Lazy Eye

Lazy eye

Definition

Lazy eye, or amblyopia, is an eye condition in which disuse causes reduced vision in an otherwise healthy eye. The affected eye is called the lazy eye. This vision defect occurs in 2–3% of American children. If not corrected before age eight, amblyopia will cause significant loss of stereoscopic vision, the ability to perceive three-dimensional depth.

Description

In some children, one eye functions better than the other. When a child begins to depend on the stronger eye, the weaker eye can become progressively weaker. Eventually, the weaker eye grows "lazy" from disuse. If left untreated beyond the early child-development years (from birth to seven years old), vision in the affected eye will be underdeveloped due to lack of use.

The impairment of vision in the lazy eye occurs in three phases. In the first (suspension) phase, the brain turns the weaker eye on and off. In the second (suppression) phase, the brain turns off the lazy eye indefinitely. At this point, the eye still has usable vision and can function well if the other eye is covered. In the last (amblyopia) phase, which occurs after age seven, the eye loses all the sensitivity that is essential for good vision because it has not been used for so long.

Lazy eye is a visual problem with potentially serious consequences. If left untreated, the affected child may have permanent loss of vision in the lazy eye. Because of loss of vision in one eye, these children cannot see three-dimensional images very well—all images appear flat. They also have problems with depth perception. This has serious consequences in their future ability to work in professions that require good vision in both eyes. Affected children also have increased risk of blindness should something happen to the good eye.

Causes & symptoms

The following are probable causes of lazy eye:

• Strabismus, or misalignment of a child's eyes (crossed eyes). This is the most frequent cause of lazy eye. Approximately half of all children with crossed eyes will develop a lazy eye. In children with crossed eyes, the images do not coordinate, thus confusing the brain. Therefore, the brain will suppress the image that comes from one eye and predominantly use the image from the stronger eye.
• Anisometropia (unequal refractive power). In this case, there is difference in image quality between the two eyes because one eye is severely nearsighted or farsighted. In other words, one eye focuses better than the other. The brain will mostly use the clearer image from the good eye. The other eye will become underdeveloped due to neglect.

• Congenital cataract. The lazy eye can not see well because its lens is already cloudy at birth.
• Ptosis (drooping eyelid). Vision in the lazy eye is blocked or impaired by the drooping eyelid.
• Corneal scarring. The image quality of the affected eye is poor due to scarring in the cornea.

The following are risk factors for amblyopia:

• rubella (German measles ) or other infections in the mother during pregnancy
• premature birth
• other family members with vision problems in childhood

Lazy eye may not present obvious symptoms. For this reason, it is important for small children to have regular eye examinations.

Diagnosis

Diagnosis of amblyopia is often made during visual screening during routine infant check-ups and in the preschool years (aged three to five). Premature babies need to have more frequent eye exams during early childhood to prevent this and other vision problems. A new photoscreening instrument that has been recently introduced appears to significantly increase the accuracy of diagnosis of these eye problems.

Treatment

The following alternative methods may complement conventional treatment of lazy eye. However, they are not replacements for conventional treatments. Because their effectiveness is not proven, parents should consult their child's ophthalmologist about the appropriate use of these methods (if any) in their child's overall eye treatment program.

Orthoptics (eye exercises)

Eye exercises can be helpful. Orthoptic exercises are designed to help the eyes move together and assist the fusing of the two images seen by the eyes. It can help correct faulty vision habit due to misalignment of the eyes and can teach the child to use both eyes effectively and comfortably. This form of therapy can be used before or after eye-realignment surgery to improve results.

Vision therapy

Vision training is a form of physical therapy for the brain and the eyes. It is a more extensive form of eye exercise and requires more frequent visits.

Acupuncture

One study shows that acupuncture treatment may be effective in treating anisometropia, a condition in which one eye focuses much better than the other. Acupuncture can reduce the differences in refractive powers between the eyes so that both eyes can have similar image quality. This helps reduce the amblyopia problem. However, its long-term effectiveness remains unknown.

