Eye disorders that affect vision can be divided into two groups, including the following:
Refractive errors. Refractive errors are 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. Nonrefractive errors are eye disorders that are not caused by refractive errors; rather, they are caused by eye diseases.
What are refractive errors?
Refractive errors are seen in almost 20% 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 9 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." Hyperopia is one type of refractive error in which the child might or might not see things close to him or her, but he or she does 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. Astigmatism is one type of visual condition in which an abnormal curvature of the cornea happens, 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 on the severity, eyeglasses or contact lenses may be needed.
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. At times, more than one of these conditions are present. Strabismus is also called "wandering eye" or "crossed-eyes." Children younger than 6 months of age may have a common form of strabismus that comes and goes. This type of strabismus may be normal. 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 his or her 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.
What are nonrefractive errors?
The following are some causes of nonrefractive errors:
Glaucoma. Glaucoma is a condition in which 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 1 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 3 years old is called infantile or congenital (present at birth) glaucoma. Glaucoma that happens 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 happen.
Cataract. A cataract is a clouding or opaque area in the lens of the eye—an area that is normally transparent. As this clouding happens, 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 interferes with vision. Cataracts can affect either one eye (unilateral) or both eyes (bilateral). Cataracts in children are uncommon.
A child may be born with cataracts (congenital), or it may develop later in life (acquired). Possible causes of cataracts include the following:
Other childhood diseases, such as rheumatoid arthritis
Complications from other eye diseases, such as glaucoma
The majority of congenital cataracts (those present at birth) are present in children who also have other eye problems or other health problems. In approximately 25% 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).
Signs and symptoms of a cataract may include the following:
White pupil on flashlight exam
Involuntary rhythmic movements of the eyes back and forth, up and down, around, or mixed (nystagmus)
Cloudy or blurry vision
Lights appear too bright and/or present a glare or a surrounding halo
Treatment of cataracts usually involves surgery.
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 happens in children under the age of 5; the highest incidence of the disease happens between infancy and age two. Both males and females are affected equally. Retinoblastoma can happen in either eye; however, in about 25% to 30% of the cases, the tumor is present in both eyes.
Signs and symptoms of retinoblastoma may include:
Leukocoria. A white light reflex that happens 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 for retinoblastoma may include one, or more, of the following:
Surgery (removal of the eyeball which may be followed up with an artificial eye implant)
Heat treatment (uses extreme heat directed toward cancer cells)
Laser therapy (uses light to destroy the blood vessels that nourish the tumor)
Cryotherapy (uses a freezing process to destroy the tumor)
Additional follow-up treatments may include one or more of the following:
Fitting and training for a prosthesis (artificial eye)
Blind or decreased vision adaptation training
Supportive care (for the side effects of treatment)
Antibiotics (to prevent or treat infection)