General Medical Information

Amblyopia

Jean Edwards Holt

Amblyopia is defined as unilateral defective vision, uncorrectable by glasses, in an otherwise normal eye. It occurs among about 5% of the young adult U.S. population and is commonly known as lazy eye. Half of all patients with amblyopia have or have had associated strabismus. Refractive amblyopia occurs if there is a marked difference in refractive errors of the two eyes. Like suppression to avoid diplopia in strabismus, the brain turns off the blurred image because of the greater refractive error to obtain a clearer object of regard. Occlusion amblyopia occurs if opacities of the ocular media, such as ptosis, cataract, or a macular lesions, prevent adequate sensory input. Retinoblastoma often manifests as esotropia due to macular involvement. All patients with strabismus need complete dilated ocular examinations.

Detection

Amblyopia, if detected early, often is curable. Treatment rarely is successful after 9 years of age, and best results are obtained if the patient is treated before the age of 5 years. The key to this disease is prevention. Prompt investigation is mandatory if a child has obvious strabismus. Even if the eyes appear straight during a routine pediatric examination, the examiner should observe how the child watches a light, how he or she follows a moving object, and how the child reacts to having each eye covered alternately. If amblyopia exists, the patient probably will resent, vocally or through evasive movement, covering of the “good” eye. Even before a child can give verbal response to visual acuity testing, he or she should be able to maintain central and steady fixation with each eye. By 3 years of age, visual acuity should be measured with picture cards or single E charts. The examiner must be certain that only one eye at a time is participating in the test. Children always peek if the fellow eye is not properly occluded. Young children may not quite reach 20/20, but as long as both eyes are near that standard and equal, the physician and parents need not be disturbed. Amblyopia may be present if there is a two-line difference between the two eyes on a visual acuity chart or if vision is only 20/30 to 20/40. Although amblyopia is a relatively minor visual impairment, many adults with a history of lazy eye have vision of only 20/200 or even less.

Treatment

Therapy for amblyopia is based on the simple idea of forcing the child to use the affected eye. Proper spectacle correction is followed by patching the normally used eye. The duration of treatment is monitored by the ophthalmologist. After maximal amblyopic treatment, surgical correction of any residual strabismus is undertaken to prevent recurrence of the amblyopia and to improve cosmesis and minimize psychosocial problems. Early detection and prompt referral of patients with strabismus or amblyopia can be one of the most important contributions of a physician treating pediatric patients.