Allopathic treatment

In order to treat lazy eye, the doctor has to identify and treat underlying causes. Depending on these underlying causes, the doctor may recommend surgical or nonsurgical treatments, as discussed below.

Refractive error correction

If both eyes need vision correction, children are given prescription glasses for better focus and to prevent misalignment of the eyes.

Forcing the use of the lazy eye

In many children with amblyopia, only one eye has a focusing problem or weak muscles. In order to force the affected eye to work, the doctor will cover the strong eye with a patch for most of the day for at least several weeks. Sometimes, this treatment requires as long as a year. The eye patch forces the lazy eye to work and thus, strengthens its vision and its muscles. This is the most common method used to treat lazy eye. To prevent the strong eye from becoming weaken due to disuse, the child is allowed to remove the patch so that he can see with the good eye for at least a few hours each day.

Another way to force the lazy eye to work harder is to use eye drops or ointment to blur the vision in the strong eye so that the child has to use the lazy eye to see. This method is not often used because it is associated with more adverse effects.

Surgical treatments

If the problem is caused by imbalances of the eye muscles and is not treatable with nonsurgical methods, the eye muscles can be realigned surgically to help the eyes coordinate better. Sometimes more than one surgery is required for the correction. Eye patch, glasses, or orthoptic exercises may be necessary following surgery to help the child use both eyes effectively. Long-term follow-up of surgical treatment indicates that it is highly effective in correcting the problem.

In patients whose amblyopia is caused by a congenital cataract in one eye, the cloudy lens is surgically removed and replaced by an intraocular lens. However, after surgery—even with eye glasses or contact lenses—this eye will still have poorer image quality than the good eye. Thus, the risk for amblyopia remains high. Therefore, nonsurgical treatment for lazy eye is often started after cataract surgery.

For a child whose vision is affected by a drooping eyelid, ptosis surgery is needed.

Expected results

With early diagnosis and treatment, children with amblyopia are expected to restore the sight in the lazy eye. However, if left untreated, the weak eye never develops adequate vision and the person may become functionally blind in that eye.

Prevention

Most cases of lazy eye are congenital, occurring since birth. However, if diagnosed early, vision loss in the affected eye can be prevented.

Resources

BOOKS

"Crossed Eyes." In Reader's Digest Guide to Medical Cures and Treatments. New York: Reader's Digest Association, 1996.

PERIODICALS

Broderick, Peter. "Pediatric Vision Screening for the Family Physician." American Family Physician 58, no. 3 (September 1, 1998): 691–700+. <http://www.aafp.org/afp/980901ap/broderic.html>.

Mills, Monte D. "The Eye in Childhood." American Family Physician 60, no. 3 (September 1, 1999): 907–18. <http://www.aafp.org/afp/990901ap/907.html>.

Paysse, Evelyn A., et al. "Detection of Red Reflex Asymmetry by Pediatric Residents Using the Bruckner Reflex Versus the MTI Photoscreener." Pediatrics 108 (October 2001): 997.

ORGANIZATIONS

American Academy of Ophthalmology. P.O. Box 7424, San Francisco, CA 94120-7424. (415) 561-8500. <http://www.eyenet.org>.

American Association For Pediatric Ophthalmology and Strabismus. c/o Denise De Losada Wilson. P.O. Box 193832, San Francisco, CA 94119-3832. (415) 561-8505. aapos@aao.org. <http://med-aapos.bu.edu>.

National Association for Parents of the Visually Impaired, Inc. P.O. Box 317, Watertown, MA 02471. (800) 562-6265. Fax: (617) 972-7444. <http://www.spedex.com/napvi>.

OTHER

"Congenital Eye Defects." The Merck Manual Online. [cited October 2002]. <http://www.merck.com/pubs/mmanual/section19/chapter261/261i.htm>.

Mai Tran

Rebecca J. Frey, PhD