EYE CONDITIONS

AMBLYOPIA

Amblyopia, also called “lazy eye,” is the most common cause of visual impairment in childhood. The condition affects approximately 2 to 3 out of every 100 children. Unless treated early, amblyopia usually persists into adulthood, and is the most common cause of monocular (one eye) visual impairment among children and young and middle-aged adults. Amblyopia will lead to permanent loss of sharp vision in one eye unless it is recognized and treated in the early preschool years.

Normal Vision

The brain and the eye work together to produce vision. Normal binocular vision depends on both eyes working together to fuse one clear image, and the brain blends the image from each eye into a single picture. Amblyopia is the medical term used when the vision in one of the eyes is reduced because the eye and the brain are not working together properly. The eye itself looks normal, but it is not being used normally because the brain is favoring the other eye.

• View a video demonstrating how amblyopia affects signals in the brain using Windows Media Player.
• View a video demonstrating how amblyopia affects signals in the brain using Quick Time Player.

Causes of Amblyopia

Amblyopia may be caused by any condition that affects normal visual development or use of the eyes. Amblyopia can be caused by strabismus or "crossed eye," an imbalance in the positioning of the two eyes. Strabismus can cause the eyes to cross in (esotropia) or turn out (exotropia). The child may see double because the brain is unable to blend the separate images. The child’s brain overcomes the double vision by ignoring the image seen by the turned eye. Since this eye is not used, normal vision does not develop.

Amblyopia can also occur in eyes that are straight, but have significant, unequal refractive errors. Sometimes amblyopia is caused when one eye is more nearsighted, farsighted, or astigmatic than the other eye. The affected eye does not receive proper visual stimulation; therefore, normal vision does not develop. Occasionally, amblyopia is caused by other eye conditions such as cataract which, due to light deprivation to the retina, interferes with proper vision development. Prolonged interference with the development of vision in either eye during a child’s early years may cause amblyopia. With lack of use and appropriate visual stimulation, the eye fails to develop the ability to see sharply. Most children adapt well to single eye vision. Parents may never suspect amblyopia, which is most often diagnosed during a thorough eye exam.

Treatment of Amblyopia

Treating amblyopia involves making the child use the amblyopic eye, or weaker eye, with the reduced vision. Currently, there are two ways used to do this:

Atropine
A drop of a drug called atropine is placed in the stronger eye once a day to temporarily blur the vision so that the child will prefer to use the eye with amblyopia. Treatment with atropine also stimulates vision in the weaker eye and helps the part of the brain that manages vision develop more completely. Surgery and/or glasses may be recommended to align strabismic eyes. Congenital cataracts should be surgically removed as soon as they are detected.

Patching
An opaque, adhesive patch is worn over the stronger eye for weeks to months. This therapy forces the child to use the eye with amblyopia. Patching stimulates vision in the weaker eye and helps the part of the brain that manages vision develop more completely. An infant’s vision may be improved in just a few weeks, but a four or five-year old usually must wear a patch for a number of months. Patching must be complete and uninterrupted for as long as the eye doctor orders. Parents must cooperate completely for treatment to be successful. The support of family and friends is also important to help the preschooler accept wearing the patch.

Previously, eye care professionals often thought that treating amblyopia in older children would be of little benefit. However, surprising results from a nationwide clinical trial show that many children ages 7 through 17 with amblyopia may benefit from treatments that are more commonly used on younger children. This study shows that age alone should not be used as a factor to decide whether or not to treat a child for amblyopia. Early detection and early treatment of amblyopia is imperative.

Preschool Vision Screening

Amblyopia is a serious vision handicap that can limit a child’s future in many ways educationally, recreationally and vocationally; however, it is usually correctable if found in the early preschool years. Every child between the ages of three and six should have a vision screening each year. If a child’s eyes have a suspicious appearance, or if there is a family history of amblyopia, a thorough eye exam is recommended in infancy.

Vision screening is offered annually in most area preschools by volunteers who are trained and supervised by Cleveland Sight Center’s Prevention of Blindness staff. If your child is not enrolled in a preschool, call (216) 791-8118, x277 and ask about preschool vision screening information. Email our Prevention of Blindness staff.