What is amblyopia?
Amblyopia is a reduction or dimming of vision in an eye that appears to be normal. Eye disorders that affect vision can be divided into two groups:
- Refractive errors—Eye disorders in which the shape of the eye does not refract the light that enters the eye properly, resulting in blurred vision.
- Nonrefractive errors—Eye disorders that are not caused by refractive errors; rather, they are caused by eye diseases.
Refractive errors are seen in almost 20 percent of children. The following are the most common refractive errors, all of which affect vision:
- Myopia or "nearsightedness"—Myopia is the most common refractive error seen in children. Myopia means that a child can see close up, but has problems with seeing things far away. It is usually not present at birth, but begins to develop as the child gets older. It is usually noted in children around the ages of nine or 10. This might be noted in a child that cannot read the blackboard from the back of the room, but can see to write and read without a problem. Other signs and symptoms may include headaches, nausea after reading, holding books close to one's face or writing with one's head very close to the table.
- Hyperopia or "farsightedness"—The child may or may not see things close to them, but they do not have a problem seeing things far away. Squinting, eye rubbing, lack of interest in school and difficulty in reading may be seen in children with hyperopia. This condition is uncommon in children.
- Astigmatism—An abnormal curvature of the cornea occurs, resulting in decreased vision. This can start in childhood or as an adult and can be easily corrected if it is causing problems. Some signs and symptoms of astigmatism may include headache, eye strain, difficulty reading and fatigue. Depending upon the severity, eyeglasses or contact lenses may be required.
- Amblyopia or "lazy eye"—Amblyopia is a common type of visual condition that can happen even when there is no problem with the structure of the eye. The decrease in vision occurs when one or both eyes send a blurry image to the brain. Then the brain learns to see only blurry with that eye. Better treatment success is achieved when treatment is started early.
- Strabismus or "crossed-eyes"—Strabismus is one of the most common eye problems in children in which the eyes are misaligned. The eyes (one or both) may turn inward, outward, turn up or turn down. Children younger than six months of age may have a common form of strabismus that comes and goes. Most strabismus is caused by abnormality of neuromuscular (including brain) control of eye movement. Strabismus as a result of poor muscle strength in the eye is less common.The signs and symptoms of strabismus may include a child squinting their eyes, a child that cannot properly judge distance to pick up objects, a child that closes one eye to see better, dizziness, or the child's eyes move inward or outward. Early diagnosis of the underlying problem is essential in order to prevent vision loss. Treatment of strabismus may include patching the stronger eye in order to increase the strength in the weaker eye, eyeglasses, eyedrops, surgery to straighten the eyes or eye exercises.
Nonrefractive errors may be caused by the following:
- Glaucoma—The normal fluid pressure inside the eyes (intraocular pressure, or IOP) slowly rises as a result of the fluid aqueous humor—which normally flows in and out of the eye—not being able to drain properly. Instead, the fluid collects and causes pressure damage to the optic nerve (a bundle of more than one million nerve fibers that connects the retina with the brain) and loss of vision. Glaucoma is classified according to the age of onset. Glaucoma that begins before the child is three years old is called infantile or congenital (present at birth) glaucoma. Glaucoma that occurs in a child is called childhood glaucoma.Signs and symptoms of glaucoma may include excessive tearing, light sensitivity (photophobia), closure of one or both eyes in the light, cloudy enlarged cornea, one eye may be larger than the other and vision loss. Treatment of glaucoma usually involves surgery. Without treatment, blindness may occur.
- Cataract—A cataract is a clouding or opaque area over the lens of the eye, an area that is normally transparent. As this thickening occurs, it prevents light rays from passing through the lens and focusing on the retina, the light sensitive tissue lining located in the back of the eye. This clouding is caused when some of the protein which makes up the lens begins to clump together and interfere with vision. Cataracts can affect either one eye (unilateral) or both eyes (bilateral). Cataracts in children are uncommon. A child may be born with the disease (congenital), or it may develop later in life (acquired). Possible causes of cataracts include the following:
- Steroid use
- Other childhood diseases such as rheumatoid arthritis
- Complications from other eye diseases, such as glaucoma
The majority of congenital cataracts are present in children who also have other eye problems or other health problems. In approximately 25 percent of children born with congenital cataracts, the condition is due to a genetic cause, such as a metabolic disorder (caused by an inherited enzyme deficiency) or a chromosome abnormality (such as, Down syndrome).
- Retinoblastoma—Retinoblastoma is a rare cancer of the retina. The retina is the innermost layer of the eye, located at the back of the eye, that receives light and images necessary for vision. About 250 children in the U.S. are diagnosed with this type of cancer each year. It mostly occurs in children under the age of five; the highest incidence of the disease occurs between infancy and age two. Both males and females are affected equally. Retinoblastoma can occur in either eye; however, in about 25 to 30 percent of the cases, the tumor is present in both eyes. Signs and symptoms of retinoblastoma may include:
- Leukocoria—A white light reflex that occurs at certain angles when light is shown into the pupil.
- Strabismus (also called "wandering eye" or "crossed-eyes")—A misalignment of the eyes when one or both eyes do not appear to be "looking" in the same direction.
- Pain, swelling, or redness around the eye(s)
Treatment of retinoblastoma may include:
- Surgery (removal of the eyeball which may be followed up with an artificial eye implant)
- Heat treatment (uses extreme heat directed toward cancer cells)
- Radiation therapy
- Laser therapy (uses light to destroy the blood vessels that nourish the tumor)
- Cryotherapy (uses a freezing process to destroy the tumor)
- Fitting and training for a prosthesis (artificial eye)