes is strabismus. Did you know that there are six different muscles that are attachedto each eye to help it turn and rotate? The eyes can appear crooked 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 or "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. The term makes sensebecause the two eyes are looking at different images. In an infant or your 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 during childhood.

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