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Newly identified factors that increase the risk of development of persistent esotropic amblyopia are delay in referral and anisometropia in children with infantile or accommodative esotropia.
"Amblyopia is associated with both infantile and accommodative esotropia," said Dr. Birch, director of the Pediatric Eye Research Laboratory, Retina Foundation of the Southwest, and adjunct professor of ophthalmology, University of Texas Southwestern Medical Center, Dallas.
In a group of 70 children with infantile esotropia, Dr. Birch recounted, amblyopia developed in about 75% at some time during the 5 years of follow-up; persistent amblyopia developed in about 12%. In another group of children with accommodative esotropia followed for more than 5 years, amblyopia developed in about 80%, and persistent amblyopia developed in about 20%.
With this in mind, Dr. Birch and colleagues enrolled 91 patients with infantile esotropia and 39 patients with accommodative esotropia in a study and subdivided the children into groups based on whether they had never developed amblyopia during follow-up, recovered from amblyopia with treatment, or had persistent amblyopia, defined as at least a 2-line difference in visual acuity between the eyes. Mean age of the children at the conclusion of follow-up was 9.5 years.
Potential risk factors that Dr. Birch and colleagues evaluated were age of onset of esotropia, delay in referral, age at surgery, initial refractive error, and initial anisometropia.
"We found that about 80% of children developed amblyopia at some point during the follow-up," Dr. Birch reported. Amblyopia developed in the children when they were aged a mean of about 13.6 months in the infantile esotropia group and about 36.8 months for those in the accommodative esotropia group. In both groups, about 50% recovered from amblyopia, persistent amblyopia developed in 20% to 30%, and amblyopia never developed in about 20% to 25%.
Early age of onset of esotropia may reflect more severe disease and a longer period of abnormal experience before the start of treatment, Dr. Birch said.
"This is the most difficult risk factor to assess," she added. This evaluation was undertaken with the aid of a questionnaire that helped parents differentiate between neonatal lack of coordination of eye movements and true esotropia and between constant and intermittent esotropia.
The investigators found the same age of onset regardless of which subgroup the patients were assigned to, that is, 2.5 months of age for the development of infantile esotropia and 25 months for the development of accommodative esotropia, according to Dr. Birch.
"Those with infantile esotropia who never developed amblyopia were referred within 2 months of onset; those with recovered amblyopia were referred within 3 months; and those with persistent amblyopia were referred longer than 4 months after onset," she reported. "Those children with accommodative esotropia and who never developed amblyopia were referred in less than 2 months after onset; those with recovered amblyopia were referred in less than 3.5 months; and those with persistent amblyopia were referred later than 5 months after onset."